Alexander of Aphrodisias, Dialectic, and the First Principles of Science

Alexander of Aphrodisias’ Commentary on the Topics tackles a thorny issue in Aristotelian scholarship: the place of dialectic in inquiries about the first principles of science. The commentary offers several dialectical syllogisms whose conclusions are first principles of geometry (namely, the definitions of point, line, and surface). However, by themselves, his examples do not clarify the epistemic strength of these dialectical syllogisms. I argue that, for Alexander, preconceptions furnish us with a subset of premises that warrant the truth of conclusions reached on their basis, and that the content of preconceptions can be used as accredited opinions ( endoxa ).