 Whether or not David Hume (1711–1776) learned from Collier, he learned a great deal from Berkeley, above all his empiricist epistemology, but for the most part he tried to avoid Berkeley’s outright commitment to idealism. Hume’s view that our knowledge consists of our ideas, our recognition of “philosophical” relations among them, such as identity and difference, and our recognition of “natural” relations among them such as causation, which are established by imagination and custom, could constitute an epistemological ground for idealism—causality, in particular, which Hume regards as the basis of all our knowledge of existence, is at the same time reduced to a way of feeling and thinking, in other words a state of mind. But depending on how he is read, Hume either accepts the skepticism about possible external objects that Berkeley tries to avoid with his ontology that renders any external objects other than other human or divine minds impossible, or else holds that even if there are valid arguments for skepticism it is psychologically impossible for human beings to remain in a skeptical frame of mind, thus we naturally even if not rationally believe in the existence of objects apart from our ideas of them. However, in those passages, prominently in Book I, Part IV of his early Treatise of Human Nature (1739–40), where Hume entertains a kind of monism that sees both “minds” and “objects” as nothing but different sets or “bundles” of one sort of thing, namely, perceptions, impressions and their paler copies, ideas, his position might seem much like Berkeley’s idealism, with the difference that while he reduces all reality to mental states like impressions and ideas he does not see these as properties that must inhere in substantial minds any more than in substantial bodies, both of which are fictions that we introduce in order to explain continuities among those impressions or ideas (although it may be difficult to explain who is introducing those fictions without resorting to substantial minds after all).