The chapter ‘Alexander of Aphrodisias on Concepts’ by Frans A. J. de Haas takes up another aspect of concept theory, that is, the endeavour to define what a concept is. Furthermore, he explores the interactions between the Peripatetics and the Stoics, as they are evidenced by Alexander, on ontological as well as psychological and epistemological issues. De Haas also offers a systematic study of part of Alexander’s rich vocabulary denoting concepts, thoughts, and universals, and of a correspondingly rich collection of verbs referring to the human activities of abstracting or constructing concepts. Importantly, this analysis sheds light on Alexander’s understanding of ennoia and noêma, and on Alexander’s views concerning the epistemic reliability of concepts and the unity of concepts in the human soul.

This chapter begins with an etymological and historical elucidation of the terms conscientia and synderesis. Philosophical and theological reflection on these terms, beginning with St. Jerome and proceeding through thinkers such as Peter Lombard and Philip the Chancellor, constitutes the background against which St. Thomas Aquinas develops his understanding, not only of conscientia and synderesis, but also of objective right (ius) or rights. Much of the debate regarding synderesis, the infallible basis of conscientia, concerns whether it is a power or habitus. Aquinas settles on understanding synderesis as a ‘habit’ of the potential intellect – which, following Aristotle, he understands as a sort of ‘blank slate’ upon which things can be written. One of the things written on the habit of synderesis is the practical version of the principle of non-contradiction: ‘good is to be done and pursued, evil avoided’. This allows him to develop a theory according to which objective rights are primary, although not to the exclusion of subjective rights. It also allows those in agreement with Aquinas to exclude subjective rights that contradict established objective rights.