In this paper, I consider Richard Rufus’ account of generation and corrup- tion. This is a fundamental metaphysical question in the Aristotelian framework. Given that there are things that are corruptible (such as trees and cats and the human body), and things that are incorruptible (such as the celestial bodies and angels), what is it that makes one one, and the other the other? In other words, what is the ultimate explanation (in Rufus' terminology, the principle or principles) of corruptibility and incorruptibility? Do corruptible and incorruptible things have the same principles – the same fundamental metaphysical constitution – or are their principles different? Richard Rufus was among the first ones lecturing on Aristotle’s _Metaphysics_ at the University of Paris. He addresses these questions in book 4 (Gamma), lectio 1, question 2 of his longer commentary on Aristotle’s work (the _Scriptum_), which will provide the main textual basis of this paper. The other textual basis is an anonymous commentary on Aristotle’s _On generation and corruption_, found in Oxford, Corpus Christi MS 119, whose treatment of these issues is remarkably similar to Rufus’. As I show, we can learn a great deal about Rufus’ general metaphysical commitments by looking at this particular question, especially concerning his view of prime matter and his view of the qualities of the resurrected bodies.