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.