The Argument from Reason is an argument for the existence of God (at least as a supernatural instantiater of human reason) largely developed by C.S. Lewis.

C.S. Lewis originally posited the argument as follows:

The argument against materialism holds:

The argument for the existence of God holds:

The argument as stated is not strictly a proof of God's existence because it requires the assumption that humans can assess the truth or falsehood of claims or that humans can be convinced by argument. The assumption that humans can assess the truth or falsehood of claims is undeniable because its very denial requires one to assess the truth or falsehood of a claim, namely the assumption itself. The only possible alternatives are either to accept the claim or be content to accept or reject no claims whatsoever.^{[citation needed]} This argument fails to address the validity of human assessment. Assuming that all assessments of truth and falsehood made by humans are valid, and therefore rational. Moreover, the argument assumes panpsychism away as axiomatically false. Thus it is better not be thought of as a proof of God's existence, but as an attempt to disprove naturalistic materialism. Naturalistic materialism is the worldview held by most atheists and, therefore, the argument often is referenced as a proof of God's existence.

In logic and rhetoric, a fallacy is usually an improper argumentation in reasoning often resulting in a misconception or presumption. Literally, a fallacy is "an error in reasoning that renders an argument logically invalid". By accident or design, fallacies may exploit emotional triggers in the listener or participant (appeal to emotion), or take advantage of social relationships between people (e.g. argument from authority). Fallacious arguments are often structured using rhetorical patterns that obscure any logical argument.

Though an argument is not "logically valid", it is not necessarily the case that the conclusion is incorrect. It simply means that the conclusion cannot logically be arrived at using that argument.

Though often used unintentionally, fallacies can be used purposefully to win arguments regardless of the merits. Among such devices, discussed in more detail below, are: "ignoring the question" to divert argument to unrelated issues using a red herring, making the argument personal (argumentum ad hominem) and discrediting the opposition's character, "begging the question" (petitio principi), the use of the non-sequitur, false cause and effect (post hoc ergo propter hoc), bandwagoning (everyone says so), the "false dilemma" or "either-or fallacy" in which the situation is oversimplified, "card-stacking" or selective use of facts, and "false analogy". Another common device is the "false generalization", an abstraction of the argument that shifts discussion to platitudes where the facts of the matter are lost. There are many, many more tricks to divert attention from careful exploration of a subject.

Ayn Rand ( /ˈaɪn ˈrænd/; born Alisa Zinov'yevna Rosenbaum, February 2 [O.S. January 20] 1905 – March 6, 1982) was a Russian-American novelist, philosopher, playwright, and screenwriter. She is known for her two best-selling novels The Fountainhead and Atlas Shrugged and for developing a philosophical system she called Objectivism.

Born and educated in Russia, Rand moved to the United States in 1926. She worked as a screenwriter in Hollywood and had a play produced on Broadway in 1935–1936. After two initially unsuccessful early novels, she achieved fame with her 1943 novel The Fountainhead. In 1957, she published her best-known work, the philosophical novel Atlas Shrugged. Afterward she turned to nonfiction to promote her philosophy, publishing her own magazines and releasing several collections of essays until her death in 1982.

Rand advocated reason as the only means of acquiring knowledge and rejected all forms of faith and religion. She supported rational and ethical egoism, and rejected ethical altruism. In politics, she condemned the initiation of force as immoral and opposed all forms of collectivism and statism, instead supporting laissez-faire capitalism, which she believed was the only social system that protected individual rights. She promoted romantic realism in art. She was sharply critical of the philosophers and philosophical traditions known to her besides Aristotle.

David Hume (7 May [O.S. 26 April] 1711 – 25 August 1776) was a Scottish philosopher, historian, economist, and essayist, known especially for his philosophical empiricism and scepticism. He was one of the most important figures in the history of Western philosophy and the Scottish Enlightenment. Hume is often grouped with John Locke, George Berkeley, and a handful of others as a British Empiricist.

Beginning with his A Treatise of Human Nature (1739), Hume strove to create a total naturalistic "science of man" that examined the psychological basis of human nature. In stark opposition to the rationalists who preceded him, most notably Descartes, he concluded that desire rather than reason governed human behaviour, saying: "Reason is, and ought only to be the slave of the passions." A prominent figure in the sceptical philosophical tradition and a strong empiricist, he argued against the existence of innate ideas, concluding instead that humans have knowledge only of things they directly experience. Thus he divides perceptions between strong and lively "impressions" or direct sensations and fainter "ideas", which are copied from impressions. He developed the position that mental behaviour is governed by "custom"; our use of induction, for example, is justified only by our idea of the "constant conjunction" of causes and effects. Without direct impressions of a metaphysical "self", he concluded that humans have no actual conception of the self, only of a bundle of sensations associated with the self.