The nature of the Humean mind (David Hume)

David Hume's fundamental goal in Book One of his Treatise of Human Nature is to provide a general account of the content and operation of the human mind, grounded in "experience and observation." I argue that Hume is drawn to two incompatible models of the mind that are reflected in two famous metaphors he uses. Motivated by his empiricism, Hume famously concludes that the mind is nothing but a bundle of perceptions. This model of the mind is 'thin' because it banishes any appeal to objective causal relations, underlying processes, substances, or "real connections" among the mind's constituent perceptions. Motivated by the ambition to provide a scientific explanation of the mind's workings, Hume also appeals to what I call a 'thick model' of the mind, reflected in his republic metaphor. The republic metaphor compares the mind to a republic of individuals who are connected together by various relations and laws. The thick picture, accordingly, invokes real causal connections as well as unobserved faculties and processes to explain observed patterns among the mind's perceptions.; Prima facie, the thick and thin models are incompatible. The tension between them is most salient in Hume's discussion of personal identity. He appeals to causal relations in order to explain the apparent unity of perceptions within a particular mind. At the same time, he thins down his account by arguing that the causal relations are really only subjective associations among the related perceptions. I examine the nature of these associations and conclude that Hume's use of association presupposes a thick picture of the mind, which renders his explanation of mental unity circular. Hume's scientific agenda requires inferred as well as observed aspects of the mind, a persistent mind as well as a sequence of perceptions, and bona fide dependence among the perceptions as well as constant conjunction of perceptual types. Hume's theory of the mind is thus genuinely inconsistent. The inconsistency is generated by a philosophically important conflict between his understanding of science's explanatory goals and its empirical methods.