Natural Instinct, Perceptual Relativity, and Belief in the External World in Hume's <i>Enquiry</i>

In part 1 of Enquiry 12, Hume presents a skeptical argument against belief in external existence. The argument involves a perceptual relativity argument that seems to conclude straightaway the double existence of objects and perceptions, where objects cause and resemble perceptions. In Treatise 1.4.2, Hume claimed that the belief in double existence arises from imaginative invention, not reasoning about perceptual relativity. I dissolve this tension by distinguishing the effects of natural instinct and showing that some of these effects supplement the Enquiry's perceptual relativity argument. The Enquiry's skeptical argument thus reveals the fundamental involvement of natural instinct in any belief in external existence.