In what does the causal influence of the formal cause consist? In communicating itself intrinsically to the material principle or passive subject from whose potentiality it is evoked by the action of efficient causes; in actuating that potentiality by intrinsic union therewith, and thus determining the individual subject to be actually or formally an individual of such or such a kind.
The material and formal causes are intrinsic principles of the constitution of things. We next pass to an analysis of the two extrinsic causes, and firstly of the efficient cause and its causality.
97. Efficient Cause; Traditional Concept Explained.—By efficient cause we understand that by which anything takes place, happens, occurs: id a quo aliquid fit. The world of our external and internal experience is the scene of incessant changes: men and things not only are, but are constantly becoming. Now every such change is originated by some active principle, and [pg 367] this we call the efficient cause of the change. Aristotle called it τὸ κινητικόν or ἡ ἀρχὴ κινητική, the kinetic or moving principle; or again, ἀρχὴ κινησέως ἢ μεταβολῆς ἐν ἑτέρω, principium motus vel mutationis in alio, “the principle of motion or change in some other thing”. The result achieved by this change, the actualized potentiality, is called the effect; the causality itself of the efficient cause is called action (ποίησις), motion, change—and, from the point of view of the effect, passio (παθήσις). The perfection or endowment whereby an efficient cause acts, i.e. its efficiency (ἐνέργεια), is called active power (potentia seu virtus activa); it is also called force or potential energy in reference to inanimate agents, faculty in reference to animate agents, especially men and animals. This active power of an efficient cause or agent is to be carefully distinguished from the passive potentiality acted upon and undergoing change. The former connotes a perfection, the latter an imperfection: unumquodque agit inquantum est in actu, patitur vero inquantum, est in potentia. The scope of the active power of a cause is the measure of its actuality, of its perfection in the scale of reality; while the extent of the passive potentiality of patiens is a measure of its relative imperfection. The actuation of the former is actio, that of the latter passio. The point of ontological connexion of the two potentiae is the change (motus, κίνησις), this being at once the formal perfecting of the passive potentiality in the patiens or effect, and the immediate term of the efficiency or active power of the agens or cause. Actio and passio, therefore, are not expressions of one and the same concept; they express two distinct concepts of one and the same reality, viz. the change: actio et passio sunt idem numero motus. This change takes place formally in the subject upon which the efficient cause acts, for it is an actuation of the potentiality of the former under the influence of the latter: ἡ κίνησις ἐν τῷ κινητῷ; ἐντελέχεια γὰρ ἐστι τόυτου. Considered in the potentiality of this subject—“τὸ τοῦδέ ἐν τῷδε: hujus in hococ”—it is called passio. Considered as a term of the active power of the cause—“τοῦδε ὑπο τοῦδε: hujus per hoc”—it is called actio.
The fact that actio and passio are really and objectively one and the same motus does not militate against their being regarded as two separate supreme categories, for they are objects of distinct concepts,[450] and this is sufficient to constitute them distinct categories ([60]).
Doubts are sometimes raised, as St. Thomas remarks,[451] about the assertion that the action of an agent is not formally in the latter but in the patiens: actio fit in passo. It is clear, however, he continues, that the action is formally in the patiens for it is the actuation not of any potentiality of the agent, but of the passive potentiality of the patiens: it is in the latter that the motus or change, which is both actio and passio, takes place, dependently of course on the influence of the agent, or efficient cause of the change. The active power of an efficient cause is an index of the latter's actuality; the exercise of this power (i.e. action) does not formally perfect the agent, for it is not an actuation of any passive potentiality of the latter; it formally perfects the patiens. Only immanent action perfects the agent, and then not as agent but as patiens or receiver of the actuality effected by the action (cf. [103] infra).
We may, then, define efficient cause as the extrinsic principle of the change or production of anything by means of action: principium extrinsicum a quo fluit motus vel productio rei mediante actione.
It is a “first” principle as compared with material and formal causes for its influence is obviously prior in nature to theirs; also as compared with the other extrinsic cause, the final cause, in ordine executionis, not, however, in ordine intentionis. The “end,” not as realized but as realizable, not in execution but in intention, discharges its function and exerts its influence as “final cause” and in this order the final cause, as will appear later, is the first of all causes: finis est ultimus in executione sed primus in intentione.
“Change or production,” in the definition, is to be understood not in the strict sense in which it presupposes an existing [pg 369] subject or material, but in the wide sense in which it includes any production of new reality, even creation or production ex nihilo.
“Action,” too, is to be understood in the wide sense in which it includes the action of the First Cause, which action is really identical with the essence of the latter. We conceive creation after the analogy of the efficient action of created or “second” causes: we have no proper concept of the infinite perfection of the Divine activity. In all created efficient causes not only is the action itself, but also the efficiency, force, power, faculty, which is its proximate principle, really distinct from the nature or essence of the agent; the former is a substance, the latter an accident.
Finally, the action of a created efficient cause is either transitive (transiens) or immanent (immanens) according as the change wrought by the action takes place in something else (as when the sun heats or lights the earth) or in the cause itself (as when a man reasons or wills). In the former case the action perfects not the agent but the other thing, the patiens; in the latter case it perfects the agent itself, agens and patiens being here the same identical concrete individual.[452]