Abstract
Modalities enter into practically every area of contemporary philosophy. Great progress has been made in understanding the variety of differences between what is possible, what is actual, and what is necessary. But things were not always so clear. We owe a great debt in this area, as in so many others, to Aristotle, who had a lot to say on the topic, part of which comprises his discussion and use of the actuality/potentiality distinction. One important task in understanding his discussion of actuality and potentiality is locating the distinction within the wider area of modality in general. One very general area in which modalities are significant is the assessment of arguments. Aristotle provides us with the basics of a modal logic, and in Metaphysics V 12, treats the family of modal notions expressed by the Greek noun dunamis and its cognates. This article explores his account of energeia and dunamis, matter and substance, capacities, natures, and dispositions.