ACT, PURE (Greek ενεγεια καθ’ αυτη [energeia kath’ auté]; Latin actus purus)—a description of the Absolute (God) in the philosophy of Aristotle and Thomas Aquinas.
Pure act is the fullness of actuality or being in various ways. It means simplicity in being, invariability, absence of limits, immateriality, singularity, the absence of a beginning and an end in being, the absence of succession, complete identity, Truth itself, the Good itself (Love), Beauty itself, and a Person.
Aristotle was the first to formulate a proof for the existence of the Absolute in the context of an analysis of motion, and he drew upon his theory of act and potency. Motion, or more specifically change, is an actualization of potency (the actualization may be instantaneous or in succession). A being that is composed of matter and form is found in an actual-potential state, i.e., in motion. The being’s structure and mode of existence manifest its non-necessity and its derivative nature. Everything that is such, that is, everything that changes, passes from potency to act because of an external agent of motion which is in act. The existence of potency without act is impossible. Every change therefore requires an actual moving cause. Since an infinite series of agents that cause motion is impossible, therefore a first mover exists, but that first mover is free of all potentiality—Pure Act as the absolute beginning of all motion. In Aristotle’s philosophy, the Absolute—Pure Act— is a pure form, the most perfect being who is necessary, unchanging, eternal, alive, who is intellect and the self-thinking thought.
Thomas Aquinas accepted Aristotle’s argument from the analysis of motion for the existence of the Absolute (God) as Pure Act and added his own refinements. This proof expressed in the first of Aquinas’ “five ways”, the so-called way of motion. Thomas modified the Aristotelian conception of being, and at the same time he went deeper into Aristotle’s theory of act and potency. A being is something that exists and is composed of essence and existence. Motion is the actualization of potency in a being. Thomas’ way of motion takes into account the actualization of a being’s existence by pure existence. The becoming of a being is an actualization of existence. To explain this, we must explain the existence of a being not composed of potency and act—a pure existence as Pure Act. Such an act is the cause of the actualization of the existence of all being. Being conceived in metaphysical terms, specifically being in motion, leads to the discovery of the existence of a being who is Pure Act. As a perfect being and the fullness of being, he is a Person who rationally and freely calls beings into existence (or actualizes them)
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