Adequate Ideas and Modest Scepticism in Hume's Metaphysics of Space

In the Treatise of Human Nature, Hume argues that, because we have adequate ideas of the smallest parts of space, we can infer that space itself must conform to our representations of it. The paper examines two challenges to this argument based on Descartes's and Locke's treatments of adequate ideas, ideas that fully capture the objects they represent. The first challenge, posed by Arnauld in his Objections to the Meditations, asks how we can know that an idea is adequate. The second challenge, implicit in Locke's Essay, asks how an empiricist can characterize an idea as inadequate, as both picking out an object and yet failing to capture it fully. In showing how Hume responds to these challenges, his theory of perceptual representation is explained and his treatment of space is related to his scepticism. His conclusion is shown not to be a characterization of space as it exists wholly apart from our powers of conception. Instead, in an adumbration of Kant, his claim is restricted to space as it appears to us.