Descartes holds that when you perceive something with perfect clarity, you are compelled to assent and cannot doubt. (This is a psychological claim.) Many commentators read him as endorsing Psychologism, according to which this compulsion is a matter of brute psychological force. I show that, in Descartes’s view, perfect clarity provides a reason for assent—indeed a perfect reason, which precludes any reason for doubt. (This is a normative claim.) Furthermore, advancing a view I call Rational Force, he holds that the (...) normative claim explains the psychological one: since your will is naturally responsive to reasons, you are compelled to assent because you have a perfect reason to assent. This coheres with his view that will is essentially active, self-determined, and free. The force that clarity exerts on the will is not the brute push of an efficient cause, but the rational pull of a final cause. (shrink)

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)

Descartes’s cogito – I am thinking, therefore I am – is an intuitive deduction. Contrary to Transparency, certainty of I am thinking does not come easily; it’s achieved by making introspection perfectly clear through radical doubt. Scientia – rational immunity to doubt – comes with the habit of intuiting with perfect clarity that skepticism is false. (This is the second of two companion entries; the prequel is called, "Descartes's Clarity First Epistemology.").

This article examines how deduction preserves certainty and how much certainty it can preserve according to Descartes’s Rules for the Direction of the Mind. I argue that the certainty of a deduction is a matter of four conditions for Descartes. First, certainty depends on whether the conjunction of simple propositions is composed with necessity or contingency. Second, a deduction approaches the certainty of an intuition depending on how many “acts of conceiving” it requires and—third—the complexity or difficulty of the acts (...) of thinking, which is determined by the content of the thoughts and on external factors. Fourth, certainty depends on the intellectual aptitude of the person using the deduction. A deduction lacks certainty when it relies on memory such that it is not apprehended with immediacy. However, the mental capacity and speed of a mind can be increased by training the special mental faculties of perspicacity and discernment. Increasing one’s intellectual aptitude allows for more steps of a deduction to be inferred in fewer acts of conceiving, thereby helping preserve the certainty of a deduction. (shrink)