The purpose of this essay is to discuss the arguments that St. Thomas Aquinas presents for the existence of God. It will first list his five arguments briefly, then present a brief explanation of three of them. Of these, one will be chosen for discussion in depth. It will be evaluated and discussed in relation to Aristotelian theories and arguments and in relation to other Thomistic theories.
AquinasÆs five basic a posteriori arguments for the existence of God (as summarized in Summa Theologica, Part I, Question 2, Article 3) are as follows.
First is the argument from motion, which he attributes to Aristotle, according to which all motion must ultimately be caused by an unmoved mover.
Second is the argument from the nature of an efficient cause, that is, by progression from contingent beings, which cannot cause their own being, to the being which needs no cause because its essence is existence itself.
Third is the argument from possibility and necessity, that is, from beings whose existence is only possible but not necessary to the one being whose existence is necessary and for whom nonexistence is not possible.
The fourth is the argument from imperfection, that is, from the imperfection of material objects to the absolute perfection of the divine. This derives ultimately from PlatoÆs argument for the existence of perfect ideas in contrast to the imperfections of material objects.
The fifth is the argument from the ôgovernance of the worldö or from order, that is, from that fact that everything ôworks toward an end,ö toward the ultimate source of the order in the cosmos.
The argument from motion is the most detailed of the arguments that Aquinas presents, and is the one that will be analyzed in detail here. In brief, the concept is that everything that does not move itself, of which there are ample examples, must be moved by something else. Aristotle had argued that either there must be an infinite regr...