In the letter which I ventured to address to you a short time ago concerning the general conditions required in a good English work of philosophy, I made some observations on the importance and difficulty of wielding the popular language in a strictly philosophical manner. As I apprehend that the title of "Philosophical Terminology," under which that letter was made to appear, is scarcely justified by its very limited contents, I beg leave to add a few other considerations on the same subject, that your intelligent readers may find in these additional remarks a confirmation and a further development of what I said about our need of a more copious philosophical language.
There are two words which cannot easily be dispensed with in the metaphysical analysis of created beings; these two words are, in Latin, actus and potentia. Metaphysicians, in fact, conclusively prove that in every created substance there are two essential principles: a principle of activity, which is known under the name of actus, and a principle of passivity, which is styled potentia. These two terms, which are so necessary in metaphysics, and so familiar to all the scholastic philosophers, might be fairly represented in English by "act" and "potency"; though as yet neither "act" nor "potency" is popularly used in this philosophical sense.
The word "act" with us primarily signifies that which is produced by action; for all action is the production, or the position, or the making of an act. But all action implies an agent—that is, a being which is already "in act," with its actual power prepared for action. On the other hand, nothing is formally "in act," but through an intrinsic "act," which is the formal principle of its actuality. Accordingly, the word "act," though primarily known to us as expressing the product of action, must, by metaphysical necessity, be applied also to that from which every agent and every being has its actuality.
Hence, philosophers found it necessary to admit two kinds of "acts"—the essential and the accidental. The essential is that which gives the first actuality, or existence, to a being—dat esse simpliciter. The accidental is that which is received in a subject already existing, and which only gives it an accidental actuality or a mode of being—dat esse secundum quid.
But the essential act (which is also called substantial, though it has a more extensive meaning, as we shall see hereafter) is, moreover, to be distinguished from actual existence. Metaphysicians, indeed, very often speak of existence as an act; and hence, to avoid confusion and equivocation, they are obliged to distinguish the actus essentiæ from the actus existentiæ. Yet, to speak properly, existence is not simply an act; it is the actuality of the being;[68] and, consequently, the distinction which must be admitted between the essential act and the existence of a being is not strictly a distinction between two acts, but between the act which actuates the essential term of the being, and the actual state which results from such an actuation. I will say more on this point when I have explained the use of the word "potency."
The English word "potency" is the equivalent of the Latin potentia. This Latin word, although used most frequently in the sense of "passive principle," is not, however, necessarily connected with passivity more than with activity; and accordingly it has been used as well to designate "active power." Hence, it is obvious that this term, potentia, when employed absolutely without the epithet activa or passiva, is liable to two interpretations, and becomes a source of mischievous equivocations. I do not see what prevented our old Latin philosophers from designating the two kinds of potentia by two different words. Had they constantly used virtus or vis for the potentia activa, and reserved potentia exclusively for the potentia passiva, they would not have mistaken the one for the other, as they sometimes did. Let me quote a few examples of this for our common instruction.
Sanseverino, a very learned man, and one of the best modern scholastics, while arguing against the Scotists, who deny all real distinction between the soul and its faculties, says that if the soul and its faculties are really the same thing, then, "as the soul is always in act, the faculties also must be always in act and never in potency." Whence he infers that "the soul would have no potentiality, and would therefore be a purus actus like God"; which is, of course, a pantheistic absurdity.[69] But evidently this inference has no other foundation than the confusion of the potentia activa with the potentia passiva. The author, in fact, knows perfectly well that no being in which there is potentia passiva can be styled purus actus: when, therefore, he draws the conclusion that the soul, in the Scotistic theory, would be purus actus, he must be understood to mean or imply that all potentia passiva would be excluded from the soul. Yet his premises are concerned with the potentia activa only; and it is quite evident, that from such premises he could not have passed to such a conclusion had he not confounded the two kinds of potentia with one another.
I would remark, also, that in his argument the expression, "The faculties must be always in act," cannot mean that the faculties must be always acting, but only that they are always actual, as the soul itself; and, therefore, the author cannot reasonably conclude that the faculties "would never be in potency" respecting their proper acts. The potentia activa is already an "act," as it is known, since it is called actus primus agendi; and is not called potentia, except as contrasted with its accidental operations. Moreover, a faculty does not cease to be potentia activa, even when it actually performs its operations. When I actually make a syllogism, my faculty of reasoning is "in act," and yet it retains its potentia activa with regard to any number of other syllogisms. It is not true, therefore, that a faculty which is in actual operation ceases to be in potentia activa. Lastly, the soul itself, which, as Sanseverino remarks, is always in act, is nevertheless always in potency also; for the actuality of all contingent being is always potential—that is, liable to modifications of different kinds. Hence, we not only deny the conclusion of the learned author as illegitimate, but affirm that the premises themselves, on which he relies, are untenable. It is the indiscriminate use of the word potentia that vitiates the author's argumentation.
Another great Thomist, Goudin, wishing to prove that in all creatures the power of acting is an accident, argues that potentia et actus sunt idem, quamvis diversimode, and that actus est semper nobilior quam potentia ad eum essentialiter ordinata; whence he concludes that, if a given act is an accident, the active power, whence it proceeds, must needs be an accident too. Here, also, the equivocation is evident. The act is nobilior quam potentia when we compare it with the potentia passiva which is destined to receive it—that is, to be actuated by it—but when an act is compared with the active power from which it proceeds—that is, with the potentia activa—we cannot say that it is nobilior quam potentia ad eum essentialiter ordinata: it is the contrary that is true. Had the author used the word virtus agendi instead of the equivocal word potentia, he would soon have discovered the fallacy of his argument.
I am sorry to say that even S. Thomas sometimes forgets to observe the distinction between potentia activa and potentia passiva; as in the first part of his Summa, where he compares the potentia essendi and the potentia operandi with their respective acts, and establishes a kind of proportion between the two potencies and the two acts.[70] No such proportion can be admitted, unless the potentia operandi and the potentia essendi are both similarly connected with their acts. Yet whilst the potentia operandi is active, the potentia essendi, according to S. Thomas, is passive.[71] They cannot, therefore, be related to their acts in a similar manner. Hence, the terms are not homologous, and the proportion cannot subsist. In another place, the holy doctor argues that, if an act is accidental, the potentia from which it proceeds must be accidental also; because potentia et actus dividunt ens, et quodlibet genus entis, and, therefore, oportet quod ad idem genus referatur potentia et actus.[72] But the potentia which, with the actus, constitutes the being and every class of beings is the potentia passiva; whilst the potentia from which any act proceeds is the potentia activa. The argument, therefore, contains four terms, and proves one thing only, namely, that it is extremely difficult, even for the greatest men, to avoid equivocations when things that are different and opposite are designated by the same term.