Aquinas on Change Actuality, Tense and Time in Thomas Aquinas’ Philosophy of Nature

This dissertation includes an introduction, five main chapters, and a conclusion. In the chapter “The Definition of Change” (2), I expound Aquinas’ account of change. I maintain that Aquinas’ account is meant to describe both spiritual and material changes. Hence, the hylomorphic account of change as the passage from form-less matter to enformed matter is unable to describe all changes. Contrary to Brower (2014), I suggest that Aquinas’ favorite model involves a passage from potentiality to actuality. In addition, I state that ‘change’ is identical to the second potentiality/first actuality of a process that includes three steps, a first potentiality, a second potentiality (or first actuality), and a second actuality. In the chapter on “Aquinas, Presentism, and Adverbialism” (3), I analyze the semantics of propositions that describe changing processes. I maintain that Aquinas subscribed to the view that past and future tense statements can have a truth-value. Chapter 4 (“Aristotle and Aquinas on the Principle of Plenitude”) is devoted to the so-called principle of plenitude, i.e. the thesis that all possibilities are realized at some point in the future. Aquinas is believed to have subscribed to the principle, whereas Aristotle’s texts are much more disputed. In this chapter, I offer a new interpretation, according to which Aristotle accepted a restricted version of the principle of plenitude, but Aquinas rejected the principle in all its formulations. In chapter 5 “Aquinas on Future Contingents”, I expound Aquinas’ theory of future contingents events. In this chapter, I make two claims. I state that Aquinas’ theory entails that future events do not exist, according to the ‘actual’ sense of existence. My second claim is about the logic of future contingents. I claim that Aquinas’ argument is logically sound, but presupposes that the so-called K-formula is not a tautology of Aquinas’ modal system. In chapter 6 I expound Aquinas’ definition of time. I maintain that Aquinas’ definition is not circular and time is distinct in both definition and in essendo from change. I conclude by stating that time has extra-mental existence.