 Descartes is often taken to be the paradigm of a classical foundationalist. Determined to build knowledge on appropriate and secure foundations, he seemed to want to identify foundational knowledge with infallible belief (though there is another interpretation that we’ll turn to in the next section, one that identifies foundational knowledge with infallible justification). Implicitly or explicitly, others seemed to follow his lead by restricting foundationally justified beliefs to beliefs that cannot be mistaken. Following Lehrer (1974: 81) we might formulate the following definition of infallible belief: S’s belief that P at t is infallible if S’s believing P at t  entails[4]  that P is true.