Pure act is an expression used in scholastic philosophy and theology to describe the absolute or pure perfection of God, in contrast with the limited or mixed perfection of creatures. act here is a technical term meaning actually possessed perfection, while pure means unmixed with potency, that is, with any intrinsic capacity for change or limitation. The expression is to be understood, therefore, in function of the general theory of potency and act initiated by aristotle and further developed by St. thomas aquinas and scholastic thinkers from the 13th century on (see potency and act).
This theory was originally developed by Aristotle to explain change or motion. Potency was conceived as a capacity for change, and not yet as a principle of limitation. Hence, for Aristotle, any being that has no intrinsic potency for change but always actually possesses the full measure of perfection proper to it is a pure act. Since matter is of its nature a principle of change, a pure act must be a purely spiritual intelligence whose act or perfection consists in eternal, changeless, and blissful self-contemplation.
Although Aristotle's proof for the existence of an unmoved mover in the Physica (258b 10–267b 27) mentions only one such being explicitly, he seems finally to have admitted, for reasons based on the current astronomy, some 55 of these, each a prime mover for one of the heavenly spheres (Meta. 1073a 13–1074b 14). Perfection for him, as for pre-Christian Greek philosophy in general, seemed not to imply infinity, but rather connoted the formless, the indeterminate, and the imperfect. Thus pure act excluded change but not limitation, and there could be several different pure acts, each complete in its own act of self-contemplation.
When 13th-century Christian thinkers took over Aristotelian philosophy as an instrument of theology, they modified the Aristotelian notion of pure act and applied it to the Christian God, unique Creator of all. It then became the infinite plenitude of all possible perfection, from which all other beings received perfection in different limited degrees, each in proportion to the limiting potency or capacity of its own nature. Potency thus became a principle of limitation as well as of change, and all beings outside of God were seen to be, in some way, mixtures of act and potency. For St. Thomas, since the ultimate perfection of all things is existence itself, God is a pure subsistent act of existence, Ipsum Esse Subsistens, including all other perfections. At the opposite end of the scale of perfection lies pure potency or primary matter; considered in itself (though according to St. Thomas it could never exist by itself), this is pure capacity for perfection, with no act or perfection of its own (see matter and form).
The few modern philosophers outside the Aristotelian-scholastic tradition who have adopted the expression use it to convey a conception of God as Absolute Spirit, thinking Himself and the world in a single pure act of thought; this group includes G. W. F. hegel, G. gentile,M. blondel, and L. lavelle.
See Also: aseity (aseitas); god in philosophy, 3; infinity of god.
Bibliography: thomas aquinas, C. gent. 1.16–18, 28, 43; thomas aquinas, Summa theologiae, 1a, 3–4, 7. w. n. clarke, "Limitation of Act by Potency: Aristotelianism or Neoplatonism," The New Scholasticism 26 (1952) 167–194.
[w. n. clarke]