Leibniz's Law & Philosophy of Mind (Frank Jackson)

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• published: 16 May 2015
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We draw some metaphysical conclusions about colour and belief from some epistemological commonplaces. It turns out that this requires us to challenge orthodoxy on the causal efficacy of mental properties and to rewrite the standard argument against dualism, but in a way which is good news for functionalists about the mind. Under what conditions is P evidence for Q? A comprehensive answer to that question is hard and inevitably controversial. We can however say three things that are, it seems to me, uncontroversial. Whether or not P is evidence for Q depends on (1) what P is, (2) what Q is, and (3) the background evidence. The details of how one might enlarge on these three observations will inevitably be controversial but the basic thought behind each is close to a truism. The talk is about how to deploy these observations, along with some equally commonsensical observations about when we are entitled to believe that one or another property is instantiated, to reach conclusions in the philosophy of mind on subjects that have been much debated. You might describe this as an exercise in using the noncontroversial to adjudicate the controversial. I expect that it will, in its turn, be controversial. Much of the argumentation will employ Leibniz’s law in epistemic contexts. I know from experience that this worries people. We all know that epistemic contexts are opaque. This, perhaps understandably, suggests that using Leibniz’s law in epistemic contexts involves a fallacy of the famous masked man variety. This means it is sensible (essential?) to take a moment to review why it is fine to use Leibniz’s law in epistemic contexts. Our review will be conducted as a short commentary on an issue that Quine most especially put on the table many years ago.