On The Holy Trinity by St. Augustine
Chapter 2.--The Father and the Son are Together One Wisdom, as One Essence, Although Not Together One Word.
3. Therefore the Father and the Son together are one essence, and one greatness, and one truth, and one wisdom. But the Father and Son both together are not one Word, because both together are not one Son. For as the Son is referred to the Father, and is not so called in respect to Himself, so also the Word is referred to him whose Word it is, when it is called the Word. Since He is the Son in that He is the Word, and He is the Word in that He is the Son. Inasmuch, therefore, as the Father and the Son together are certainly not one Son, it follows that the Father and the Son together are not the one Word of both. And therefore He is not the Word in that He is wisdom; since He is not called the Word in respect to Himself, but only relatively to Him whose Word He is, as He is called the Son in relation to the Father; but He is wisdom by that whereby He is essence. And therefore, because one essence, one wisdom. But since the Word is also wisdom, yet is not thereby the Word because He is wisdom for He is understood to be the Word relatively, but wisdom essentially: let us understand, that when He is called the Word, it is meant, wisdom that is born, so as to be both the Son and the Image; and that when these two words are used, namely wisdom (is) born, in one of the two, namely born, both Word, and Image, and Son, are understood, and in all these names essence is not expressed, since they are spoken relatively; but in the other word, namely wisdom, since it is spoken also in respect to substance, for wisdom is wise in itself, essence also is expressed, and that being of His which is to be wise. Whence the Father and Son together are one wisdom, because one essence, and singly wisdom of wisdom, as essence of essence. And hence they are not therefore not one essence, because the Father is not the Son, and the Son is not the Father, or because the Father is un-begotten, but the Son is begotten: since by these names only their relative attributes are expressed. But both together are one wisdom and one essence; in which to be, is the same as to be wise. And both together are not the Word or the Son, since to be is not the same as to be the Word or the Son, as we have already sufficiently shown that these terms are spoken relatively.