and in potentiâ with regard to the same determination.
Aristotle and St. Thomas explain this theory by many illustrations, one of which will suffice. The statue exists potentially in the block of marble, because marble has an aptitude to receive the shape of a statue. This aptitude is something real in the marble, since many other substances are deprived of it. It is a receptive potentiality. With regard to the same statue, the sculptor has the power, by his action, to carve the marble into the form of a statue. His is an active power, a real skill or ability which is lacking in many other persons. In order to have the actual statue (actus), it is necessary for the sculptor to exercise (actus) his real skill (potentia) on a substance which is not yet a statue, but which has a real aptitude (potentia) to become one. I can form no idea either of the marble's potentiality or of the sculptor's skill unless I first know what is meant by an actual statue. In the same manner, the man born blind is unable to understand what is meant by the faculty of vision. In general, potentia has no meaning, and cannot be defined except through the corresponding actus.
II.—The distinction between potentia and actus is at the basis of, and pervades, the whole scholastic system of philosophy and theology. Whatever is determinable is considered as potential with regard to the actual determination. Genus and species, subject and predicate, quantity and shape, child and adult, matter and form of the sacraments, etc., are examples of potentiality and actuality. Here we must confine ourselves to the fundamental applications in metaphysics and in psychology. (1) In metaphysics the distinction runs through the ten Aristotelian categories. All being, whether substance or accident, (q.v.) is either in actu or in potentiâ. The essence of creatures is a potentiality with regard to their existence. Material substances are composed of primary matter and substantial form (see Matter and Form), matter being a pure potentiality, i.e., wholly undetermined, and form being the first determination given to matter. Efficient causality is also an application of potentiality and actuality; the cause, when at rest, remains able to act. Change is a transition from the state of potentiality to that of actuality. Generation, growth, and evolution suppose a capacity which becomes fulfilled. (2) In psychology special emphasis is laid on the reality of the potentiæ, or faculties (q.v.), and their distinction both from the soul and from their operations. External senses are determined or actualized by an external stimulus (see Species), which gives them the determination necessary to the act of perception. The internal senses (sensus communis, phantasia, memoria, aestimativa) depend on external sensations for their exercise. Memory and imagination preserve in potentiâ traces of past impressions, and when the proper conditions are verified the image becomes actual. We have no innate ideas, but in the beginning human intelligence is simply a power to acquire ideas. By its operation, the active power of the intellect (intellectus agens) forms the species intelligibilis or the determination necessary to the intelligence (intellectus possibilis) for its cognitive act. All tendency and desire is actualized by some good which one strives to acquire. In rational psychology man is conceived as one substantial being, composed of body and soul, or matter and form, united as potentia and actus.
There is a tendency today in nearly all the sciences towards "actuality" theories. But, if analyzed carefully, such theories will necessarily yield potential elements. In all things we find capacities for further development and evolution, forces and aptitudes which come to be utilized little by little. In scholastic terminology these are now real, but not actual. They exist only as potentiæ, which, to manifest themselves, await the proper actualization.
Aristotle, passim. esp. Metaphysics, VIII (Berlin ed., 1831); St. Thomas, Comment in lib. IX Metaphys. (VIII of Berlin ed.) and passim in Summa Theologica and other works; Farges, Acte et puissance (3d ed., Paris, 1893), Matiére et forme (3d ed., Paris, 1894); Harper, The Metaphysics of the School, II, ii, iii, and V. ii, iii, passim (London, 1879); Baudin, L'acte et la puissance dans Aristote in Revue thomisii, VII (1899), 40, 153, 274, 584, VIII (1900), 273; Watson The Metaphysic of Aristotle, III, IV; Potential and Actual Reality in Philosophical Review, VII (1898), 337; Logan, The Aristotelian Concept of φύσις, in Philosophical Review, VI (1897), 18; de Vorges, L'acte et la puissance, in Annales de philosophie chrétienne, n. s., XIV (1886), 471; Boutroux in La grande encyclopédie, art. Aristote, § viii, Métaphysique; Baldwin, Dict. of Philos. and Psychol., s.v. Potentiality and Potency.
Actus primus, a technical expression used in scholastic philosophy. Actus means determination, complement, perfection. In every being there are many actualities, and these are subordinated. Thus existence supposes essence; power supposes existence; action supposes faculty. The first actuality (actus primus) begins a series; it supposes no other actuality preceding it in the same series, but calls for a further complement, namely, the second actuality (actus secundus). But as the same reality may be called "actuality" when viewed in the light of what precedes, and "potentiality" when viewed in the light of what follows (see Actus et Potentia), the meaning of the term "first actuality" may vary according to the view one takes, and the point where the series is made to begin. Primary matter (see Matter and Form) is a pure potentiality, and the substantial form is its first determination, its first actuality. The complete substance constituted by these two principles receives further determinations, which are, in that respect, second actualities. Yet these may also be conceived as first actualities. Thus the extensive quantity of a substance is a first actuality when compared to the shape. Power is a first actuality when compared to action. And this is the most frequent application of the terms actus primus and actus secundus. The former is the faculty; the latter, the exercise, or function. To see in actu primo simply means to have the sense of vision; to see in actu secundo is to actually perform acts of vision. The modern distinction of potential and kinetic energy might serve as another illustration: the loaded gun, or the engine with steam up represent first actualities; the bullet speeding to the mark, the engine flying over the rails, represent second actualities.
Actus Purus, a term employed in scholastic philosophy to express the absolute perfection of God. In all finite beings we find actuality and potentiality, perfection and imperfection. Primary matter, which is the basis of material substance, is a pure potentiality. Moreover, change necessarily supposes a potential element, for it is a transition from a state .of potentiality to a state of actuality; and material things undergo manifold changes in substance, quantity, quality, place, activity, etc. Angels, since they are pure spirits, are subject to none of the changes that depend on the material principle. Nevertheless, there is in them imperfection and potentiality. Their existence is contingent. Their actions are successive, and are distinct from the faculty of acting. The fact that all things have in themselves some potentiality warrants the conclusion that there must exist a being, God, from whom potentiality is wholly excluded, and who, therefore, is simply actuality and perfection, Actus Purus.
It is true that in the same being the state of potentiality precedes that of actuality; before being realized, a perfection must be capable of realization. But, absolutely speaking, actuality precedes poten-
