Abstract

David Owen’s new book invites us to take a fresh look at three major modern philosophers: Descartes, Locke, and Hume. Although Leibniz invented the familiar conception of proof as a formal relationship among sentences, reasoning for these three philosophers was a very different animal: they thought of it as a matter, not of form, but of content. They regarded proof—demonstration or demonstrative reasoning—as a process of stringing together chains of relations between ideas. That process appeals to the content of the ideas involved, and is thus a radically non-formal conception of reasoning, one that has as little to do with the syllogisms of Aristotle and the Scholastics as it does with the post-Fregean notion of deductive validity dominant today.