On The Holy Trinity by St. Augustine
Chapter 4.--The Same Argument Continued.
6. For in like manner the virtues which are in the human mind, although each has its own several and different meaning, yet are in no way mutually separable; so that, for instance, whosoever were equal in courage, are equal also in prudence, and temperance, and justice. For if you say that such and such men are equal in courage, but that one of them is greater in prudence, it follows that the courage of the other is less prudent, and so neither are they equal in courage, since the courage of the former is more prudent. And so you will find it to be the case with the other virtues, if you consider them one by one. For the question is not of the strength of the body, but of the courage of the mind. How much more therefore is this the case in that unchangeable and eternal substance, which is incomparably more simple than the human mind is? Since, in the human mind, to be is not the same as to be strong, or prudent, or just, or temperate; for a mind can exist, and yet have none of these virtues. But in God to be is the same as to be strong, or to be just, or to be wise, or whatever is said of that simple multiplicity, or multifold simplicity, whereby to signify His substance. Wherefore, whether we say God of God in such way that this name belongs to each, yet not so that both together are two Gods, but one God; for they are in such way united with each other, as according to the apostle's testimony may take place even in diverse and differing substances; for both the Lord alone is a Spirit, and the spirit of a man alone is assuredly a spirit; yet, if it cleave to the Lord, |it is one spirit:| how much more there, where there is an absolutely inseparable and eternal union, so that He may not seem absurdly to be called as it were the Son of both, when He is called the Son of God, if that which is called God is only said of both together. Or perhaps it is, that whatever is said of God so as to indicate His substance, is not said except of both together, nay of the Trinity itself together? Whether therefore it be this or that (which needs a closer inquiry), it is enough for the present to see from what has been said, that the Son is in no respect equal with the Father, if He is found to be unequal in anything which has to do with signifying His substance, as we have already shown. But the apostle has said that He is equal. Therefore the Son is equal with the Father in all things, and is of one and the same substance.