 David Hume in effect denies that a deduction can be provided for a number of metaphysical concepts – ideas, in his terminology – including the ideas of personal identity, of identity over time more generally, of the self as a subject distinct from its perceptions, and of causal power or force (1739, 1748). In Hume’s view, a concept can only be validated by finding a sensory experience, that is, an impression, in particular the one that is the ‘original’ of that idea, which must resemble that idea. But because, for example, any attempt to find an impression of causal power turns out to be fruitless, Hume concludes that this idea does not legitimately apply (1748: §7). In Kant’s terminology, Hume is determining whether one might provide an empirical deduction of the concept of causal power (A85/B117), and from the failure of the attempt to do so, he concludes that this concept lacks objective validity, that is, it does not apply to the objects of our experience.