Qualia ( /ˈkwɑːliə/ or /ˈkweɪliə/), singular "quale" (Latin pronunciation: [ˈkwaːle]), from a Latin word meaning for "what sort" or "what kind," is a term used in philosophy to refer to subjective conscious experiences as 'raw feels'. Daniel Dennett writes that qualia is "an unfamiliar term for something that could not be more familiar to each of us: the ways things seem to us."^[1] Erwin Schrödinger had this counter-materialist take: "The sensation of colour cannot be accounted for by the physicist's objective picture of light-waves. Could the physiologist account for it, if he had fuller knowledge than he has of the processes in the retina and the nervous processes set up by them in the optical nerve bundles and in the brain? I do not think so."^[2]

Definitions[link]

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"Redness" is a commonly used example of a quale.

There are many definitions of qualia, which have changed over time. One of the simpler, broader definitions is "The 'what it is like' character of mental states. The way it feels to have mental states such as pain, seeing red, smelling a rose, etc."^[3]

Clarence Irving Lewis, in his book Mind and the World Order (1929), was the first to use the term "qualia" in its generally agreed modern sense.

There are recognizable qualitative characters of the given, which may be repeated in different experiences, and are thus a sort of universals; I call these "qualia." But although such qualia are universals, in the sense of being recognized from one to another experience, they must be distinguished from the properties of objects. Confusion of these two is characteristic of many historical conceptions, as well as of current essence-theories. The quale is directly intuited, given, and is not the subject of any possible error because it is purely subjective.

Frank Jackson (1982) later defined qualia as "...certain features of the bodily sensations especially, but also of certain perceptual experiences, which no amount of purely physical information includes" (p. 273).

Daniel Dennett identifies four properties that are commonly ascribed to qualia. According to these, qualia are:

1. ineffable; that is, they cannot be communicated, or apprehended by any other means than direct experience.
2. intrinsic; that is, they are non-relational properties, which do not change depending on the experience's relation to other things.
3. private; that is, all interpersonal comparisons of qualia are systematically impossible.
4. directly or immediately apprehensible in consciousness; that is, to experience a quale is to know one experiences a quale, and to know all there is to know about that quale.

If qualia of this sort exist, then a normally sighted person who sees red would be unable to describe the experience of this perception in such a way that a listener who has never experienced color will be able to know everything there is to know about that experience. Though it is possible to make an analogy, such as "red looks hot," or to provide a description of the conditions under which the experience occurs, such as "it's the color you see when light of 700-nm wavelength is directed at you," supporters of this kind of qualia contend that such a description is incapable of providing a complete description of the experience.

Another way of defining qualia is as "raw feels." A raw feel is a perception in and of itself, considered entirely in isolation from any effect it might have on behavior and behavioral disposition.^[4]

According to an argument put forth by Saul Kripke in his paper "Identity and Necessity" (1971), one key consequence of the claim that such things as raw feels can be meaningfully discussed—that qualia exist—is that it leads to the logical possibility of two entities exhibiting identical behavior in all ways despite one of them entirely lacking qualia. While very few ever claim that such an entity, called a philosophical zombie, actually exists, the mere possibility is claimed to be sufficient to refute physicalism.

Arguments for the existence of qualia[link]

Since it is by definition difficult or impossible to convey qualia verbally, it is difficult to demonstrate them directly in an argument; a more tangential approach is needed. Arguments for qualia generally come in the form of thought experiments designed to lead one to the conclusion that qualia exist.

The "What's it like to be?" argument[link]

Although it does not actually mention the word "qualia," Thomas Nagel's paper What Is it Like to Be a Bat?^[5] is often cited in debates over qualia. Nagel argues that consciousness has an essentially subjective character, a what-it-is-like aspect. He states that "an organism has conscious mental states if and only if there is something that it is like to be that organism — something it is like for the organism."^[5]:p.436 Nagel also suggests that the subjective aspect of the mind may not ever be sufficiently accounted for by the objective methods of reductionistic science. He claims that "[i]f we acknowledge that a physical theory of mind must account for the subjective character of experience, we must admit that no presently available conception gives us a clue how this could be done."^[5]:p.450 Furthermore, he states that "it seems unlikely that any physical theory of mind can be contemplated until more thought has been given to the general problem of subjective and objective."^[5]:p.450

The inverted spectrum argument[link]

Inverted qualia

The inverted spectrum thought experiment, originally developed by John Locke,^[6] invites us to imagine that we wake up one morning and find that for some unknown reason all the colors in the world have been inverted. Furthermore, we discover that no physical changes have occurred in our brains or bodies that would explain this phenomenon. Supporters of the existence of qualia argue that since we can imagine this happening without contradiction, it follows that we are imagining a change in a property that determines the way things look to us, but that has no physical basis.^[7][8] In more detail:

1. Metaphysical identity holds of necessity.
2. If something is possibly false, it is not necessary.
3. It is conceivable that qualia could have a different relationship to physical brain-states.
4. If it is conceivable, then it is possible.
5. Since it is possible for qualia to have a different relationship with physical brain-states, they cannot be identical to brain states (by 1).
6. Therefore, qualia are non-physical.

The argument thus claims that if we find the inverted spectrum plausible, we must admit that qualia exist (and are non-physical). Some philosophers find it absurd that an armchair argument can prove something to exist, and the detailed argument does involve a lot of assumptions about conceivability and possibility, which are open to criticism. Perhaps it is not possible for a given brain state to produce anything other than a given quale in our universe, and that is all that matters.

The idea that an inverted spectrum would be undetectable in practice is also open to criticism on more scientific grounds (see main article).^[7][8]

The zombie argument[link]

A similar argument holds that it is conceivable that there could be physical duplicates of people, called "zombies," without any qualia at all. These "zombies" would demonstrate outward behavior precisely similar to that of a normal human, but would not have a subjective phenomenology. It is worth noting that a necessary condition for the possibility of philosophical zombies is that there be no specific part or parts of the brain that directly give rise to qualia—the zombie can only exist if subjective consciousness is causally separate from the physical brain.

The explanatory gap argument[link]

Joseph Levine's paper Conceivability, Identity, and the Explanatory Gap takes up where the criticisms of conceivability arguments, such as the inverted spectrum argument and the zombie argument, leave off. Levine agrees that conceivability is flawed as a means of establishing metaphysical realities, but points out that even if we come to the metaphysical conclusion that qualia are physical, there is still an explanatory problem.

While I think this materialist response is right in the end, it does not suffice to put the mind-body problem to rest. Even if conceivability considerations do not establish that the mind is in fact distinct from the body, or that mental properties are metaphysically irreducible to physical properties, still they do demonstrate that we lack an explanation of the mental in terms of the physical.

However, such an epistemological or explanatory problem might indicate an underlying metaphysical issue—the non-physicality of qualia, even if not proven by conceivability arguments is far from ruled out.

In the end, we are right back where we started. The explanatory gap argument doesn't demonstrate a gap in nature, but a gap in our understanding of nature. Of course a plausible explanation for there being a gap in our understanding of nature is that there is a genuine gap in nature. But so long as we have countervailing reasons for doubting the latter, we have to look elsewhere for an explanation of the former.^[9]

The knowledge argument[link]

In an article "Epiphenomenal Qualia" (1982),^[10] Frank Jackson offers what he calls the "knowledge argument" for qualia. One example runs as follows:

Mary the colour scientist knows all the physical facts about colour, including every physical fact about the experience of colour in other people, from the behavior a particular colour is likely to elicit to the specific sequence of neurological firings that register that a colour has been seen. However, she has been confined from birth to a room that is black and white, and is only allowed to observe the outside world through a black and white monitor. When she is allowed to leave the room, it must be admitted that she learns something about the colour red the first time she sees it — specifically, she learns what it is like to see that colour.

This thought experiment has two purposes. First, it is intended to show that qualia exist. If we agree with the thought experiment, we believe that Mary gains something after she leaves the room—that she acquires knowledge of a particular thing that she did not possess before. That knowledge, Jackson argues, is knowledge of the quale that corresponds to the experience of seeing red, and it must thus be conceded that qualia are real properties, since there is a difference between a person who has access to a particular quale and one who does not.

The second purpose of this argument is to refute the physicalist account of the mind. Specifically, the knowledge argument is an attack on the physicalist claim about the completeness of physical truths. The challenge posed to physicalism by the knowledge argument runs as follows:

1. Before her release, Mary was in possession of all the physical information about color experiences of other people.
2. After her release, Mary learns something about the color experiences of other people.
   Therefore,
3. Before her release, Mary was not in possession of all the information about other people's color experiences, even though she was in possession of all the physical information.
   Therefore,
4. There are truths about other people's color experience that are not physical.
   Therefore,
5. Physicalism is false.

First Jackson argued that qualia are epiphenomenal: not causally efficacious with respect to the physical world. Jackson does not give a positive justification for this claim—rather, he seems to assert it simply because it defends qualia against the classic problem of dualism. Our natural assumption would be that qualia must be causally efficacious in the physical world, but some would ask how we could argue for their existence if they did not affect our brains. If qualia are to be non-physical properties (which they must be in order to constitute an argument against physicalism), some argue that it is almost impossible to imagine how they could have a causal effect on the physical world. By redefining qualia as epiphenomenal, Jackson attempts to protect them from the demand of playing a causal role.

Later, however, he rejected epiphenomenalism. This, he argues, is due to the fact that when Mary first sees red, she says "wow," so it must be Mary's qualia that causes her to say "wow." This contradicts epiphenomenalism. Since the Mary's room thought experiment seems to create this contradiction, there must be something wrong with it. This is often referred to as the "there must be a reply" reply.

The non-epistemic argument[link]

Those who hold to qualia being in a thoroughgoing sense "raw feels," that is, non-epistemic effects of a complex causal path emanating from the sense-organs (whether or not they respond to input from outside or inside the body) place them theoretically in a quite different account of the nature of consciousness.

The relation of qualia to the input is defined by those who propose this view in a way that is critical for the theory. They are emphatically not representations of entities, such as things and persons, existing out beyond the sense-organs. It is essential to the theory that no direct similarity (to confine the explanation to the visual field) is claimed between what appears within the field and any external entity or property that might be detected by the sense-organs, that is, for instance, no red in the brain matches a red light-ray or a red external object. There is, however, an indirect similarity, which Roy Wood Sellars was the first to delineate.^[11]

The key notion is that of what he called a "differential correlation" between the input and the state of the field, in that they were similar in the way they varied and in no other way. In order to grasp this notion, consider what the similarity is between the sound-track down the side of a strip of film and the sound heard in the cinema: clearly there is no direct similarity—one is a white strip varying in width, the other is a sound heard from loudspeakers—but they do co-vary, close variations in width corresponding to high frequencies, more open ones to low frequencies, and the widest sections matching the loudest sounds and the narrowest matching the softest. In the current debate this co-variation is being called "structural isomorphism" (there being a "same" [iso-] "shape" [-morph] in the structure).

The consequences are claimed to be significant. One objection thought to be powerful against the notion of qualia was that it forced us to see the visual field as an inner screen being looked at by a homunculus who himself would have a screen in his head, and so on ad infinitum in a vicious regress. This objection, characterized as the "Cartesian theater," is often employed by Daniel Dennett.^[12]

Yet it can be argued that the field in the brain bears no direct resemblance to what the eyes register, in that in the brain there are no eyes and no light-rays, though what occurs certainly varies with the light-rays' frequency and distribution, not perfectly, because all kinds of neural adjustments are made on the way to the final states. No homunculus is required, the reason being that the experience, not being itself a matter of light-rays, is a direct one. As Thomas Hobbes put it, we take notice of sense "by sense itself."^[13] So there is no visible "screen."

Any color experience the brain produces bears no direct likeness to the light-rays arriving at the retinas. This entails that there is no sensory color in the external world to be copied. One can draw a parallel with a snake that has sensory organs for picking up infrared rays: there is no sensory heat in the external world nor is there real heat in the snake's brain. They are similar in no more than their co-variation.

One further surprising outcome of this argument for qualia is that there cannot be a picture in the brain resembling an external scene, the unexpected reason being that actual pictures are not colored in the sensory manner; they merely reflect uncolored light-rays of different frequencies and intensities. This goes for paintings, photographs, television screens, etc., so they are ruled out as naïve analogies for the visual field. It is worth noting that television is not ruled out as a sophisticated analogy for the causal linkage between input and sensory registration as long as a structurally isomorphic link is held to (which entails that there is no copying of given "things" and "persons"), and the idea of a homunculus watching a screen is rejected.

The visual array is thus seen as an involuntary registration tied to an input of light-rays that bear evidence but not information about their sources. On this theory, qualia are thus no more than "natural signs" in H.P. Grice's sense, strictly comparable to seeing a dark cloud on the horizon as a sign of rain (Grice 1967). Philosophers who hold to this view see the knowledge argument as nugatory on both sides, since there is no given knowledge in qualia, whether of entities or of properties. One unusual entailment of this view is that we sense the real, but perceive only our stubbornly hypothetical, and hence experimental, "entities." As perceptions are always open to correction from others, as well as to surprising proofs of inadequacy from the real, there is no danger of solipsism. In particular, it may be one's own self that is corrected by others in a way that one has to concede. As hypothetical interpretations, entities-as-perceptions cannot be considered to be uncontroversial if viewed as direct causes of what is "objectified;" entities are only our own mutually adjustable guides to action. The Causal Theory of Perception, which takes objects-as-singular to exist, is thus regarded as mistaken, while a Causal Theory of Sensing is assumed within the theory.

If qualia thus present only evidence and not information, the question must then be put of how we come to assume that we perceive objects and familiar properties. Sellars, and more recently the psychologist Ernst von Glasersfeld, influenced by Jean Piaget, see perception as an affair of continual adaptation.^[14][15] According to them, it is our motivations that enforce unitary selections from the sensory evidence and simultaneously place them in memory tagged with fear or desire, this performed in the hope that purposive action will be guided successfully by them.

A demonstration: a child touches a hot radiator and the memory module immediately unifies elements from the qualia fields and places them in memory, marked with fear: perhaps at first it is only all ribbed appearances that become fearful "entities," but further experience will refine that judgement. In time the infant will come to experience "perturbations" of its initial perceiving which, in an evolutionary manner, will enforce adjustments. Finally the child approaches what von Glasersfeld calls a "viable" relationship with the evidence, in that action with regard to "the" percept produces results in most cases that satisfy motivation. At the entrance into language the child is enabled to receive suggestions for updating its understandings from others, including the formation of (now) his or her own selfhood, and, in dialogue, propose updatings for others so that they can adjust their motivational satisfactions. This is why von Glasersfeld is able to assert that all our perceptual recognitions are attended with "attentional pulses," that knowledge is always powered by motivation however much familiarity lulls us into the complacent view that we are seeing given entities, as is currently argued.^[16][17] This persuades us to see the word "mind" less in its form as a noun ("the mind") and more in its form as a verb ("Mind the step!"). Glasersfeld's use of the word "viable" for all our objectifications stresses the ineffaceable tentativeness of them all.

Another advantageous corollary is that, since perceptions are created by imagination, there is no difficulty in seeing how they can work apparently across time, as in "the specious present." In the middle of a well-known melody we can have an anticipatory perception of the rest of it without committing the theorist to the notion of sensing into the future. Together we behave with the projected logical "singularity" as if it is timelessly applicable, yet in every informative statement it is taken up only to be adjusted, to be taken up (so adjusted) again. One might make the analogy with the square root of negative one in a mathematical calculation, or with a catalyst in chemistry, in that we make use of it over and over again, only to abandon it each time.

Knowledge is thus theorized as a cooperative venture. Although we are all sensing differently (because no one's sense-organs perfectly match in range and sensitivity of response) and perceiving differently (because nor do our learning histories perfectly match), we all have to behave as if they did. If we did not, we could never get that minimal overlap of interpretations that allows a correction to go through. This is why a correction, especially of the self, can be such an uncanny surprise. No self is thus separate from the total venture of language, and, hence, it would seem that accusations of relativism and solipsism have no purchase on this theory. On the contrary it is claimed that it is the direct realists who are the relativists in being tempted to take the apparent immediacy of a purely "singular" entity as given in the way that they see "it;" they also veer towards solipsism in not seeing the inescapable intersubjectivity in all identifications, especially of the self.

One further advantage of the theory is that qualia, being strictly independent of the motivations of consciousness (recall the case of agnosics), are seen as not actually mental at all, but are part of the real, and thus, however strange they may be, are open to scientific inquiry.

Critics of qualia[link]

Daniel Dennett[link]

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In Consciousness Explained (1991) and "Quining Qualia" (1988),^[18] Daniel Dennett offers an argument against qualia that attempts to show that the above definition breaks down when one tries to make a practical application of it. In a series of thought experiments, which he calls "intuition pumps," he brings qualia into the world of neurosurgery, clinical psychology, and psychological experimentation. His argument attempts to show that, once the concept of qualia is so imported, it turns out that we can either make no use of it in the situation in question, or that the questions posed by the introduction of qualia are unanswerable precisely because of the special properties defined for qualia.

In Dennett's updated version of the inverted spectrum thought experiment, "alternative neurosurgery," you again awake to find that your qualia have been inverted—grass appears red, the sky appears orange, etc. According to the original account, you should be immediately aware that something has gone horribly wrong. Dennett argues, however, that it is impossible to know whether the diabolical neurosurgeons have indeed inverted your qualia (by tampering with your optic nerve, say), or have simply inverted your connection to memories of past qualia. Since both operations would produce the same result, you would have no means on your own to tell which operation has actually been conducted, and you are thus in the odd position of not knowing whether there has been a change in your "immediately apprehensible" qualia.

Dennett's argument revolves around the central objection that, for qualia to be taken seriously as a component of experience—for them to even make sense as a discrete concept—it must be possible to show that

a) it is possible to know that a change in qualia has occurred, as opposed to a change in something else; or that

b) there is a difference between having a change in qualia and not having one.

Dennett attempts to show that we cannot satisfy (a) either through introspection or through observation, and that qualia's very definition undermines its chances of satisfying (b).

Supporters of qualia could point out that in order for you to notice a change in qualia, you must compare your current qualia with your memories of past qualia. Arguably, such a comparison would involve immediate apprehension of your current qualia and your memories of past qualia, but not the past qualia itself. Furthermore, modern functional brain imaging has increasingly suggested that the memory of an experience is processed in similar ways and in similar zones of the brain as those originally involved in the original perception. This may mean that there would be asymmetry in outcomes between altering the mechanism of perception of qualia and altering their memories. If the diabolical neurosurgery altered the immediate perception of qualia, you might not even notice the inversion directly, since the brain zones which re-process the memories would themselves invert the qualia remembered. On the other hand, alteration of the qualia memories themselves would be processed without inversion, and thus you would perceive them as an inversion. Thus, you might know immediately if memory of your qualia had been altered, but might not know if immediate qualia were inverted or whether the diabolical neurosurgeons had done a sham procedure (Ungerleider, 1995).

Dennett also has a response to the "Mary the color scientist" thought experiment. He argues that Mary would not, in fact, learn something new if she stepped out of her black and white room to see the color red. Dennett asserts that if she already truly knew "everything about color," that knowledge would include a deep understanding of why and how human neurology causes us to sense the "quale" of color. Mary would therefore already know exactly what to expect of seeing red, before ever leaving the room. Dennett argues that the misleading aspect of the story is that Mary is supposed to not merely be knowledgeable about color but to actually know all the physical facts about it, which would be a knowledge so deep that it exceeds what can be imagined, and twists our intuitions.

If Mary really does know everything physical there is to know about the experience of color, then this effectively grants her almost omniscient powers of knowledge. Using this, she will be able to deduce her own reaction, and figure out exactly what the experience of seeing red will feel like.

Dennett finds that many people find it difficult to see this, so he uses the case of RoboMary to further illustrate what it would be like for Mary to possess such a vast knowledge of the physical workings of the human brain and color vision. RoboMary is an intelligent robot who, instead of the ordinary color camera-eyes, has a software lock such that she is only able to perceive black and white and shades in-between.

RoboMary can examine the computer brain of similar non-color-locked robots when they look at a red tomato, and see exactly how they react and what kinds of impulses occur. RoboMary can also construct a simulation of her own brain, unlock the simulation's color-lock and, with reference to the other robots, simulate exactly how this simulation of herself reacts to seeing a red tomato. RoboMary naturally has control over all of her internal states except for the color-lock. With the knowledge of her simulation's internal states upon seeing a red tomato, RoboMary can put her own internal states directly into the states they would be in upon seeing a red tomato. In this way, without ever seeing a red tomato through her cameras, she will know exactly what it is like to see a red tomato.

Dennett uses this example to show us that Mary's all-encompassing physical knowledge makes her own internal states as transparent as those of a robot or computer, and it is almost straightforward for her to figure out exactly how it feels to see red.

Perhaps Mary's failure to learn exactly what seeing red feels like is simply a failure of language, or a failure of our ability to describe experiences. An alien race with a different method of communication or description might be perfectly able to teach their version of Mary exactly how seeing the color red would feel. Perhaps it is simply a uniquely human failing to communicate first-person experiences from a third-person perspective. Dennett suggests that the description might even be possible using English. He uses a simpler version of the Mary thought experiment to show how this might work. What if Mary was in a room without triangles and was prevented from seeing or making any triangles? An English-language description of just a few words would be sufficient for her to imagine what it is like to see a triangle—she can simply and directly visualize a triangle in her mind. Similarly, Dennett proposes, it is perfectly, logically possible that the quale of what it is like to see red could eventually be described in an English-language description of millions or billions of words.

Paul Churchland[link]

According to Paul Churchland, Mary might be considered to be like a feral child. Feral children have suffered extreme isolation during childhood. Technically when Mary leaves the room, she would not have the ability to see or know what the color red is. A brain has to learn and develop how to see colors. Patterns need to form in the V4 section of the visual cortex. These patterns are formed from exposure to wavelengths of light. This exposure is needed during the early stages of brain development. In Mary's case, the identifications and categorizations of color will only be in respect to representations of black and white.^[19]

Such a response is disputable, however, on empirical grounds. Accounts such as those of Oliver Sacks in An Anthropologist on Mars concerning Virgil, who has his sight bestowed upon him in his forties, challenge the developmental view of color vision. It seems that whilst shapes must be visually learned through visual experience of shapes for the right concepts to be formed (i.e. the right neural connections to develop/be preserved), the same is not true of colors. There are connotations of primary-secondary quality distinctions here. Experiments are not decisive, but some views on experience require a non-developed ability—i.e. we need to be able to see something innately in order to get things off the ground—else we'd be trying to pull ourselves up by our bootstraps, as it were.

Gary Drescher[link]

In his book Good and Real (2006), Gary Drescher compares qualia with "gensyms" (generated symbols) in Common Lisp. These are objects that Lisp treats as having no properties or components and which can only be identified as equal or not equal to other objects. Drescher explains, "we have no introspective access to whatever internal properties make the red gensym recognizably distinct from the green [...] even though we know the sensation when we experience it."^{[20]:p.81–82} Under this interpretation of qualia, Drescher responds to the Mary thought experiment by noting that "knowing about red-related cognitive structures and the dispositions they engender — even if that knowledge were implausibly detailed and exhaustive — would not necessarily give someone who lacks prior color-experience the slightest clue whether the card now being shown is of the color called red." This does not, however, imply that our experience of red is non-mechanical; "on the contrary, gensyms are a routine feature of computer-programming languages."^[20]:p.82

David Lewis[link]

David Lewis has an argument that introduces a new hypothesis about types of knowledge and their transmission in qualia cases. Lewis agrees that Mary cannot learn what red looks like through her monochrome physicalist studies. But he proposes that this doesn't matter. Learning transmits information, but experiencing qualia doesn't transmit information; instead it communicates abilities. When Mary sees red, she doesn't get any new information. She gains new abilities—now she can remember what red looks like, imagine what other red things might look like and recognize further instances of redness. Lewis states that Jackson's thought experiment uses the "Phenomenal Information Hypothesis"—that is, the new knowledge that Mary gains upon seeing red is phenomenal information. Lewis then proposes a different "Ability Hypothesis" that differentiates between two types of knowledge: knowledge that (information) and knowledge how (abilities). Normally the two are entangled; ordinary learning is also an experience of the subject concerned, and people both learn information (for instance, that Freud was a psychologist) and gain ability (to recognize images of Freud). However in the thought experiment, Mary can only use ordinary learning to gain know-that knowledge. She is prevented from using experience to gain the know-how knowledge that would allow her to remember, imagine and recognize the color red.

We have the intuition that Mary has been deprived of some vital data to do with the experience of redness. It is also uncontroversial that some things cannot be learned inside the room; for example, we do not expect Mary to learn how to ski within the room. Lewis has articulated that information and ability are potentially different things. In this way, physicalism is still compatible with the conclusion that Mary gains new knowledge. It is also useful for considering other instances of qualia; "being a bat" is an ability, so it is know-how knowledge.^[21]

Marvin Minsky[link]

The veteran artificial intelligence researcher Marvin Minsky thinks the problems posed by qualia are essentially issues of complexity, or rather of mistaking complexity for simplicity.

Now, a philosophical dualist might then complain: "You've described how hurting affects your mind — but you still can't express how hurting feels." This, I maintain, is a huge mistake — that attempt to reify 'feeling' as an independent entity, with an essence that's indescribable. As I see it, feelings are not strange alien things. It is precisely those cognitive changes themselves that constitute what 'hurting' is — and this also includes all those clumsy attempts to represent and summarize those changes. The big mistake comes from looking for some single, simple, 'essence' of hurting, rather than recognizing that this is the word we use for complex rearrangement of our disposition of resources.^[22]

Michael Tye[link]

Michael Tye is perhaps the most outstanding example of those who hold to our directly confronting the objects of perception. In Tye's opinion, there are no qualia, no "veils of perception" between us and the referents of our thought. He describes our experience of an object in the world as "transparent." By this he means that no matter what private understandings and/or misunderstandings we may have of some public entity, it is still there before us in reality. The idea that qualia intervene between ourselves and their origins he regards as "a massive error"; as he says, "it is just not credible that visual experiences are systematically misleading in this way";^[17]:p.46 "the only objects of which you are aware are the external ones making up the scene before your eyes";^[17]:p.47 there are "no such things as the qualities of experiences" for "they are qualities of external surfaces (and volumes and films) if they are qualities of anything."^[17]:p.48 This insistence permits him to take our experience as having a reliable base since there is no fear of losing contact with the realness of public objects.

In Tye's thought there is no question of qualia without information being contained within them; it is always "an awareness that," always "representational." He characterizes the perception of children as a misperception of referents that are undoubtedly as present for them as they are for grown-ups. As he puts it, they may not know that "the house is dilapidated," but there is no doubt about their seeing the house. After-images are dismissed as presenting no problem for the Transparency Theory because, as he puts it, after-images being illusory, there is nothing that one sees.

Tye presents his theory about phenomena as having five basic elements, for which he has coined the acronym PANIC—Poised, Abstract, Nonconceptual, Intentional Content.^[17]:p.63 It is "Poised" in the sense that the phenomenal experience is always presented to the understanding, whether or not the agent is able to apply a concept to it. Tye adds that the experience is "maplike" in that, in most cases, it reaches through to the distribution of shapes, edges, volumes, etc. in the world—you may not be reading the "map" but, as with an actual map there is a reliable match with what it is mapping. It is "Abstract" because it is still an open question in a particular case whether you are in touch with a concrete object (someone may feel a pain in a "left leg" when that leg has actually been amputated). It is "Nonconceptual" because a phenomenon can exist although one does not have the concept by which to recognize it. Nevertheless, it is "Intentional" in the sense that it represents something, again whether or not the particular observer is taking advantage of that fact; this is why Tye calls his theory "representationalism." This last makes it plain that Tye believes that he has retained a direct contact with what produces the phenomena and is therefore not hampered by any trace of a "veil of perception." (See also.^[23])

Proponents of qualia[link]

David Chalmers[link]

David Chalmers formulated the hard problem of consciousness raising the issue of qualia to a new level of importance and acceptance in the field.^{[citation needed]} In his definitive paper "Absent Qualia, Fading Qualia, Dancing Qualia" he also argued for what he called "The principle of organizational invariance." In this paper he argues that if a system such as one of appropriately configured computer chips reproduces the functional organization of the brain, it will also reproduce the qualia associated with the brain.

E.J. Lowe[link]

Jonathan Lowe, of Durham University, denies that holding to indirect realism (in which we have access only to sensory features internal to the brain) necessarily implies a Cartesian dualism. He agrees with Bertrand Russell that our "retinal images," that is, the distributions across our retinas are connected to "patterns of neural activity in the cortex" (Lowe 1986). He defends a version of the Causal Theory of Perception in which a causal path can be traced between the external object and the perception of it. He is careful to deny that we do any inferring from the sensory field, a view which he believes allows us to found an access to knowledge on that causal connection. In a later work he moves closer to the non-epistemic theory in that he postulates "a wholly non-conceptual component of perceptual experience,"^[24] but he refrains from analyzing the relation between the perceptual and the "non-conceptual." Most recently he has drawn attention to the problems that hallucination raises for the direct realist and to their disinclination to enter the discussion on the topic.^[25]

J.B. Maund[link]

John Barry Maund, an Australian philosopher of perception at the University of Western Australia, is noteworthy in being the first^{[citation needed]} to draw attention to a key distinction which had been ignored in the current debate on qualia. Qualia are open to being described on two levels, a fact that he refers to as "dual coding." Using the Television Analogy (which, as we have seen in here, can be shorn of its objectionable aspects), he points out that, if asked what we see on a television screen there are two answers that we might give:

The states of the screen during a football match are unquestionably different from those of the screen during a chess game, but there is no way available to us of describing the ways in which they are different except by reference to the play, moves and pieces in each game.^[26]

He has refined the explanation by shifting to the example of a "Movitype" screen, often used for advertisements and announcements in public places. A Movitype screen consists of a matrix—or "raster" as the neuroscientists prefer to call it (from the Latin rastrum, a "rake"; think of the lines on a TV screen as "raked" across)—that is made up of an array of tiny light-sources. A computer-led input can excite these lights so as to give the impression of letters passing from right to left, or even, on the more advanced forms now commonly used in advertisements, to show moving pictures. Maund's point is as follows. It is obvious that there are two ways of describing what you are seeing. We could either adopt the everyday public language and say "I saw some sentences, followed by a picture of a 7-Up can." Although that is a perfectly adequate way of describing the sight, nevertheless, there is a scientific way of describing it which bears no relation whatsoever to this commonsense description. One could ask the electronics engineer to provide us with a computer print-out staged across the seconds that you were watching it of the point-states of the raster of lights. This would no doubt be a long and complex document, with the state of each tiny light-source given its place in the sequence. The interesting aspect of this list is that, although it would give a comprehensive and point-by-point-detailed description of the state of the screen, nowhere in that list would there be a mention of "English sentences" or "a 7-Up can."

What this makes clear is that there are two ways to describe such a screen, (1) the "commonsense" one, in which publicly recognizable objects are mentioned, and (2) an accurate point-by-point account of the actual state of the field, but makes no mention of what any passer-by would or would not make of it. This second description would be non-epistemic from the common sense point of view, since no objects are mentioned in the print-out, but perfectly acceptable from the engineer's point of view. Note that, if one carries this analysis across to human sensing and perceiving, this rules out Daniel Dennett's claim that all qualiaphiles must regard qualia as "ineffable," for at this second level they are in principle quite "effable"—indeed, it is not ruled out that some neurophysiologist of the future might be able to describe the neural detail of qualia at this level.

Maund has also extended his argument particularly with reference of color.^[27] Color he sees as a dispositional property, not an objective one, an approach which allows for the facts of difference between person and person, and also leaves aside the claim that external objects are colored. Colors are therefore "virtual properties," in that it is as if things possessed them; although the naïve view attributes them to objects, they are intrinsic, non-relational inner experiences.

Moreland Perkins[link]

In his book Sensing the World,^[28] Moreland Perkins argues that qualia need not be identified with their objective sources: a smell, for instance, bears no direct resemblance to the molecular shape that gives rise to it, nor is a toothache actually in the tooth. He is also like Hobbes in being able to view the process of sensing as being something complete in itself; as he puts it, it is not like "kicking a football" where an external object is required—it is more like "kicking a kick," an explanation which entirely avoids the familiar Homunculus Objection, as adhered to, for example, by Gilbert Ryle. Ryle was quite unable even to entertain this possibility, protesting that "in effect it explained the having of sensations as the not having of sensations."^[29] However, A.J. Ayer in a rejoinder correctly identified this objection as "very weak" as it betrayed an inability to detach the notion of eyes, indeed any sensory organ, from the neural sensory experience.^[30]

Ramachandran and Hirstein[link]

V.S. Ramachandran and William Hirstein^[31] proposed three laws of qualia (with a fourth later added), which are "functional criteria that need to be fulfilled in order for certain neural events to be associated with qualia" by philosophers of the mind:

1. Qualia are irrevocable and indubitable. You don't say 'maybe it is red but I can visualize it as green if I want to'. An explicit neural representation of red is created that invariably and automatically 'reports' this to higher brain centres.
2. Once the representation is created, what can be done with it is open-ended. You have the luxury of choice, e.g., if you have the percept of an apple you can use it to tempt Adam, to keep the doctor away, bake a pie, or just to eat. Even though the representation at the input level is immutable and automatic, the output is potentially infinite. This isn't true for, say, a spinal reflex arc where the output is also inevitable and automatic. Indeed, a paraplegic can even have an erection and ejaculate without an orgasm.
3. Short-term memory. The input invariably creates a representation that persists in short-term memory — long enough to allow time for choice of output. Without this component, again, you get just a reflex arc.
4. Attention. Qualia and attention are closely linked. You need attention to fulfil criterion number two; to choose. A study of circuits involved in attention, therefore, will shed much light on the riddle of qualia.^[32]

They proposed that the phenomenal nature of qualia could be communicated (as in "oh that is what salt tastes like") if brains could be appropriately connected with a "cable of neurons."^[31] If this turned out to be possible this would scientifically prove or objectively demonstrate the existence and the nature of qualia.

Antti Revonsuo[link]

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Antti Revonsuo is a Finnish neuroscientist who wishes to transform the whole approach to qualia—and by implication, consciousness itself—by treating the problems from a "biological realist" perspective.^[33] He is prepared to accept the notion of the phenomenal-as-real, together with aspects of it that the direct realists are still rejecting, namely, that the organism with sensory access to its world (and that includes its own body) is equipped by evolution with a "virtual space" in which sensory presentations in the brain enact a "world-simulation." The phenomenal space is distinct from physical space, an idea that many find difficult to comprehend. Like John Smythies (see the next entry), he is not at all daunted by the strangeness of the high speculation that is necessitated at such an early stage of scientific inquiry.

The biological emphasis naturally places motivation as the key to the nature of mind, and it will be no surprise that he embraces the non-epistemic argument. For example, he notes that as soon as attention (the focus of current motivation, that is, of fear or desire) is withdrawn from the current selection from the sensory field, that portion, hitherto conceptualized as of immediate relevance, "dissolves back into a bundle of features" which we ignore precisely because we have lost interest in them. He characterizes the non-epistemic field thus: "qualities as such, without any organization, are barely worth having," the reason being that, away from attention, they revert to their knowledge-less, information-less state, devoid of interest, of relevance to purpose. The old objections (such as the Homunculus Objection) he summarily disposes of: phenomena he describes as "self-presenting"—it is naïve to carry over from our mundane assumptions about vision the idea that in the brain a separate "subject" must be distinct from something objective it sees at a distance.

Howard Robinson and William Robinson[link]

Howard Robinson is a philosopher who has concentrated his research within the philosophy of mind. Taking what has been through the latter part of the last century an unfashionable stance, he has consistently argued against those explanations of sensory experience that would reduce them to physical origins. He has never regarded the theory of sense-data as refuted, but has set out to refute in turn the objections which so many have considered to be conclusive. The version of the theory of sense-data he defends takes what is before consciousness in perception to be qualia as mental presentations that are causally linked to external entities, but which are not physical in themselves. Unlike the philosophers so far mentioned, he is therefore a dualist, one who takes both matter and mind to have real and metaphysically distinct natures. His books (particularly Matter and Sense and Perception^[34]) are characterized by the thoroughness with which he deals with the arguments of opposing philosophers, thus setting a professional example that it would be well for his opponents to follow (for there has been a tendency to take for granted that the theory of sense-data is wholly obsolescent). In one of his most recent articles he takes the physicalist to task for ignoring the fact that sensory experience can be entirely free of representational character. He cites phosphenes as a stubborn example (phosphenes are flashes of neural light that result either from sudden pressure in the brain—as induced, for example, by intense coughing, or through direct physical pressure on the retina), and points out that it is grossly counter-intuitive to argue that these are not visual experiences on a par with open-eye seeing.

William Robinson (no relation) takes a very similar view to that of his namesake. In his most recent book, Understanding Phenomenal Consciousness,^[35] he is unusual as a dualist in calling for research programs that investigate the relation of qualia to the brain. The problem is so stubborn, he says, that too many philosophers would prefer "to explain it away," but he would rather have it explained and does not see why the effort should not be made. However, he does not expect there to be a straightforward scientific reduction of phenomenal experience to neural architecture; on the contrary he regards this as a forlorn hope. The "Qualitative Event Realism" that Robinson espouses sees phenomenal consciousness as caused by brain events but not identical with them, being non-material events.

It is noteworthy that he refuses to set aside the vividness—and commonness—of mental images, both visual and aural, standing here in direct opposition to Daniel Dennett, who has difficulty in crediting the experience in others. He is similar to Moreland Perkins in keeping his investigation wide enough to apply to all the senses.

Edmond Wright[link]

Edmond Wright is a philosopher who considers the intersubjective aspect of perception.^[36][37] From Locke onwards it had been normal to frame perception problems in terms of a single subject S looking at a single entity E with a property p. However, if we begin with the facts of the differences in sensory registration from person to person, coupled with the differences in the criteria we have learned for distinguishing what we together call "the same" things, then a problem arises of how two persons align their differences on these two levels so that they can still get a practical overlap on parts of the real about them—and, in particular, update each other about them.

Wright mentions being struck with the hearing difference between himself and his son, discovering that his son could hear sounds up to nearly 20 kilohertz while his range only reached to 14 kHz or so. This implies that a difference in qualia could emerge in human action (for example, the son could warn the father of a high-pitched escape of a dangerous gas kept under pressure, the sound-waves of which would be producing no qualia evidence at all for the latter). The relevance for language thus becomes critical, for an informative statement can best be understood as an updating of a perception—and this may involve a radical re-selection from the qualia fields viewed as non-epistemic, even perhaps of the presumed singularity of "the" referent, a fortiori if that "referent" is the self. Here he distinguishes his view from that of Revonsuo, who too readily makes his "virtual space" "egocentric."

Wright's particular emphasis has been on what he asserts is a core feature of communication, that, in order for an updating to be set up and made possible, both speaker and hearer have to behave as if they have identified "the same singular thing," which, he notes, partakes of the structure of a joke or a story.^[36] Wright says that this systematic ambiguity seems to opponents of qualia to be a sign of fallacy in the argument (as ambiguity is in pure logic) whereas, on the contrary, it is sign—in talk about "what" is perceived—of something those speaking to each other have to learn to take advantage of. In extending this analysis, he has been led to argue for an important feature of human communication being the degree and character of the faith maintained by the participants in the dialogue, a faith that has priority over what has before been taken to be the key virtues of language, such as "sincerity," "truth" and "objectivity". Indeed, he considers that to prioritize them over faith is to move into superstition.

Erwin Schrödinger[link]

Erwin Schrödinger, a theoretical physicist and one of the leading pioneers of quantum mechanics, also published in the areas of colorimetry and color perception. In several of his philosophical writings, he defends the notion that qualia are not physical.

The sensation of colour cannot be accounted for by the physicist's objective picture of light-waves. Could the physiologist account for it, if he had fuller knowledge than he has of the processes in the retina and the nervous processes set up by them in the optical nerve bundles and in the brain? I do not think so.^[2]

He continues on to remark that subjective experiences do not form a one-to-one correspondence with stimuli. For example, light of wavelength in the neighborhood of 590 nm produces the sensation of yellow, whereas exactly the same sensation is produced by mixing red light, with wavelength 760 nm, with green light, at 535 nm. From this he concludes that there is no "numerical connection with these physical, objective characteristics of the waves" and the sensations they produce.

Neurological blending of perspectives[link]

When looked at philosophically, qualia become a tipping point between the physical and the mental, which polarizes the discussion, as we've seen above, into "Do they or do they not exist?" and "Are they physical or beyond the physical?" However, from a strictly neurological perspective, they can both exist, and be very important to the organism's survival, and be the result of strict neuronal oscillation, and still not rule out the metaphysical. A good example of this pro/con blending is in Rodolfo Llinás's I of the Vortex (MIT Press, 2002, pp. 202–207). Llinás argues that qualia are ancient and necessary for an organism's survival and a product of neuronal oscillation. Llinás gives the evidence of anesthesia of the brain and subsequent stimulation of limbs to demonstrate that qualia can be "turned off" with changing only the variable of neuronal oscillation (local brain electrical activity), while all other connections remain intact, arguing strongly for an oscillatory—electrical origin of qualia, or important aspects of them. Others^[who?] criticize this position by arguing that qualia are not necessary at all for organisms' survival, since they can do it perfectly without it.

Other issues[link]

Indeterminacy[link]

It is possible to apply a criticism similar to Nietzsche's criticism of Kant's "thing in itself" to qualia: Qualia are unobservable in others and unquantifiable in us. We cannot possibly be sure, when discussing individual qualia, that we are even discussing the same phenomena. Thus, any discussion of them is of indeterminate value, as descriptions of qualia are necessarily of indeterminate accuracy.^{[citation needed]}. Qualia can be compared to "things in themselves" in that they have no publicly demonstrable properties; this, along with the impossibility of being sure that we are communicating about the same qualia, makes them of indeterminate value and definition in any philosophy in which proof relies upon precise definition.^{[citation needed]}. On the other hand, qualia could be considered akin to Kantian phenomena since they are held to be seemings of appearances. Revonsuo, however, considers that, within neurophysiological inquiry, a definition at the level of the fields may become possible (just as we can define a television picture at the level of liquid crystal pixels).

Causal efficacy[link]

The position known as epiphenomenalism, which states that consciousness lies outside the physical world, and does not have any causal power over it, is often regarded as unlikely,^[38] if only because our own consciousness seem to be causally active. In order to avoid epiphenomenalism, one who believes that qualia are nonphysical would need to embrace something like interactionist dualism; or perhaps emergentism, the claim that there are as yet unknown causal relations between the mental and physical. This in turn would imply that qualia can be detected by an external agency through their causal powers.

Epistemological issues[link]

To illustrate: one might be tempted to give as examples of qualia "the pain of a headache, the taste of wine, or the redness of an evening sky." But this list of examples already prejudges a central issue in the current debate on qualia.^{[citation needed]} An analogy might make this clearer. Suppose someone wants to know the nature of the liquid crystal pixels on a television screen, those tiny elements that provide all the distributions of color that go to make up the picture. It would not suffice as an answer to say that they are the "redness of an evening sky" as it appears on the screen. We would protest that their real character was being ignored. One can see that relying on the list above assumes that we must tie sensations not only to the notion of given objects in the world (the "head," "wine," "an evening sky"), but also to the properties with which we characterize the experiences themselves ("redness," for example).

Nor is it satisfactory to print a little red square as at the top of the article, for, since each person has a slightly different registration of the light-rays,^[39] it confusingly suggests that we all have the same response. Imagine in a television shop seeing "a red square" on twenty screens at once, each slightly different—something of vital importance would be overlooked if a single example were to be taken as defining them all.

Yet it has been argued whether or not identification with the external object should still be the core of a correct approach to sensation, for there are many who state the definition thus because they regard the link with external reality as crucial. If sensations are defined as "raw feels," there arises a palpable threat to the reliability of knowledge. The reason has been given that, if one sees them as neurophysiological happenings in the brain, it is difficult to understand how they could have any connection to entities, whether in the body or the external world. It has been declared, by John McDowell for example, that to countenance qualia as a "bare presence" prevents us ever gaining a certain ground for our knowledge.^[40] The issue is thus fundamentally an epistemological one: it would appear that access to knowledge is blocked if one allows the existence of qualia as fields in which only virtual constructs are before the mind.

His reason is that it puts the entities about which we require knowledge behind a "veil of perception," an occult field of "appearance" which leaves us ignorant of the reality presumed to be beyond it. He is convinced that such uncertainty propels into the dangerous regions of relativism and solipsism: relativism sees all truth as determined by the single observer; solipsism, in which the single observer is the only creator of and legislator for his or her own universe, carries the assumption that no one else exists. These accusations constitute a powerful ethical argument against qualia being something going on in the brain, and these implications are probably largely responsible for the fact that in the 20th century it was regarded as not only freakish, but also dangerously misguided to uphold the notion of sensations as going on inside the head. The argument was usually strengthened with mockery at the very idea of "redness" being in the brain: the question was—and still is^[41]—"How can there be red neurons in the brain?" which strikes one as a justifiable appeal to common sense.

To maintain a philosophical balance, the argument for "raw feels" needs to be set side by side with the claim above. Viewing sensations as "raw feels" implies that initially they have not yet—to carry on the metaphor—been "cooked," that is, unified into "things" and "persons," which is something the mind does after the sensation has responded to the blank input, that response driven by motivation, that is, initially by pain and pleasure, and subsequently, when memories have been implanted, by desire and fear. Such a "raw-feel" state has been more formally identified as "non-epistemic." In support of this view, the theorists cite a range of empirical facts. The following can be taken as representative. There are brain-damaged persons, known as "agnosics" (literally "not-knowing") who still have vivid visual sensations but are quite unable to identify any entity before them, including parts of their own body. There is also the similar predicament of persons, formerly blind, who are given sight for the first time—and consider what it is a newborn baby must experience. A German psychologist of the 19th century, Hermann von Helmholtz, proposed a simple experiment to demonstrate the non-epistemic nature of qualia: his instructions were to stand in front of a familiar landscape, turn your back on it, bend down and look at the landscape between your legs—you will find it difficult in the upside-down view to recognize what you found familiar before.^[42] These examples suggest that a "bare presence," that is, knowledgeless sensation that is no more than evidence, may really occur. Present supporters of the non-epistemic theory thus regard sensations as only data in the sense that they are "given" (Latin datum, "given") and fundamentally involuntary, which is a good reason for not regarding them as basically mental. In the last century they were called "sense-data" by the proponents of qualia, but this led to the confusion that they carried with them reliable proofs of objective causal origins. For instance, one supporter of qualia was happy to speak of the redness and bulginess of a cricket ball as a typical "sense-datum,"^[43] though not all of them were happy to define qualia by their relation to external entities (see Roy Wood Sellars^[44]). The modern argument, following Sellars' lead, centers on how we learn under the regime of motivation to interpret the sensory evidence in terms of "things," "persons" and "selves" through a continuing process of feedback.

The definition of qualia thus is governed by one's point of view, and that inevitably brings with it philosophical and neurophysiological presuppositions. The question, therefore, of what qualia can be raises profound issues in the philosophy of mind, since some materialists want to deny their existence altogether: on the other hand, if they are accepted, they cannot be easily accounted for as they raise the difficult problem of consciousness. There are committed dualists such as Richard L. Amoroso who believe that the mental and the material are two distinct aspects of reality.^[45] In contrast, there are tough-minded direct realists for whom the thought of qualia is unscientific as there appears to be no way of making them fit within the modern scientific picture; and there are committed proselytizers for a final truth who reject them as forcing knowledge out of reach.

See also[link]

Wikibooks has a book on the topic of Consciousness Studies

Philosophy portal

Notes[link]

References[link]

Look up qualia in Wiktionary, the free dictionary.

• Online papers on qualia, by various authors, compiled by David Chalmers
• Absent Qualia, Dancing Qualia, Fading Qualia, by David Chalmers
• "Field Guide to the Philosophy of Mind"
  • The Knowledge Argument, by Torin Alter
  • Qualia Realism., by William Robinson.
• Qualia! (Now Showing at a Theatre Near You), by Eric Lormand. A response to Dennett.
• Quining Qualia, by Daniel Dennett
• The Stanford Encyclopedia of Philosophy:
  • Inverted Qualia, by Alex Byrne.
  • Qualia, by Michael Tye.
  • Qualia: The Knowledge Argument, by Martine Nida-Rümelin.
• Three Laws of Qualia, by Ramachandran and Hirstein (biological perspective).
• Brainy Mind (qualia and the sensation of time) by Richard Gregory

Hilary Whitehall Putnam

Born	(1926-07-31) July 31, 1926 (age 85) Chicago, Illinois, U.S.
Era	20th-century philosophy
Region	Western Philosophy
School	Analytic Pragmatism
Main interests	Philosophy of mind Philosophy of language Philosophy of mathematics Metaphilosophy Epistemology
Notable ideas	Multiple realizability Functionalism Causal theory of reference Semantic externalism Brain in a vat · Twin Earth Internal realism
Influenced by W.V.O. Quine, John Dewey, Hans Reichenbach, Alan Turing, Immanuel Kant, Nelson Goodman, Charles Sanders Peirce, William James, Ludwig Wittgenstein, Søren Kierkegaard, Karl Marx, Sigmund Freud[1]
Influenced Jerry Fodor, Ned Block, Joseph LeDoux, Tyler Burge, David Marr, Daniel Dennett, David Lewis, Donald Davidson

Hilary Whitehall Putnam (born July 31, 1926) is an American philosopher, mathematician and computer scientist, who has been a central figure in analytic philosophy since the 1960s, especially in philosophy of mind, philosophy of language, philosophy of mathematics, and philosophy of science.^[2] He is known for his willingness to apply an equal degree of scrutiny to his own philosophical positions as to those of others, subjecting each position to rigorous analysis until he exposes its flaws.^[3] As a result, he has acquired a reputation for frequently changing his own position.^[4] Putnam is currently Cogan University Professor Emeritus at Harvard University.

In philosophy of mind, Putnam is known for his argument against the type-identity of mental and physical states based on his hypothesis of the multiple realizability of the mental, and for the concept of functionalism, an influential theory regarding the mind-body problem.^[2][5] In philosophy of language, along with Saul Kripke and others, he developed the causal theory of reference, and formulated an original theory of meaning, inventing the notion of semantic externalism based on a famous thought experiment called Twin Earth.^[6]

In philosophy of mathematics, he and his mentor W. V. Quine developed the "Quine-Putnam indispensability thesis," an argument for the reality of mathematical entities,^[7] later espousing the view that mathematics is not purely logical, but "quasi-empirical".^[8] In the field of epistemology, he is known for his critique of the well known "brain in a vat" thought experiment. This thought experiment appears to provide a powerful argument for epistemological skepticism, but Putnam challenges its coherence.^[9] In metaphysics, he originally espoused a position called metaphysical realism, but eventually became one of its most outspoken critics, first adopting a view he called "internal realism",^[10] which he later abandoned in favor of a pragmatist-inspired direct realism. Putnam's "direct realism" aims to return the study of metaphysics to the way people actually experience the world, rejecting the idea of mental representations, sense data, and other intermediaries between mind and world.^[11] In his later work, Putnam has become increasingly interested in American pragmatism, Jewish philosophy, and ethics, thus engaging with a wider array of philosophical traditions. He has also displayed an interest in metaphilosophy, seeking to "renew philosophy" from what he identifies as narrow and inflated concerns.

Outside philosophy, Putnam has contributed to mathematics and computer science. Together with Martin Davis he developed the Davis–Putnam algorithm for the Boolean satisfiability problem^[12] and he helped demonstrate the unsolvability of Hilbert's tenth problem.^[13] He has been at times a politically controversial figure, especially for his involvement with the Progressive Labor Party in the late 1960s and early 1970s.^[14][15]

Personal life[link]

Putnam was born in Chicago, Illinois in 1926. His father, Samuel Putnam, was a scholar of Romance languages, columnist and translator who wrote for the Daily Worker, a publication of the American Communist Party from 1936 to 1946 (when he became disillusioned with communism).^[16] As a result of his father's commitment to communism, Putnam had a secular upbringing, although his mother, Riva, was Jewish.^[3] The family lived in France until 1934, when they returned to the United States, settling in Philadelphia.^[3] Putnam attended Central High School; there he met Noam Chomsky, who was a year behind him. The two have been friends—and often intellectual opponents—ever since.^[17] Putnam studied mathematics and philosophy at the University of Pennsylvania, receiving his BA (undergraduate degree) and becoming a member of the Philomathean Society, one of the oldest collegiate literary societies in the U.S.^[3][14] He went on to do graduate work in philosophy at Harvard University,^[3] and later at UCLA's Philosophy Department, where he received his Ph.D. in 1951 for a dissertation entitled "The Meaning of the Concept of Probability in Application to Finite Sequences". Putnam's teacher Hans Reichenbach (his dissertation supervisor) was a leading figure in logical positivism, the dominant school of philosophy of the day; one of Putnam's most consistent positions has been his rejection of logical positivism as self-defeating.^[14]

After briefly teaching at Northwestern, Princeton, and MIT, he moved to Harvard in 1965 with his wife, Ruth Anna Jacobs, who took a teaching position in philosophy at Wellesley College.^[14] Hilary and Ruth Anna were married in 1962.^[18] Ruth Anna Jacobs, descendant of a family with a long scholarly tradition in Gotha (her ancestor was the German classical scholar Christian Friedrich Wilhelm Jacobs), was born in Berlin, Germany,^[19] in 1927 to anti-Nazi political-activist parents and, like Putnam himself, she was raised an atheist (her mother was Jewish and her father had been from a Christian background).^[18] The Putnams, rebelling against the anti-Semitism that they had experienced during their youth, decided to establish a traditional Jewish home for their children.^[18] Since they had no experience with the rituals of Judaism, they sought out invitations to other Jews' homes for Seder. They had "no idea how to do it [themselves]", in the words of Ruth Anna. They therefore began to study Jewish ritual and Hebrew, and became more Jewishly interested, identified, and active. In 1994, Hilary Putnam celebrated a belated Bar Mitzvah service. His wife had a Bat Mitzvah service four years later.^[18]

Hilary was a popular teacher at Harvard. In keeping with the family tradition, he was politically active.^[14] In the 1960s and early 1970s, he was an active supporter of civil rights causes and an opponent of American military intervention in Vietnam.^[15] In 1963, he organized one of the first faculty and student committees at MIT against the war. Putnam was disturbed when he learned from reading the reports of David Halberstam that the U.S. was "defending" South Vietnamese peasants from the Vietcong by poisoning their rice crops.^[14] After moving to Harvard in 1965, he organized campus protests and began teaching courses on Marxism. Hilary became an official faculty advisor to the Students for a Democratic Society and, in 1968, became a member of the Progressive Labor Party (PLP).^[14]

He was elected a Fellow of the American Academy of Arts and Sciences in 1965.^[20] After 1968, his political activities were centered on the PLP.^[15] The Harvard administration considered these activities disruptive and attempted to censure Putnam, but two other faculty members criticized the procedures.^[21] Putnam permanently severed his ties with the PLP in 1972.^[22] In 1997, at a meeting of former draft resistance activists at Arlington Street Church in Boston, Putnam described his involvement with the PLP as a mistake. He said that he had been impressed at first with PLP's commitment to alliance-building, and its willingness to attempt to organize from within the armed forces.^[15]

In 1976, he was elected President of the American Philosophical Association. The following year, he was selected as Walter Beverly Pearson Professor of Mathematical Logic, in recognition of his contributions to philosophy of logic and mathematics.^[14] While breaking with his radical past, Putnam has never abandoned his belief that academics have a particular social and ethical responsibility toward society. He has continued to be forthright and progressive in his political views, as expressed in the articles "How Not to Solve Ethical Problems" (1983) and "Education for Democracy" (1993).^[14]

Putnam is a Corresponding Fellow of the British Academy. He retired from teaching in June 2000, but, as of 2009, he still gives a seminar almost yearly at Tel Aviv University. He is the Cogan University Professor Emeritus at Harvard University. He is also a founding patron of the small liberal arts college Ralston College. His corpus includes five volumes of collected works, seven books, and more than 200 articles. Putnam's renewed interest in Judaism has inspired him to publish several recent books and essays on the topic.^[23] With his wife, he has co-authored several books and essays on the late-19th century American pragmatist movement.^[14]

Philosophy of mind[link]

Multiple realizability[link]

An illustration of multiple realizability. M stands for mental and P stands for physical. It can be seen that more than one P can instantiate one M, but not vice versa. Causal relations between states are represented by the arrows (M1 goes to M2, etc.)

Putnam's best-known work concerns philosophy of mind. His most noted original contributions to that field came in several key papers published in the late 1960s that set out the hypothesis of multiple realizability.^[24] In these papers, Putnam argues that, contrary to the famous claim of the type-identity theory, it is not necessarily true that "Pain is identical to C-fibre firing." Pain, according to Putnam's papers, may correspond to utterly different physical states of the nervous system in different organisms, and yet they all experience the same mental state of "being in pain".

Putnam cited examples from the animal kingdom to illustrate his thesis. He asked whether it was likely that the brain structures of diverse types of animals realize pain, or other mental states, the same way. If they do not share the same brain structures, they cannot share the same mental states and properties. The answer to this puzzle had to be that mental states were realized by different physical states in different species. Putnam then took his argument a step further, asking about such things as the nervous systems of alien beings, artificially intelligent robots and other silicon-based life forms. These hypothetical entities, he contended, should not be considered incapable of experiencing pain just because they lack the same neurochemistry as humans. Putnam concluded that type-identity theorists had been making an "ambitious" and "highly implausible" conjecture which could be disproven with one example of multiple realizability.^[25] This argument is sometimes referred to as the "likelihood argument".^[24]

Putnam formulated a complementary argument based on what he called "functional isomorphism". He defined the concept in these terms: "Two systems are functionally isomorphic if 'there is a correspondence between the states of one and the states of the other that preserves functional relations'." In the case of computers, two machines are functionally isomorphic if and only if the sequential relations among states in the first are exactly mirrored by the sequential relations among states in the other. Therefore, a computer made out of silicon chips and a computer made out of cogs and wheels can be functionally isomorphic but constitutionally diverse. Functional isomorphism implies multiple realizability.^[25] This argument is sometimes referred to as an "a priori argument".^[24]

Jerry Fodor, Putnam, and others noted that, along with being an effective argument against type-identity theories, multiple realizability implies that any low-level explanation of higher-level mental phenomena is insufficiently abstract and general.^[25][26][27] Functionalism, which identifies mental kinds with functional kinds that are characterized exclusively in terms of causes and effects, abstracts from the level of microphysics, and therefore seemed to be a better explanation of the relation between mind and body. In fact, there are many functional kinds, such as mousetraps, software and bookshelves, which are multiply realized at the physical level.^[25]

Machine state functionalism[link]

A Turing machine can be visualized as an infinite tape of slots that are written or erased one at a time, with the choice of action determined by a "state". According to Putnam's machine-state functionalism, the notions of state in an abstract computer and mental state are essentially the same.

The first formulation of such a functionalist theory was put forth by Putnam himself. This formulation, which is now called "machine-state functionalism", was inspired by analogies noted by Putnam and others between the mind and theoretical "Turing machines" capable of computing any given algorithm.^[28]

In non-technical terms, a Turing machine can be visualized as an infinitely long tape divided into squares (the memory) with a box-shaped scanning device that sits over and scans one square of the memory at a time. Each square is either blank (B) or has a 1 written on it. These are the inputs to the machine. The possible outputs are:

• Halt: Do nothing.
• R: move one square to the right.
• L: move one square to the left.
• B: erase whatever is on the square.
• 1: erase whatever is on the square and print a 1.

A simple example of a Turing machine which writes out the sequence '111' after scanning three blank squares and then stopping is specified by the following machine table:

This table states that if the machine is in state one and scans a blank square (B), it will print a 1 and remain in state one. If it is in state one and reads a 1, it will move one square to the right and also go into state two. If it is in state two and reads a B, it will print a 1 and stay in state two. If it's in state two and reads a 1, it will move one square to the right and go into state three. Finally, if it is in state three and reads a B, it prints a 1 and remains in state three.^[29]

The point, for functionalism, is the nature of the "states" of the Turing machine. Each state can be defined in terms of its relations to the other states and to the inputs and outputs. State one, for example, is simply the state in which the machine, if it reads a B, writes a 1 and stays in that state, and in which, if it reads a 1, it moves one square to the right and goes into a different state. This is the functional definition of state one; it is its causal role in the overall system. The details of how it accomplishes what it accomplishes and of its material constitution are completely irrelevant.

According to machine-state functionalism, the nature of a mental state is just like the nature of the automaton states described above. Just as "state one" simply is the state in which, given an input B, such-and-such happens, so being in pain is the state which disposes one to cry "ouch", become distracted, wonder what the cause is, and so forth.^[30]

Rejection of functionalism[link]

In the late 1980s, Putnam abandoned his adherence to functionalism and other computational theories of mind. His change of mind was primarily due to the difficulties that computational theories have in explaining certain intuitions with respect to the externalism of mental content. This is illustrated by Putnam's own Twin Earth thought experiment (see Philosophy of language).^[11] He also developed a separate argument against functionalism in 1988, based on Fodor's generalized version of multiple realizability. Asserting that functionalism is really a watered-down identity theory in which mental kinds are identified with functional kinds, Putnam argued that mental kinds may be multiply realizable over functional kinds. The argument for functionalism is that the same mental state could be implemented by the different states of a universal Turing machine.^[31]

Despite Putnam's rejection of functionalism, it has continued to flourish and has been developed into numerous versions by thinkers as diverse as David Marr, Daniel Dennett, Jerry Fodor, and David Lewis.^[32] Functionalism helped lay the foundations for modern cognitive science^[32] and is the dominant theory of mind in philosophy today.^[33]

Philosophy of language[link]

Semantic externalism[link]

One of Putnam's contributions to philosophy of language is his claim that "meaning just ain't in the head". He illustrated this using his "Twin Earth" thought experiment to argue that environmental factors play a substantial role in determining meaning. Twin Earth shows this, according to Putnam, since on Twin Earth everything is identical to Earth, except that its lakes, rivers and oceans are filled with XYZ whereas those of earth are filled with H₂O. Consequently, when an earthling, Fredrick, uses the Earth-English word "water", it has a different meaning from the Twin Earth-English word "water" when used by his physically identical twin, Frodrick, on Twin Earth. Since Fredrick and Frodrick are physically indistinguishable when they utter their respective words, and since their words have different meanings, meaning cannot be determined solely by what is in their heads. This led Putnam to adopt a version of semantic externalism with regard to meaning and mental content.^[9][25] The late philosopher of mind and language Donald Davidson, despite his many differences of opinion with Putnam, wrote that semantic externalism constituted an "anti-subjectivist revolution" in philosophers' way of seeing the world. Since the time of Descartes, philosophers had been concerned with proving knowledge from the basis of subjective experience. Thanks to Putnam, Tyler Burge and others, Davidson said, philosophy could now take the objective realm for granted and start questioning the alleged "truths" of subjective experience.^[34]

Theory of meaning[link]

Putnam, along with Saul Kripke, Keith Donnellan, and others, contributed to what is known as the causal theory of reference.^[2] In particular, Putnam maintained in The Meaning of "Meaning" that the objects referred to by natural kind terms—such as tiger, water, and tree—are the principal elements of the meaning of such terms. There is a linguistic division of labor, analogous to Adam Smith's economic division of labor, according to which such terms have their references fixed by the "experts" in the particular field of science to which the terms belong. So, for example, the reference of the term "lion" is fixed by the community of zoologists, the reference of the term "elm tree" is fixed by the community of botanists, and the reference of the term "table salt" is fixed as "NaCl" by chemists. These referents are considered rigid designators in the Kripkean sense and are disseminated outward to the linguistic community.^[25]

Putnam specifies a finite sequence of elements (a vector) for the description of the meaning of every term in the language. Such a vector consists of four components:

1. the object to which the term refers, e.g., the object individuated by the chemical formula H₂O;
2. a set of typical descriptions of the term, referred to as "the stereotype", e.g., "transparent", "colorless", and "hydrating";
3. the semantic indicators that place the object into a general category, e.g., "natural kind" and "liquid";
4. the syntactic indicators, e.g., "concrete noun" and "mass noun".

Such a "meaning-vector" provides a description of the reference and use of an expression within a particular linguistic community. It provides the conditions for its correct usage and makes it possible to judge whether a single speaker attributes the appropriate meaning to that expression or whether its use has changed enough to cause a difference in its meaning. According to Putnam, it is legitimate to speak of a change in the meaning of an expression only if the reference of the term, and not its stereotype, has changed. However, since there is no possible algorithm that can determine which aspect—the stereotype or the reference—has changed in a particular case, it is necessary to consider the usage of other expressions of the language.^[25] Since there is no limit to the number of such expressions which must be considered, Putnam embraced a form of semantic holism.^[35]

Philosophy of mathematics[link]

Putnam made a significant contribution to philosophy of mathematics in the Quine–Putnam "indispensability argument" for mathematical realism.^[28] This argument is considered by Stephen Yablo to be one of the most challenging arguments in favor of the acceptance of the existence of abstract mathematical entities, such as numbers and sets.^[36] The form of the argument is as follows.

1. One must have ontological commitments to all entities that are indispensable to the best scientific theories, and to those entities only (commonly referred to as "all and only").
2. Mathematical entities are indispensable to the best scientific theories. Therefore,
3. One must have ontological commitments to mathematical entities.^[37]

The justification for the first premise is the most controversial. Both Putnam and Quine invoke naturalism to justify the exclusion of all non-scientific entities, and hence to defend the "only" part of "all and only". The assertion that "all" entities postulated in scientific theories, including numbers, should be accepted as real is justified by confirmation holism. Since theories are not confirmed in a piecemeal fashion, but as a whole, there is no justification for excluding any of the entities referred to in well-confirmed theories. This puts the nominalist who wishes to exclude the existence of sets and non-Euclidean geometry, but to include the existence of quarks and other undetectable entities of physics, for example, in a difficult position.^[37]

Putnam holds the view that mathematics, like physics and other empirical sciences, uses both strict logical proofs and "quasi-empirical" methods. For example, Fermat's last theorem states that for no integer Failed to parse (Missing texvc executable; please see math/README to configure.): n>2

are there positive integer values of x, y, and z such that Failed to parse (Missing texvc executable; please see math/README to configure.): x^n+y^n=z^n

. Before this was proven for all Failed to parse (Missing texvc executable; please see math/README to configure.): n>2

in 1995 by Andrew Wiles,[38] it had been proven for many values of n. These proofs inspired further research in the area, and formed a quasi-empirical consensus for the theorem. Even though such knowledge is more conjectural than a strictly proven theorem, it was still used in developing other mathematical ideas.[8]

Mathematics and computer science[link]

Putnam has contributed to scientific fields not directly related to his work in philosophy.^[2] As a mathematician, Putnam contributed to the resolution of Hilbert's tenth problem in mathematics. Yuri Matiyasevich had formulated a theorem involving the use of Fibonacci numbers in 1970, which was designed to answer the question of whether there is a general algorithm that can decide whether a given system of Diophantine equations (polynomials with integer coefficients) has a solution among the integers. Putnam, working with Martin Davis and Julia Robinson, demonstrated that Matiyasevich's theorem was sufficient to prove that no such general algorithm can exist. It was therefore shown that David Hilbert's famous tenth problem has no solution.^[13]

In computability theory, Putnam investigated the structure of the ramified analytical hierarchy, its connection with the constructible hierarchy and its Turing degrees. He showed that there exist many levels of the constructible hierarchy which do not add any subsets of the integers^[39] and later, with his student George Boolos, that the first such "non-index" is the ordinal Failed to parse (Missing texvc executable; please see math/README to configure.): \beta_0

of ramified analysis[40] (this is the smallest Failed to parse (Missing texvc executable; please see math/README to configure.): \beta
such that Failed to parse (Missing texvc executable; please see math/README to configure.): L_\beta
is a model of full second-order comprehension), and also, together with a separate paper with Richard Boyd (another of Putnam's students) and Gustav Hensel,[41] how the Davis–Mostowski–Kleene hyperarithmetical hierarchy of arithmetical degrees can be naturally extended up to Failed to parse (Missing texvc executable; please see math/README to configure.): \beta_0

.

In computer science, Putnam is known for the Davis-Putnam algorithm for the Boolean satisfiability problem (SAT), developed with Martin Davis in 1960.^[2] The algorithm finds if there is a set of true or false values that satisfies a given Boolean expression so that the entire expression becomes true. In 1962, they further refined the algorithm with the help of George Logemann and Donald W. Loveland. It became known as the DPLL algorithm. This algorithm is efficient and still forms the basis of most complete SAT solvers.^[12]

Epistemology[link]

A "brain in a vat"—Putnam uses this thought experiment to argue that skeptical scenarios are impossible.

In the field of epistemology, Putnam is known for his "brain in a vat" thought experiment (a modernized version of Descartes' evil demon hypothesis). The argument is that one cannot coherently state that one is a disembodied "brain in a vat" placed there by some "mad scientist".^[9]

This follows from the causal theory of reference. Words always refer to the kinds of things they were coined to refer to, thus the kinds of things their user, or the user's ancestors, experienced. So, if some person, Mary, were a "brain in a vat", whose every experience is received through wiring and other gadgetry created by the "mad scientist", then Mary's idea of a "brain" would not refer to a "real" brain, since she and her linguistic community have never seen such a thing. Rather, she saw something that looked like a brain, but was actually an image fed to her through the wiring. Similarly, her idea of a "vat" would not refer to a "real" vat. So, if, as a "brain in a vat", she were to say "I'm a brain in a vat", she would actually be saying "I'm a brain-image in a vat-image", which is incoherent. On the other hand, if she is not a "brain in a vat", then saying that she is still incoherent, but now because she actually means the opposite. This is a form of epistemological externalism: knowledge or justification depends on factors outside the mind and is not solely determined internally.^[9]

Putnam has clarified that his real target in this argument was never skepticism, but metaphysical realism.^[42] Since realism of this kind assumes the existence of a gap between how man conceives the world and the way the world really is, skeptical scenarios such as this one (or Descartes' Evil demon) present a formidable challenge. Putnam, by arguing that such a scenario is impossible, attempts to show that this notion of a gap between man's concept of the world and the way it is, is in itself absurd. Man cannot have a "God's eye" view of reality. He is limited to his conceptual schemes. Metaphysical realism is therefore false, according to Putnam.^[43]

Metaphilosophy and ontology[link]

In the late 1970s and the 1980s, stimulated by results from mathematical logic and by some ideas of Quine, Putnam abandoned his long-standing defence of metaphysical realism—the view that the categories and structures of the external world are both causally and ontologically independent of the conceptualizations of the human mind. He adopted a rather different view, which he called "internal realism".^[10][44]

Putnam renounced internal realism in his reply to Simon Blackburn in the volume Reading Putnam.^[45] The reasons he gave up his "antirealism" are stated in the first three of his replies in "The Philosophy of Hilary Putnam", an issue of the journal Philosophical Topics, where he gives a history of his use(s) of the term "internal realism", and, at more length, in his The Threefold Cord: Mind, Body and World (1999).^[46]

Internal realism was the view that, although the world may be causally independent of the human mind, the structure of the world—its division into kinds, individuals and categories—is a function of the human mind, and hence the world is not ontologically independent. The general idea is influenced by Kant's idea of the dependence of our knowledge of the world on the "categories of thought".^[47]

The problem with metaphysical realism, according to Putnam, was that it fails to explain the possibility of reference and truth. According to the metaphysical realist, our concepts and categories refer because they match up in some mysterious manner with the pre-structured categories, kinds and individuals that are inherent in the external world. But how is it possible that the world "carves up" into certain structures and categories, the mind carves up the world into its own categories and structures, and the two "carvings" perfectly coincide? The answer must be that the world does not come pre-structured but that structure must be imposed on it by the human mind and its conceptual schemes. In Reason, Truth, and History, Putnam identified truth with what he termed "idealized rational acceptability." The theory, which owes something to C.S. Peirce, is that a belief is true if it would be accepted by anyone under ideal epistemic conditions.^[10]

Nelson Goodman had formulated a similar notion in Fact, Fiction and Forecast in 1956. In that work, Goodman went as far as to suggest that there is "no one world, but many worlds, each created by the human mind."^[48] Putnam rejected this form of social constructivism, but retained the idea that there can be many correct descriptions of reality. No one of these descriptions can be scientifically proven to be the "one, true" description of the world. This does not imply relativism, for Putnam, because not all descriptions are equally correct and the ones that are correct are not determined subjectively.^[49]

Under the influence of C.S. Peirce and William James, Putnam also became convinced that there is no fact–value dichotomy; that is, ethical and aesthetic judgments often have a factual basis, while scientific judgments have an ethical element.^[49]

Neopragmatism and Wittgenstein[link]

At the end of the 1980s, Putnam became increasingly disillusioned with what he perceived as the "scientism" and the rejection of history that characterize modern analytic philosophy. He rejected internal realism because it assumed a "cognitive interface" model of the relation between the mind and the world. Under the increasing influence of James and the pragmatists, he adopted a direct realist view of this relation. For a time, under the influence of Ludwig Wittgenstein, he adopted a pluralist view of philosophy itself and came to view most philosophical problems as nothing more than conceptual or linguistic confusions created by philosophers by using ordinary language out of its original context.^[49]

Many of Putnam's most recent works have addressed the concerns of ordinary people, particularly their concerns about social problems.^[50] For example, he has written about the nature of democracy, social justice and religion. He has discussed the ideas of the continental philosopher, Jürgen Habermas, and has written articles influenced by "continental" ideas.^[14]

Criticism[link]

Putnam himself may be his own most formidable philosophical adversary.^[6] His frequent changes of mind have led him to attack his previous positions. However, many significant criticisms of his views have come from other philosophers and scientists. For example, multiple realizability has been criticized on the grounds that, if it were true, research and experimentation in the neurosciences would be impossible.^[51] According to Bechtel and Mundale, to be able to conduct such research in the neurosciences, universal consistencies must either exist or be assumed to exist in brain structures. It is the similarity (or homology) of brain structures that allows us to generalize across species.^[51] If multiple realizability were an empirical fact, results from experiments conducted on one species of animal (or one organism) would not be meaningful when generalized to explain the behavior of another species (or organism of the same species).^[52] Other criticisms of MR have been proposed by Jaegwon Kim, David Lewis, Robert Richardson and Patricia Churchland.^{[53][54][55][56]}

One of the main arguments against functionalism was formulated by Putnam himself: the Twin Earth thought experiment. However, there have been other criticisms. The Chinese room argument by John Searle (1980) is a direct attack on the claim that thought can be represented as a set of functions. The thought experiment is designed to show that it is possible to mimic intelligent action, without any interpretation or understanding, through the use of a purely functional system. In short, Searle describes a situation in which a person who speaks only English is locked in a room with Chinese symbols in baskets and a rule book in English for moving the symbols around. The person is instructed, by people outside the room, to follow the rule book for sending certain symbols out of the room when given certain symbols. Further, suppose that the people outside the room are Chinese speakers and are communicating with the person inside via the Chinese symbols. According to Searle, it would be absurd to claim that the English speaker inside "knows" Chinese based on these syntactic processes alone. This thought experiment attempts to show that systems that operate merely on syntactic processes cannot realize any semantics (meaning) or intentionality (aboutness). Thus, Searle attacks the idea that thought can be equated with the following of a set of syntactic rules. Thus, functionalism is an inadequate theory of the mind.^[57] Several other arguments against functionalism have been advanced by Ned Block.^[58]

Putnam has consistently adhered to the idea of semantic holism, in spite of the many changes in his other positions. The problems with this position have been described by Michael Dummett, Jerry Fodor, Ernest Lepore, and others. In the first place, they suggest that, if semantic holism is true, it is impossible to understand how a speaker of a language can learn the meaning of an expression, for any expression of the language. Given the limits of our cognitive abilities, we will never be able to master the whole of the English (or any other) language, even based on the (false) assumption that languages are static and immutable entities. Thus, if one must understand all of a natural language to understand a single word or expression, language learning is simply impossible. Semantic holism also fails to explain how two speakers can mean the same thing when using the same linguistic expression, and therefore how any communication at all is possible between them. Given a sentence P, since Fred and Mary have each mastered different parts of the English language and P is related differently to the sentences in each part, the result is that P means one thing for Fred and something else for Mary. Moreover, if a sentence P derives its meaning from its relations with all of the sentences of a language, as soon as the vocabulary of an individual changes by the addition or elimination of a sentence, the totality of relations changes, and therefore also the meaning of P. As this is a common phenomenon, the result is that P has two different meanings in two different moments in the life of the same person. Consequently, if I accept the truth of a sentence and then reject it later on, the meaning of that which I rejected and that which I accepted are completely different and therefore I cannot change my opinions with regard to the same sentences.^[59][60][61]

The brain in a vat argument has also been subject to criticism.^[62] Crispin Wright argues that Putnam's formulation of the brain-in-a-vat scenario is too narrow to refute global skepticism. The possibility that one is a recently disembodied brain in a vat is not undermined by semantic externalism. If a person has lived her entire life outside the vat—speaking the English language and interacting normally with the outside world—prior to her "envatment" by a mad scientist, when she wakes up inside the vat, her words and thoughts (e.g., "tree" and "grass") will still refer to the objects or events in the external world that they referred to before her envatment.^[42] In another scenario, a brain in a vat may be hooked up to a supercomputer that randomly generates perceptual experiences. In this case, one's words and thoughts would not refer to anything, and would therefore be devoid of content. Semantics would no longer exist and the argument would be meaningless.^[63]

In philosophy of mathematics, Stephen Yablo has argued that the Quine–Putnam indispensability thesis does not demonstrate that mathematical entities are truly indispensable. The argumentation is sophisticated, but the upshot is that one can achieve the same logical results by simply replacing all occurrences of the expression "so-and-so exists" (e.g., numbers exist) by occurrences of the expression "so-and-so is assumed (or hypothesized) to exist". For example, one can take the argument for indispensability described above and replace all references to existent entities with references to entities assumed to exist as follows.

1*. One must have ontological commitments to all and only the entities that are assumed to exist and are indispensable to the best scientific theories.

2*. Mathematical entities that are assumed to exist are indispensable to the best scientific theories. Therefore,

3*. One must have ontological commitments to mathematical entities that are assumed to exist.^[36]

Finally, Putnam's internal realism has been accused by Curtis Brown of being a disguised form of subjective idealism. If this is the case, it is subject to the traditional arguments against that position. In particular, it falls into the trap of solipsism. That is, if existence depends on experience, as subjective idealism maintains, and if one's consciousness were to stop existing, then the rest of the universe would stop existing as well.^[47]

Academic genealogy[link]

Major works[link]

• The "Innateness Hypothesis" and Explanatory Models in Linguistics, 1967.^[64]
• Philosophy of Mathematics: Selected Readings. Edited with Paul Benacerraf. Englewood Cliffs, N.J.: Prentice-Hall, 1964. 2nd ed., Cambridge: Cambridge University Press, 1983. ISBN 0-521-29648-X
• Philosophy of Logic. New York: Harper and Row, 1971. London: George Allen and Unwin, 1972. ISBN 0-04-160009-6
• Mathematics, Matter and Method. Philosophical Papers, vol. 1. Cambridge: Cambridge University Press, 1975. 2nd. ed., 1985 paperback: ISBN 0-521-29550-5
• Mind, Language and Reality. Philosophical Papers, vol. 2. Cambridge: Cambridge University Press, 1975. 2003 paperback: ISBN 0-521-29551-3
• Meaning and the Moral Sciences. London: Routledge and Kegan Paul, 1978.
• Reason, Truth, and History. Cambridge: Cambridge University Press, 1981. 2004 paperback: ISBN 0-521-29776-1
• Realism and Reason. Philosophical Papers, vol. 3. Cambridge: Cambridge University Press, 1983. 2002 paperback: ISBN 0-521-31394-5
• Methodology, Epistemology, and Philosophy of Science: Essays in Honour of Wolfgang Stegmüller. edited with Wilhelm K. Essler and Carl G. Hempel. Dordrecht: D. Reidel, 1983.
• Epistemology, Methodology, and Philosophy of Science: Essays in Honour of Carl G. Hempel. edited with Wilhelm K. Essler and Wolfgang Stegmüller. Dordrecht: D. Reidel, 1985.
• The Many Faces of Realism. La Salle, Ill.: Open Court, 1987. ISBN 0-8126-9043-5
• Representation and Reality. Cambridge, Mass.: MIT Press, 1988. ISBN 0-262-66074-1
• Realism with a Human Face. edited by James F. Conant. Cambridge, Mass.: Harvard University Press, 1990. ISBN 0-674-74945-6
• Renewing Philosophy. Cambridge, Mass.: Harvard University Press, 1992. ISBN 0-674-76094-8
• Pursuits of Reason: Essays in Honor of Stanley Cavell. edited with Ted Cohen and Paul Guyer. Lubbock: Texas Tech University Press, 1993. ISBN 0-89672-266-X
• Words and Life. edited by James F. Conant. Cambridge, Mass.: Harvard University Press, 1994. ISBN 0-674-95607-9
• Pragmatism: An Open Question. Oxford: Blackwell, 1995. ISBN 0-631-19343-X
• The Threefold Cord: Mind, Body, and World. New York: Columbia University Press, 1999. ISBN 0-231-10287-9
• Enlightenment and Pragmatism. Assen: Koninklijke Van Gorcum, 2001. 48pp.
• The Collapse of the Fact/Value Dichotomy and Other Essays. Cambridge, Mass.: Harvard University Press, 2002. Description. ISBN 0-674-01380-8
• Ethics Without Ontology. Cambridge, Mass.: Harvard University Press, 2002. ISBN 0-674-01851-6
• Jewish Philosophy as a Guide to Life: Rosenzweig, Buber, Levinas, Wittgenstein. Bloomington: Indiana University Press, 2008.
• Philosophy in an Age of Science. edited by Mario De Caro and David Macarthur. Cambridge, Mass.: Harvard University Press, forthcoming.

Works about Putnam[link]

• Y. Ben-Menahem (ed.), Hilary Putnam, Contemporary Philosophy in Focus, Cambridge University Press, Cambridge, 2005.
• P. Clark-B. Hale (eds.), Reading Putnam, Blackwell, Cambridge (Massachusetts)-Oxford 1995.
• C.S. Hill (ed.), The Philosophy of Hilary Putnam, Fayetteville, Arkansas 1992.
• M. Rüdel, Erkenntnistheorie und Pragmatik: Untersuchungen zu Richard Rorty und Hilary Putnam, (Dissertation) Hamburg 1987.
• Maximilian de Gaynesford Hilary Putnam McGill-Queens University Press / Acumen, 2006.

See also[link]

	Biography portal
	Logic portal

• American philosophy
• List of American philosophers
• Rietdijk–Putnam argument

Notes[link]