During the early modern period, a framework broadly attributable to Descartes sought to establish all knowledge on a foundation of indubitable truths that are fully clear and totally certain: intuitions. A powerful challenge to treating these seemingly unassailable intuitions as epistemic foundations is that the only truths which can be known in this fashion are so obvious and useless that they could not produce any other knowledge. Rationalists typically respond to this worry by maintaining that there are substantive intuitive truths. (...) Other natural options are to maintain that tautologous truths can serve as a fit foundation, or to reject this framework entirely. Empiricists like Locke, Hume, Condillac, and Mill opt for these other solutions. While Locke and Hume offer views that revise and refine this framework, Condillac and Mill engage in more radical departures from it. An interesting result of this difference in approach is that we see Locke and Hume subdividing reason between two domains – one in which intuition reigns, and one which is more properly the domain of the senses – while in Condillac and Mill we see two differing approaches – analysis and induction, respectively – to unifying all human reasoning within a single domain. (shrink)