Chapter one serves as an introduction to the whole dissertation. In it I explain why I think philosophers should pursue a systematic, pluralist account of contemporary property roles and consider Thomistic explanations of such roles. I also summarize in more detail the chapters that make up this dissertation. In chapter two I explain the main metaphysical and semantic roles that properties are thought to play and briefly introduce the main contemporary accounts of properties in terms of which property roles they address and which they have trouble explaining.

In chapter three I consider one contemporary view of properties, namely robust Platonism regarding properties, which is explanatorily powerful but which has some objectionable features. I address one such feature that is of interest to theists. I show the failure of a recent attempt to reconcile robust Platonism regarding God's attributes with the classical theist views that God is ultimate in the explanation of all reality and that God does not depend on anything distinct from Himself for His existing or His intrinsic attributes. I argue further that there seems to be no other possible way to reconcile them. In chapter four, which is a brief interlude, I clarify some important differences between the account of the divine ideas on one type of theistic Platonism that I critique in chapter three and the accounts given by Augustine and by Aquinas.

In chapter five I disambiguate some of the various uses of property terms in contemporary Aquinas scholarship and resolve one substantive disagreement regarding what for Aquinas should be regarded as 'properties'. Then I critique and modify some features of Jeffrey Brower's reconstruction of Aquinas's account of the same-species relation and use the modifications in my own account, which yields a distinctive explanation of the metaphysical property role of accounting for the substantive similarities between things. In chapter six I lay some groundwork for a Thomistic account of the metaphysical property roles of accounting for the characteristics and metaphysical constitution of individual things. I do so by critiquing and modifying Brower's account of Aquinas's hylomorphism as a unique type of substratum theory.