Abstract

Hume establishes a link between our capacity to conceive or form “clear and distinct ideas” and metaphysical possibility. Hume’s so-called Conceivability Principle is usually assumed to be epistemic: conceivability is supposed to inform us of independent metaphysical facts. In this chapter, however, I argue that Hume is not engaged in modal epistemology. For Hume, there is no epistemic relation between conceivability and an independent metaphysical world of possibilities. On my reading, conceivability is more like the “mètre étalon” in Paris—the standard unit of measurement of length—than a window or telescope into some metaphysical world. Conceivability is the standard of metaphysical possibility. And just as the meter is defined as a certain distance of light traveled, for Hume, conceivability is defined in terms of the liberty of the imagination. I discuss how Hume deploys conceivability along with knowledge—the standard of metaphysical necessity—as tools for measuring or assessing the alleged metaphysical necessity of a cause to every beginning of existence and the alleged rational foundation of causal inferences.