Let it then be understood that God and nature make nothing to be idle. Whatever comes into being, exists for some operation or working. For no created essence is an ultimate end in the creator's purpose, so far as he is a creator, but rather the proper operation of that essence. Therefore it follows that the operation does not exist for the sake of the essence, but the essence for the sake of the operation. There is therefore a certain proper operation of the whole body of human kind, for which this whole body of men in all its multitudes is ordered and constituted, but to which no one man, nor single family, nor single neighbourhood, nor single city, nor particular kingdom can attain. What this is will be manifest, if we can find what is the final and characteristic capacity of humanity as a whole. I say then that no quality which is shared by different species of things is the distinguishing capacity of any one of them. For were it so, since this capacity is that which makes each species what it is, it would follow that one essence would be specifically distributed to many species, which is impossible. Therefore the ultimate quality of men is not existence, taken simply; for the elements share therein. Nor is it existence under certain conditions;[154] for we find this in minerals too. Nor is it existence with life; for plants too have life. Nor is it percipient existence; for brutes share in this power. It is to be percipient[155] with the possibility of understanding, for this quality falls to the lot of none but man, either above or below him. For though there are other beings which with him have understanding, yet this understanding is not, as man's, capable of development. For such beings are only certain intellectual natures, and not anything besides, and their being is nothing other than to understand; which is without interruption, otherwise they would not be eternal. It is plain, therefore, that the distinguishing quality of humanity is the faculty or the power of understanding. [Footnote 154: "_Esse complexionatum._"] [Footnote 155: "_Apprehensivum per intellectum possibilem._" _V. Aquin._ I. 79, 1, 2, 10.]