Before we conclude, we wish to make a few remarks on some ambiguous expressions which may be a source of error in speaking of substance and of suppositum. We have said that Aristotle includes in his first category the suppositum as well as the substance, and that for this reason the words, “by itself,” “to support,” “to subsist,” have been promiscuously applied to the substance as well as to the suppositum. This has been done not only in philosophy, but even in theology. Thus we read in good authors that the divine Person of the Word “supports” or “sustains” Christ’s human nature. Yet these words, as also “sustentation,” when applied to subsistence, must have a meaning which they have not when applied to substance; and it is plain that to employ the same words in both cases may give rise to serious mistakes. Some authors, besides overlooking the distinction to be made between “existing in itself”—_esse in se_—and “subsisting by itself”—_per se subsistere_—confound also with one another their opposites—viz., “to exist in something else”—_esse in alio_—and “to subsist by something else”—_per aliud subsistere_. Suarez, for instance, though usually very accurate in his expressions, says that “the mode of existing by itself and without dependence on any supporter has for its opposite to exist in something else;”(20) which is not correct, for the divinity of Christ exists in his humanity, and nevertheless does not depend on it as a supporter. It would be more correct to say that the mode of subsisting by itself has for its opposite to subsist by something else. And it is evident that to subsist _by_ something else is not the same as to exist _in_ it. To get rid of all such ambiguous phrases, we observe that the word “sustentation,” as compared with any created nature, can have three different meanings, according as we apply it to the act, the term, or the complement of the created being. When sustentation is considered in connection with the act or the formal principle of a being, it means positive _conservation_; for all contingent being comes out of nothing by the positive production of an act, and needs to be kept out of nothing by the positive conservation of the same act, as we know from special metaphysics. When sustentation is considered in connection with the intrinsic term of a being, it means _underlying_; and in this sense we say that substance sustains its accidents. This meaning of the word “sustentation” is most conformable to its etymology; and thus, if anything is lying under any reality in that manner in which substance lies under its accidents, we shall say very properly that it _sustains_ that reality. In this sense, sustentation and support may be taken as synonymous.