This paper deals with the question whether eternal activities are the exercises of capacities (dynamis) according to Aristotle, and if so, of what kind of capacities---capacities with just one possible outcome or capacities with two possible outcomes. This is a crucial issue for Aristotle. He mainly discusses this topic in Metaphysics IX 8, 1050b6-28. It is at the heart of his physical and metaphysical studies. It has consequences for understanding motion, the role of the unmoved movers, his ontology of capacities and his arguments for the priority of actuality. Because of the importance of this topic, many interpreters have dedicated intensive studies to the interpretation of the relevant passages (for instance, Makin (2006), Beere (2009), Frey (2015), Judson (2016)). Unfortunately, the results of these investigations are very diverse, in many cases contradicting each other.

I will mainly discuss Aristotle's account of eternal activities in Metaphysics IX 8, 1050b6--28. In brief, Aristotle argues in this passage that eternal activities cannot have underlying capacities because this would imply their perishability. He then draws a distinction between capacities for being without qualification (= for existence and/or essential being) and capacities for being with qualification (capacities for being as regards place, capacities for being as regards quality etc.) (Metaph. IX 8, 1050b13--18). He denies that eternal substances have capacities for being without qualification, but he allows them to have capacities for being in some respect. In particular, he claims that the heavenly bodies are moved in accordance with a `capacity for whence and whither'. So even though Aristotle just seems to have given an argument for the view that eternal activities cannot have underlying capacities, he is now ready to ascribe a `capacity in respect of whence and whither' to the eternal motion of the heavenly spheres.

Interpreters disagree on how we should understand this `capacity in respect of whence of whither'. All parties try to give an account of this kind of capacity that is not in conflict with Aristotle's argument according to which eternal activities cannot have any underlying capacities. Some argue that it is only a capacity for part of the itinerary. Others argue that it is a capacity for the entire eternal itinerary.

I argue that this `capacity for whence and whither' is what Aristotle calls in other places `topical matter' (hyle topikê). So far, interpreters have neglected Aristotle's discussion on topical matter in the Metaphysics and the De Caelo. I argue that by taking into account Aristotle's discussions in these passages we will be able to resolve the current interpretative difficulties of Metaphysics IX 8.