Hume's Functionalism About Mental Kinds

A very common view of Hume’s distinction between impressions and ideas is that it is based on their intrinsic properties; specifically, their force and vivacity. Some interpreters have challenged this,one being David Landy (Landy 2006). He argues that for Hume the difference lies instead in the fact that impressions are not copies of anything, while ideas are copies of impressions. I regard this view as unsatisfactory, not because it is fundamentally mistaken but because (to put it in Humean terms) it “…it discovers not all the truth” (Treatise 1.3.7.4). I will argue that Hume was a functionalist about (some)mental kinds, individuating impressions, ideas, and beliefs (and possibly other mental phenomena) in terms of their causal role in our mental economy. The distinction between impressions and ideas involves the fact that ideas are copies and impressions are not, but also more than that. I will also argue that interpreting Hume as a functionalist enables one to make sense of a passage that is impossible to explain on the force-and-vivacity view, and that it does so more readily than Landy’s view.Furthermore, I think this interpretation makes better sense of Hume’s “missing shade of blue” than Landy’s does.