The Origin of the First Principles according to Thomas Aquinas. An interpretative Problem

Abstract

In the first book of his Commentary on Posterior Analytics, Thomas Aquinas explains that every demonstration assumes the existence of evident and indemonstrable principles which guarantee the certainty of the conclusions. To ensure the existence of certain and indemonstrable truths, Aquinas introduces the idea of per se notae propositions. These propositions are typically characterized by the fact that they have a predicate which is part of the intelligible content of the subject, in other words, they are analytic propositions. However, at the end of the second book, when Thomas explains how the principles of demonstrations are obtained, the doctrine exposed does not seem to be perfectly consistent with the doctrine of the per se notae propositions, because it describes a process of induction more suitable to explain the rise of non-analytic propositions. The aim of this paper is to propose a solution to this problem, through the distinction of two kinds of principle. It will be demonstrated the appropriateness of such a distinction by the discussion of some texts of Robert Grosseteste and Albert the Great.