Choosing and Acting (Thomas Aquinas, Summa theologiae, Part I–II, Question 13, Article 2)

Abstract

In question 13, article 2, of part I–II of the Summa theologiae, Thomas Aquinas addresses the question of whether nonhuman animals are capable of making a ‘choice’ (electio). Since he adopts Aristotle’s definition of choice as the capacity to find the right means to an end, it seems, at first, as if various cases of animal behaviour show exactly that animals often do things on a means-to-end basis, and hence are capable of making a choice. However, Aquinas emphasises that we should be more careful in interpreting animal behaviour as voluntary, because even though animals seem to make rational choices – as he demonstrates with Sextus Empiricus’ famous example of Chrysippus’ dog – we should rather account for their behaviour by what he calls ‘sensory appetite’ (appetitus sensitivus). This does not mean that Aquinas considers animals to be simple machines (although he interestingly compares their behaviour to the behaviour of clocks and other artefacts). Rather, he wants to point out that (sometimes) even complex phenomena can be explained by simple processes.