Jiayu Zhang

Why does Aristotle commit to the existence of simple bodies? Why does Aristotle conduct an investigation into simple bodies as part of his his natural philosophy? These are the two questions I want to focus on in this dissertation. The answer to these questions, in my view, can be found in Aristotle's investigations into simple bodies in De Caelo and De Generatione et Corruptione. On the basis of my interpretation of these two treatises, I argue in this dissertation that Aristotle's investigation into simple bodies contributes significantly to his explanation of change, and amounts to a single, coherent, systematic account, based in first principles, of all change. Chapter 1 argues that Aristotle?s investigation of simple bodies in De Caelo is conducted through a cosmic method. This method, as I argue, is for the sake of the completeness and systematicity of his investigation of simple bodies. More specifically, I argue that, only if Aristotle's investigation of simple bodies is conducted in a cosmological background, can he put forward a systematic investigation of an exhaustive list of the fundamental components of all possible physical things in the universe. Chapter 2 argues that, in De Caelo I.2, the introduction and differentiation of simple bodies is achieved entirely by differentiating simple motions, and that Aristotle's aim in De Caelo I.2 is to provide an explanatory account of all possible locomotion. This contradicts the traditional interpretation of De Caelo I.2, which considers how, and how completely, Aristotle uses the differentiation of simple magnitudes to differentiate simple bodies, and which assumes that he introduces the notion of a simple body independently of the notion of a simple motion. This is why Aristotle identifies simple bodies with the fundamental components of the universe. Chapter 3 argues that the simple body that is neither heavy nor light (ether) is excluded from the field of generation and corruption, so that it does not contribute to Aristotle's explanation of the changes other than locomotion by forming the physical things that are subject to these changes. I argue that the exclusion of ether from the field of generation and corruption is necessary for his overall explanation of the changes other than locomotion, because it leads to the conclusion that only the sublunary simple bodies constitute the corruptible physical things and, in this way, contribute to Aristotle's explanation of the changes other than locomotion. Chapter 4 argues that Aristotle's investigation of simple bodies in De Caelo contains a rigorous deduction according to which the number of the sublunary simple bodies is ultimately settled. My reconstruction of this deduction is a refutation of the traditional view, according to which Aristotle has not provided sufficient reasons for the existence of four sublunary simple bodies in De Caelo. On the basis of my reconstruction of Aristotle?s deduction of simple bodies in De Caelo, it can be answered what are the simple bodies that are going to contribute to Aristotle's explanation of change. Chapter 5 argues that the reason why Aristotle moves from his characterization of simple bodies in De Caelo to that in GC is that his characterization of simple bodies in De Caelo is insufficient to support his view that the changes other than locomotion, especially generation and corruption, are everlasting. I argue against the traditional view, which says that Aristotle introduces a new characterization of simple bodies in GC because his characterization of simple bodies in De Caelo cannot differentiate simple bodies into four groups sufficiently. I argue that it is for the sake of providing us with an explanation of the changes other than locomotion that Aristotle moves on to his characterization of simple bodies in GC from that in De Caelo. Chapter 6 investigates why simple bodies have to be investigated in GC, and argues that this is because the matter of physical things comes to be from the mixture of simple bodies. While something like this view has been recognized in regard to Metaphysics Θ, I argue that this distinction is defended in Aristotle's theory of mixture in GC. This account of the way in which matter comes to be from simple bodies will significantly contribute to our interpretation of Aristotle's explanation of change. Chapter 7 explains, on the basis of Physics I and GC I, how simple bodies contribute to Aristotle's explanation of changes by forming the matter of physical things. I argue that, only if there is such matter, can the possibility of the substantial changes and the distinction between the substantial changes and other changes be explained. I conclude that, for Aristotle, change cannot be sufficiently explained without his commitment to the existence of simple bodies.

This paper argues that the four elements exist in different ways in mixtures and homogenous parts of substances. According to Aristotle’s definition in De caelo, the elements exist in virtue of themselves in the compound bodies which they compose. However, if we assume that they exist in the same way in hylomorphic compounds as they exist in the compound bodies which they directly compose, a discrepancy arises between Aristotle’s definition of element and his hylomorphic theory, because the elements cannot exist potentially, on the one hand, as the elements themselves, and, on the other hand, as the matter of a hylomorphic compound, at the same time. To solve this problem, homogenous bodies have been distinguished into mixtures and homogenous parts of hylomorphic individuals. According to Aristotle, it is only in mixtures that the elements exist in potentiality, while in the formation of the homogenous parts of a new substance generated from the mixtures, the elements which exist in the mixture are destroyed so that they can no longer exist in the hylomorphic compounds as themselves.