We begin by reacquainting ourselves with the distinction between impressions and ideas. In the course of doing so, we examine impressions of sensation vs. impressions of reflection, simple vs. complex reflections and memory vs. imagination. Although these distinctions are fairly straightforward, they are not without controversy. One commentator has even suggested that Hume's distinction between impressions and ideas is "idio[tic]" (Bennett 1971, p. 225). Another scholar, being a bit more generous, finds it "not very plausible" (Stroud 1977, p. 28). However, if we realize that Hume is primarily engaged in a psychological, naturalistic project we see that these accusations are misplaced (where by "naturalistic' I simply mean empirical).