An act or being which does not last, not even one instant, is nothing; because our mind cannot conceive a being to exist, and have no duration whatever. Therefore an act or being necessarily implies duration, and they are therefore one and the same thing.
But it will be remarked: Are there no transitory acts? Do not all philosophers admit the existence of acts which are continually changing?
We answer, What is meant by a transitory act? Does it mean something which is continually changing, so much so that none of its elements has any duration whatever, not even for an instant; or does it mean that the parts or moments, if we may call them so, are in a state of continual transition? In both cases such acts do not and cannot exist.
Before demonstrating this, we observe that it was the ancient Italian school of Elea which, before every other school, raised the problem of transient acts, pointed out the great difficulty which existed in explaining their nature, and demonstrated the impossibility of their existence. To render the demonstration clear, we remark that a transient act may mean either one of two things: an act which is composed of different parts, each in continual transition; or an act which has a beginning, and, after a certain duration, also an end. We admit the existence of such acts in the second sense and not in the first. For if an act continually changes, none of the states which it successively assumes have any duration whatever. Otherwise it would no longer be a transient act in the first sense. But that which has no duration at all cannot be considered to exist. Therefore an act really transient cannot exist. What then is a transient act? We have seen that it supposes something standing or lasting. But what lasts is immanent, that is, has duration. Therefore a transient act can only be the beginning or end of an immanent act, or, in other words, the beginning or end of duration. To illustrate this doctrine by an example: suppose I wish to draw a line on this paper. If all the points, of which the line is to be composed, were to disappear the very instant I am drawing them, it is evident I should never have a line. Likewise, if all the states, which a transient act assumes, are supposed to have no duration whatever, the act also can have no duration, and hence no existence. A transient act, then, is the beginning or end of an immanent act.
Having laid down the foregoing propositions, we come to the discussion of the pantheistic idea of the infinite.
What, according to pantheism, is the idea of the infinite? Something the essence of which consists in becoming, in being made, in fieri. Now, we reason thus: a being the essence of which lies in becoming means either an act permanent and lasting, capable of changes, or it means something the essential elements of which are continually changing, and have, therefore, no duration whatever. If the last supposition be accepted as describing the pantheistic idea of the infinite, then the infinite is a sheer absurdity, an absolute nonentity. For, in this case, the infinite would be a transient act, in the sense that its essential elements are continually changing, and have no duration whatever. Now such acts are absolutely inconceivable. The mind may put forth its utmost efforts to form an idea of them, yet it will ever be utterly at a loss to conceive anything about them.
Pantheism, on this supposition, would start from absolute nihilism, to build up the existence of everything. On the other hand, if the second supposition be admitted, that the infinite is a permanent being, capable of changes and developments, then it is a transient act in the second sense, that is, the beginning or end of an immanent act; in which case we object to its being self-existing, and insist that it leads to the admission of the idea of the infinite as given by the Catholic Church. We demonstrate this from the ontological idea of immanent and transient acts.
If there be transient acts, there must also be immanent acts, because transient acts are the beginning or end of immanent acts. But no immanent act can be the cause of its end, because no act could be the cause of its cessation; nor can an immanent act be the cause of its own beginning, since in that case it would act before it existed.