“The term homoousios (of one substance) may express a grasp of the true faith; but it lends itself to deception. If we apply it to a combination of distinction and likeness of nature, to insist that the ‘likeness’ asserts not a likeness in mere externals (speciem) but in underlying reality (genus), then our teaching accords with the truth of our religion: providing that we take ‘one substance’ as meaning a likeness of distinct entities, so that unity means not numerical singularity but equality…. If ‘Father and Son or one substance’ is taken as implying a single entity, though signified by two names, we may confess the Son in name, but we do not acknowledge him in thought, if by confessing ‘one substance’ we are asserting that one single being is himself both Father and Son. Again, there is a foothold for the error which supposes the Father to have divided himself, to have cut off a part of himself to be his Son…. There is also a third error, which takes ‘Father and Son of one substance’ to indicate a prior substance, which the two share equally. The orthodox will assert ‘one substance of Father and son’; but he must not start from that: nor must he hold this as the chief truth, as if there could be no true faith without it. HE will assert ‘one substance’ without danger, when he has first said, ‘The Father is ingenerate; the Son has his origin and existence from the Father; he is like the Father in goodness, honour, and nature.’ He us subject to his Father, as the origin of his being…. He does not come from nothing; he is generate. He is not unborn; but he shares in timelessness. he is not the Father, but the Son derived from him. He is not a portion, he is a whole: not the Creator himself, but his image; the image of God, born of God, from God: he is not a creature; he is God. But he is not another God in underlying substance, but one God through essence of undiffering substance. God is one, not in person, but in nature.”(De synodiis 67-69)
“I know, dearest brethren, that some acknowledge the likeness, while denying equality…. If they say that there is a difference between likeness and equality, I ask what is the basis of equality. For if the Son is like the Father in essence and goodness and glory and time, I ask in what way does he appear not to be equal…. If the Father has given to the son, whom he has generated impassibly, a nature that was not other than his own, nor different from his own, it must have been his own nature that he gave. Thus ‘like’ means ‘his own’; and that entails equality, the absence of difference. Things which show no difference are one; not by unity of person, but by equality of nature.”(De synodiis, 74)
First, it is necessary to note quite plainly that St. Hilary specifically objects to any ordo theologiae which would make the consubstantial divine essence itself the starting point for theology, i.e., which would place it first in the order of concepts to be explicated. This is crucial, for it is precisely this step which will emerge in the Augustinian exposition of Trinitarian doctrine. Second, in this regard it is to be recalled that St. Basil himself specifically warned against such an ordo. Thus, St. Hilary and the Cappadocians are not doing “Eastern” vs. “Western” theology, but Catholic, Apostolic, and Patristic theology. One and the same mind, or a common ordo theologiae is found in all. Thus, for St. Hilary, as for the Cappadocians and all the other fathers examined to this point, the starting point for Trinitarian theology is the Monarchy of the Father. This adherence to tradition is manifest in Hilary in other ways, most notably by what his remarks imply for the relationship between philosophy and theology.
Hence, to restate what St. Hilary has said about homoousios and homoiousios in a way which this relationship will be clearer, we derive the following: ‘homoousios’ is understood by the orthodox Niceans as meaning simply ‘equality in essence of two individual entities’, which is the meaning assigned by both St. Athanasius and St. Basil. Thus, used as a specifically defined theological symbol and not with its philosophical connotation, the term is acceptable. The problem which the “orthodox Semi-Arians” have with it is precisely because they understand the word in its philosophical sense, which was not intended by the First Ecumenical Council. In this sense, the term ‘homoousios’ may be broken down to mean “same(homo) entity(ousios), in which case the word would mean that the Father and the Son were the same entity, or person. The homoiousions thus objected to the term because they rightly concluded that it could be understood in a Sabellian sense. their error was only that they understood a theological symbol in a philosophical manner. Conversely, the initial rejection of homoiousios by the orthodox Niceans was likewise based upon reading what the orthodox “Semi-Arians” understood as a theological symbol in a philosophical sense. The so-called Semi-Arians meant by the term entities which were “like” each other, or the “same” in essence, but they chose the term to protect their unique Personhood. But, since the term ousios means not only “entity” but essence, confession of “likeness” seemed to the Orthodox Niceans as falling short of “identity”, and hence even an Arian could use the term(as they did, thus making it difficult to distinguish between the genuinely orthodox and the genuinely Arian factions within the “Semi-Arian” party). Thus, the orthodox Niceans committed the same mistake with their opponents, by understanding their term not as a theological symbol, but in a philosophical manner.
St. Hilary’s solution is therefore a brilliant though obvious one: the term homoousios is not a philosophical symbol, which insight, when coupled with the Cappadocians’ use of the equally strong hypostasis to designate the Three Persons, makes a reconciliation of the orthodox Semi-Arians to the Nicene formula possible.
Consequently, St. Hilary stands entirely outside any notion of a “Hellenization” of doctrine, and in fact, along with the Cappadocians, may be understood as the first father to reflect explicitly on the nature of theological language and vocabulary. For this reason, and for the fact that he disallows any beginning of theology at the consubstantial divine essence, he simply cannot be construed as a proto-Augustinian.
–excerpt from GHD