In English, the word potentia is commonly represented by "power," to which the epithets of "active" and "passive" have been attached by some writers, in the same manner as was done with the Latin potentia. "Power," says Locke,[73] "may be considered twofold, namely, as able to make or able to receive any change." But "in strictness," says Webster, "passive power is an absurdity in terms. To say that gold has a power to be melted is improper language; yet for want of a more appropriate word, power is often used in a passive sense."
It is not true, however, that "the want of a more appropriate word" really compels us to use the word power in a passive sense. Have we not the word potency? This word exactly answers our purpose. It is not only the exact equivalent of the Latin potentia, but is also the immediate relation of the terms potential, potentially, potentiality, which are already admitted in common philosophical language as expressing capability, passiveness, and liability. These latter words are only subordinate members of a family, of which potency is the head. Therefore, to convey the notion of potentia passiva, we have a more appropriate word than "power," and nothing compels us to employ the absurd expression of "passive power." On the other hand, the remarks above made, on the consequences of the promiscuous use of the word potentia in the active and the passive sense, would suffice to show that the word "power," even if it could be used without absurdity in the passive sense, should, in philosophy, be restricted to the active; as it is most desirable that things which are so thoroughly opposite be expressed by different words. Thus, the word "power" retaining its active meaning, the potentia passiva may very appropriately be styled "potency."
Some will ask, Why should we use the word "potency" in this new sense, while we have already the term "potentiality," which seems to express very exactly the same notion? I answer that the principle of passivity, which we call "potency," is an essential constituent of created beings; whilst "potentiality" is not an essential constituent, but an attribute flowing from the essential constitution of being, on account of the potency which the latter involves. Accordingly, "potentiality" cannot stand for "potency," any more than rationality can stand for reason, or materiality for matter.
From the foregoing considerations, it appears that the words "act" and "potency" cannot be easily dispensed with in metaphysics, and, therefore, should be freely admitted and acknowledged as philosophical terms. As to their definitions, however, we shall have to rely on philosophical treatises rather than on common English dictionaries. The word "act" is indeed to be found in all dictionaries; but, unfortunately, its meaning is restricted to the expression of mere accidents, while substantial acts are ignored altogether. In Fleming's Vocabulary of Philosophy we find: "Act in metaphysics and in logic is opposed to power. Power is simply a faculty or property of anything, as gravity of bodies. Act is the exercise or manifestation of a power or property, the realization of a fact, as the falling of a heavy body." On these words I would incidentally remark that "power" cannot be defined a "faculty"; because, though all faculties are powers, yet there are powers which are not faculties. Again, "power" cannot be defined a "property" without adding some restriction; as there are properties which are not powers. Moreover, the "gravity of bodies" is not a power, as some unphilosophical scientists imagine, but is a simple tendency to fall, owing to the fact that the active power of the earth is actually applied to the passive potency of the body. Nor is it true that in metaphysics or in logic the act is the "exercise or manifestation of a power." Such an exercise and manifestation is action—that is, the position or the production of the act. As to "the falling of a heavy body," it is true that we usually call it an act, but we evidently mean actuality; for, if the falling were an act strictly, then the tendency to fall would be an active power; which it is not. Lastly, the most important metaphysical meaning of the word "act," and of its correlative, "potency," is not given; which, however, is not owing to any oversight of the author, as we have already said that these two words were not used by English writers in this philosophical sense.
In Worcester's and Webster's dictionaries, the word act is said to mean action, exertion of power, and real existence as opposed to possibility. From the preceding remarks, it may be seen that, in metaphysics, none of these three meanings can be considered rigorously accurate.
Act, in the scholastic language, is that which gives existence by formal actuation. Potency is that which, by formal actuation, receives existence. Actuality is the result of the actuation—that is, the very existence of the act in its potency. Actuality, as we have already remarked, was also called actus existentiæ; hence, existence itself was considered as an act received in the essence, and causing it to be. But this view is now generally abandoned, because it has been shown that it is not the existence that entails the reality of the act and the potency, but the real position of the act in its potency that entails the existence of the being. Accordingly, existence is not an act received in the essence, but the result of the position of the essence; and cannot be called an act, except in a logical sense, inasmuch as it gives to the being denominationem existentis.
An act is called essential when it gives the first existence to any essence, be it simple or compound; substantial, when it gives the first existence to a pure potency; accidental, when it gives a mode of being. The distinction between essential and substantial acts will be explained here below, where we examine the different kinds of forms.
Every being acts inasmuch as it is in act, and is acted on inasmuch as it is in potency. Hence, the substantial act is a principle of activity, and the potency a principle of passivity.
The active power of any being, if taken in the concrete, is nothing but its substantial act as ready for exertion, and is called active power, because its exertion is the position or the production of an act. The active power thus considered is, therefore, in reality one of the constituent principles of natural beings; whilst the abstract term activity does not stand for a principle, but for an attribute of the being—that is, for its readiness to act.
The passive potency of any being, if taken in the concrete, is nothing but the term of the substantial act as liable to be acted on, and is called passive or receptive, because it is actuated by the reception of an act. The passive potency, thus considered, is therefore in reality one of the constituent principles of natural beings, whilst the abstract term passivity does not stand for a principle, but for an attribute of the being—that is, for its liability to be acted on.