Synderesis, the intellectus principiorum of practical reason according to Thomas Aquinas

Abstract

This study is an investigation on the theory of the first principles of practical reason in Thomas Aquinas. At the center of the theory stays the term “synderesis”, whose content was developed in discussions of medieval philosophy and theology, departing from its mention in Jerome’s Gloss to Ezekiel. This term indicates a concept that presents a new aspect in the moral action theory as compared with Aristotle’s ethics. After all, Thomas Aquinas understands it as the habit of the first principles of morals, which is equivalent to Aristotle’s habit of the first theoretical principles. Thus, the purpose is to understand how the concept of synderesis is received and developed in Thomas Aquinas’s moral philosophy by analyzing the three traditional issues: its nature, its infallibility, and its extinction.