This is all true; it is as strong arguing from effect to cause, as it is from cause to effect. But do the arguments prove the same thing? Let us see. I know a thing to exist; and therefore it does exist. This is to reason from effect to cause. The conclusion is inevitable; but what does it prove? Why, it proves that the thing does exist--it proves the bare fact of existence. The indissoluble connexion, or the necessity, in this case, exists between the knowledge and the event known; and it has no relation to the question how the event came to exist. This argument, then, in regard to human volitions, only proves that they are indissolubly connected with their effects, and are necessarily implied by them; just as every cause is implied by its effects: but no libertarian in the world has ever questioned such a position. For all that such an argument proves, all the volitions of moral agents may come into existence, without having the least shadow of reason or ground of their existence. We admit that volitions are efficient causes; and that they have effects, with which they are indissolubly connected. Edwards undertook to show, that volitions are necessary, because they are infallibly and indissolubly connected with their causes; and he has shown that they are necessary, because they are infallibly and indissolubly connected with their effects! This is one branch of his great argument. There is another sense, in which the knowledge of an event, whether it be _fore_, or _after_, or _concomitant_, knowledge, proves it to be necessary. This sense is not clearly distinguished from the former by Edwards. He recognizes them both, however, although he blends them together, and frequently turns from the one to the other in the course of his argument. It is highly important, and affords no little satisfaction, to keep them clearly distinct in our minds. A thing is said to be necessary, as we have seen, because it is connected with the knowledge of it; and, if a thing does exist, or is certainly and infallibly known to exist, it may be said to be necessary, on the principle that it is impossible it should exist and not exist at one and the same time. These two things are evidently different; and, for the sake of distinctness in our language, as well as in our thoughts, I shall call the first a _logical_, and the last an _axiomatical_ necessity. A thing, then, which does exist, is said to be necessary with an _axiomatical_ necessity; because it is impossible for it not to exist while it does exist: and it is said to be necessary, with a _logical_ necessity, because it is indissolubly connected with the knowledge of it. The former kind of necessity is frequently presented in this form of expression, that if a thing does exist, it is impossible it should be otherwise than true that it does exist. In this form of expression, it is frequently resorted to by Edwards.