Hume on What There Is

This paper argues that a neglected, in fact a barely noticed, concept in Hume’s A Treatise of Human Nature plays a crucial role in understanding his philosophy. The crucial concept arises in connection with the difficulty that Hume encounters in referring to the “external world.” Indeed, as Quine observes concerning Hume, if all that can be thought are our own ideas and impressions (viz. perceptions), then it is unclear how we can possibly think of objects that are not our own ideas and impressions. Hume writes: The farthest we can go toward a conception of external objects, when supposed specifically different from our perceptions, is to form a relative idea of them, without pretending to comprehend the related objects. Generally speaking, we do not suppose them specifically different; only attribute to them different relations, connections and durations (Hume, 17401, 1, 2, 6.19, 20 p. 49). The first purpose of this paper is to explain what Hume means by “relative ideas.” The second purpose is to explain their importance in Hume’s ontology, that is, his understanding of what there is. The third purpose is to consider Quine’s argument against Hume in his seminal paper “On What There Is.” Finally, the fourth purpose of the paper is to assess the role of relative ideas and in particular the relative idea of external existence in Hume’s ontology.