When premises cannot be traced to self-evident principles, the argument is dialectical rather than demonstrative

This sort of foundationalist, infallibilist theory of knowledge is now thought of as Cartesian, but Descartes is simply following the Aristotelian tradition for which Aquinas became the preeminent spokesman. For Aquinas himself, however, the account just described serves as an aspirational ideal rather than a description of something we have actually attained. In practice, even where we have demonstrative knowledge, we usually cannot trace the principles all the way back to ultimate first prin