Thomas Aquinas On The Principle Omne Agens Agit Sibi Simile

This dissertation is a comprehensive study of the principle omne agens agit sibi simile in Aquinas's writings. This axiom, which appears over 220 times in the Thomistic corpus, is sometimes referred to as the principle of similarity or similitude, since it states that every agent produces something like itself. Chapter One begins with a consideration of previous studies that have discussed the principle of similitude in Aquinas's writings. This chapter also includes a discussion of the dissertation's methodology, which explains how search parameters were formulated for the Index Thomisticus--an online searchable database of Aquinas's writings--to locate every instance of the principle of similitude in the Thomistic corpus. From the results of these searches, three philosophical contexts in which Aquinas employs the principle come to light: natural theology, natural philosophy, and philosophy of knowledge. The middle chapters of the dissertation study in detail Aquinas's uses of the principle in each of these three areas of his thought. Chapter Two examines his uses of the principle in natural theology, where he applies the principle to God's creative agency and employs the principle to justify ascribing analogical names to God. Chapter Three, which concerns Aquinas's application of the principle to the beings studied in natural philosophy, highlights Aquinas's view that a lower agent imitates God's efficient causality by producing something like itself. Chapter Four examines Aquinas's uses of the principle in philosophy of knowledge, where he applies the principle to the various types of agencies involved in the achievement of intellectual knowledge. Chapter Five considers the justification that Aquinas offers for the principle of similitude. In this discussion, it is shown that Aquinas's justification of the principle is connected to a hierarchy of various types of agents, each of which produces something like itself in some way. The conclusion states that the principle of similitude is a fundamental element of Aquinas's metaphysical thought, since he uses it to express the dynamism of being. Two appendices provide a catalog of Aquinas's uses of the principle of similitude, organized both chronologically and topically.