Hume\u27s Of scepticism with regard to reason

The arguments in “Of scepticism with regard to reason” get their start from Hume’s claim that, thanks to our “fallible and uncertain faculties,” we must “check” any present judgment from reason in a step of corrective reasoning (T 1.4.1.1; SBN 180). A corrective step is meant to “correct and regulate” present judgments from reason through reflection on past judgments from reason (T 1.4.1.5; SBN 181-82). Hume argues that this ushers in the extinction of knowledge and belief because reflection on past judgments will inevitably diminish our assurance for any present judgment. Why Hume thinks diminishment is inevitable has remained elusive. The key, I contend, is that our assurance for judgments diminishes because of what must be presupposed in order to make and accept them. Explicit consideration of the possibility that our present reasoning is mistaken would keep us from making or accepting any present judgment from reason. So to reach any judgment by reasoning, we must presuppose that we are reasoning legitimately, that is, from the right evidence and in the right way. Past judgments from legitimate reasoning are evidence that this presupposition is true while past judgments from erroneous reasoning are evidence that it’s false. Because legitimacy must be presupposed, the former evidence is accounted for in any present reasoning while the latter evidence is not. Accordingly, past errors afford unaccounted-for evidence that, when explicitly considered in a corrective step, can only diminish our present assurance. However, to stand pat with respect to a corrected judgment is to presuppose that it has been reached by legitimate reasoning. Past errors are evidence that this presupposition is false and that we’ve made the wrong corrected judgment. This prompts further reflection, which leads to further diminishment, which prompts further reflection, and so on until our first assurance is diminished to nothing—hence the extinction of knowledge and belief. Thus, Hume’s skeptical conclusions follow from reflecting on past judgments in successive corrective steps because the legitimacy of our present reasoning must be presupposed in order to make and accept any present judgment from reason