 Since its beginnings with Socrates, philosophy has typically involved the project of questioning the accepted knowledge of the day. Later, Locke, Hume, and especially, Kant developed a distinctively modern idea of philosophy as the critique of knowledge. Kant’s great epistemological innovation was to maintain that the same critique that revealed the limits of our knowing powers could also reveal necessary conditions for their exercise. What might have seemed just contingent features of human cognition (for example, the spatial and temporal character of its perceptual objects) turn out to be necessary truths. Foucault, however, suggests the need to invert this Kantian move. Rather than asking what, in the apparently contingent, is actually necessary, he suggests asking what, in the apparently necessary, might be contingent. The focus of his questioning is the modern human sciences (biological, psychological, social). These purport to offer universal scientific truths about human nature that are, in fact, often mere expressions of ethical and political commitments of a particular society. Foucault’s critical philosophy undermines such claims by exhibiting how they are the outcome of contingent historical forces, not scientifically grounded truths. Each of his major books is a critique of historical reason.