[140] The same thing cannot at the same time be and not be.
[141] There is no effect without a cause.
[142] Things which are equal to a third thing are equal to each other.
[143] The principle whence anything is, and the principle whence anything is made.
[144] Philosophers teach that one thing can precede another in three ways, to wit, by priority of time, by priority of nature, and by priority of reason. A thing existing while another thing is not yet in existence has, with regard to this latter, a priority of time. A thing, on the existence of which the existence of another depends, has, with regard to this latter, a priority of nature. A thing, the conception of which is needed to form the conception of another, has, with regard to this latter, a priority of reason. The priority of origin, by which one of the divine Persons is prior to another, is a priority of reason, not of nature, and implies no real dependence of one Person from another.
[145] See Liberatore, Metaph. Gen., n. 125.
[146] We advisedly employ the preposition from. There is a vast difference between depending on and depending from. To depend from is properly to be hanging from, as a lamp from the ceiling; but nothing forbids the use of the phrase in a metaphorical sense in order to translate the Latin phrase, pendere ab, for which we have no other equivalent. The usual English phrase, to depend on, corresponds to the Latin pendere ex. Were we to employ it also for pendere ab, a confusion would arise of the two different meanings. Certainly, the two phrases, Homo pendet a Deo, and Exitus pendet ex adjunctis express different kinds of dependence; and we cannot translate them into English in the same manner without setting their differences at naught. We would, therefore, say, that Man depends from God, and that Success depends on circumstances. In philosophy, both prepositions are needed, and, if used with proper discrimination, they will save us the trouble of many useless disputes.
[147] A being and its constituent principles may be said to have a certain dependence on one another, inasmuch as they have such an essential connection with one another that the one cannot be conceived apart from the other. But this so-called "dependence" means only correlation and "mutual exigency"; and therefore does not entail a priority of nature of the one with respect to the other. In a being, which is strictly one in its entity, there are three principles: an act, its term, and the actuality of the one in the other. The act has only a priority of origin with respect to its essential term, and both have only a priority of origin with regard to their formal actuality. They depend on one another in the sense explained, but not from one another. We shall treat of them in a future article.
[148] Toties autem causæ quoque dicuntur (qucties principia); omnes namque causæ principia sunt.—Aristotle, Metaph. 5.
[149] Priority of nature implies in that which is prior an existence independent of that which is posterior; but a mere formal act has no existence independent of the being of which it is a constituent; therefore, the formal act is not prior, by priority of nature, to such a being.