Hume on the Prospects for a Scientific Psychology

In Section One of an Enquiry Concerning Human Understanding, Hume distinguishes between two sorts of writing on human nature: first, one that appeals to common sense to make virtue seem attractive and, second, one that attempts to describe the principles governing the mind. Hume's defence of the second approach is in part a defence of the possibility of scientific psychology. Within the second approach, he distinguishes two parts: first, a descriptive branch he calls 'mental geography' and, second, a branch he compares to Newton's project in astronomy. In his defence of mental geography, Hume sketches an account of his method of enquiry in psychology. Common sense describes some basic faculties, philosophers can make finer distinctions within these, and introspection allows us to reliably describe ground-level processes. Hume's vision of Newtonian psychology is one that appeals to laws and forces and finds the hidden springs of the mind. His attempt to explain causal inference by appealing to the transfer of vivacity across associated perceptions in Part 2 of Section 5 is an attempt at Newtonian psychology: it's speculative, explanatory, and enunciates a putative psychological law.