“The imagination, according to my own confession, [is] the ultimate judge of all systems of philosophy.” So writes David Hume in A Treatise of Human Nature (T 1.4.4.1). But how can the imagination, of all things, be the ultimate judge of systems of philosophy? And how can Hume’s granting of this august judicial role to a faculty generally regarded as the source of whimsy and error be reconciled with his confidence, expressed in the Introduction to the Treatise,  that he is proposing in his own philosophy a “complete system” that is built on a “solid foundation” (T Intro. 6-7)? Those are the central questions that I propose to address. My answer to the first question will be that the Humean imagination serves as the ultimate judge of systems of philosophy chiefly by being, through what I will call its sense of probability, the sole judge of the probability that they are true. My answer to the second will be that, on Hume’s view, a system with sufficient probability of being true, as judged by the imagination, can properly be regarded as well-founded.

 

I will begin by explaining Hume’s general approach to those abstract ideas that are derived from a sense—that is, what we would now be likely to call response-dependent concepts—and examining the applicability of that general approach to the specific abstract idea of probability. I will then set out what I take to be his general approach to normative ideas and examine the applicability of that approach to the specific abstract idea of probable truth. Combining the results of these two investigations will allow us to see his abstract idea of probable truth as a concept that is both response-dependent and epistemically normative. We will then be in a position to understand the imagination’s use of that concept in properly judging systems of philosophy—including, of course, Hume’s own system. I will conclude by drawing several consequences for Humean epistemology and its relation to skepticism.