We all know the classical formulae—”three persons, one substance”; “one being in three hypostases”—and perhaps we even know that St Basil of Caesarea was partly responsible for securing this conceptuality in the Eastern tradition. But while everyone involved in the fourth century trinitarian debates agreed on the use of ousia to speak of the unity of the one God, it took sixty-plus years after the Council of Nicaea for the Church to achieve consensus on the use of hypostasis to specify the three individualities of the Godhead. St Basil’s development on this matter is particularly illuminating.
In common fourth century usage ousia and hypostasis appear to have functioned as synonyms, both inside and outside the Church. They were particularly used in the philosophical tradition to signify that which is. G. L. Prestige summarizes:
To sum up briefly the relations for hypostasis and ousia, it may be said first that they are often, for practical purposes, equivalent. Nevertheless, they are probably never strictly identical in meaning, except in the Western instances quoted above, in which hypostasis may be regarded as a literal representation of the Latin substantia. Both hypostasis and ousia describe positive, substantial existence, that which is, that which subsists. … But ousia tends to regard internal characteristics and relations, or metaphysical reality; while hypostasis regularly emphasises the externally concrete character of the substance, or empirical objectivity. Hence, with regard to the Trinity, it never sounded unnatural to assert three hypostaseis, but it was always unnatural to proclaim three ousiai; although some writers … occasionally use ousia in a sense approximating to that of hypostasis, definite examples of the reverse process are not often to be found. (God in Patristic Thought, p. 188)
While often employed synonymously, in other words, an important nuance of difference did exist between the two terms and was sometimes exploited by philosophers: ousia tended to signify the “what” something is, i.e., the common nature shared by individual things; hypostasis tended to signify things in their concrete, distinguishable existence. It is this nuance that was invoked in what became the classical trinitarian formulations.
In his Contra Eunomium Basil still uses ousia and hypostasis as synonyms. Hypostasis has not yet become a technical term for the Three of the Godhead:
Though Basil does not use hypostasis in Against Eunomius as a technical term for Father, Son, and Holy Spirit as he later does, his use of it in Against Eunomius provides the context for that later usage. Three features of Basil’s use of hypostasis stand out: (1) hypostasis is, for Basil, largely synonymous with ousia; (2) hypostasis has concrete connotations, and it gives ousia these same connotations when the words are used together; and (3) hints of Basil’s later Trinitarian use of hypostasis (as distinguished from ousia) emerge especially in those few passages where hypostasis is used without any allusion to ousia. (Stephen Hildebrand, The Trinitarian Theology of Basil of Caesarea, p. 58)
An important, and unique, example:
So, then, if holiness is the Spirit’s nature, as it is for the Father and the Son, how does he have a nature that is third and foreign to theirs? I think that Isaiah recorded the Seraphim crying out “holy!” three times for this reason: because holiness in nature is observed in three subsistences [hypostaseis]. (Eun. 3.3)
This is the only occasion in Contra Eunomium where Basil speaks of the Father, Son, and Holy Spirit as three hypostases.
How then does the Bishop of Caesarea distinguish the Three in Contra Eunomium without compromising the divine unity and simplicity? He does so through the development of the idiomata (often translated “distinguishing marks,” “properties,” “particularities,” “particular qualities,” etc.). Basil’s presentation can be confusing, because he also uses the same family of terms to speak of the the propria that belong to and reveal the divine substance. The difference is that the propria are predicated of the common ousia, whereas the distinguishing terms refer to that which is unique to Father, Son, Spirit.
In his Apology Eunomius argues that the Son possesses a different substance from God because, unlike God, he is called “begotten,” “offspring,” “thing made”–different names demonstrate differences in substance (Apol. 12). Basil responds to this argument by comparing the terms “Father”/”unbegotten” and “Son”/”begotten” to proper names. Consider two individuals, Peter and Paul. Both share the same substance, i.e., both are human beings, yet they differ from each other by their idiomata:
In most respects we are the same as one another, but it is only due to the distinguishing marks considered in connection with each one of us that we are different, each from the other. Hence the designations do not signify the substances, but rather the distinctive features that characterize the individual. So whenever we hear ‘Peter,’ the name does not cause us to think of his substance—now by ‘substance’ I mean the material substrate which the name itself cannot ever signify—but rather the notion of the distinguishing marks that are considered in connection with him is impressed upon our mind. For as soon as we hear the sound of this designation, we immediately think of the son of Jonah, the man from Bethsaida, the brother of Andrew, the one summoned from the fisherman to the ministry of the apostolate, the one who because of the superiority of his faith was charged with building up the church. None of these is his substance, understood as subsistence. Hence the name determines for us the character of Peter. It cannot ever communicate the substance itself. (Eun. 2.4)
A proper name specifies an individual existent by the implicit invocation of identifying descriptions or characteristics. (Is Basil proposing a descriptivist theory of proper names?) When we hear a proper name, we immediately think of the referent’s distinctive features. The name does not tell us what it is. It helps us, rather, to identify the referent and to separate it from other objects of its kind. The trinitarian titles function like proper names; hence, Basil concludes, “in the case of both ‘Father’ and ‘Son’ the names do not communicate substance but instead are revelatory of the distinguishing marks” (Eun. 2.5).
Basil offers his fullest exposition of the idiomata later in Book 2:
If anyone wants to accept that which is true, namely, that begotten and unbegotten are distinctive features that enable identification and are observed in the substance, which lead to the clear and unconfused notion of the Father and the Son, then he will escape the danger of impiety and preserve logical coherence in his reasoning. The distinctive features, which are like certain characters and forms observed in the substance, differentiate what is common by means of the distinguishing characters and do not sunder the substance’s sameness in nature. For example, the divinity is common, whereas fatherhood and sonship are distinguishing marks: from the combination of both, that is, of the common and the unique, we arrive at comprehension of the truth. Consequently, upon hearing ‘unbegotten light’ we think of the Father, whereas upon hearing ‘begotten light’ we receive the notion of the Son. Insofar as they are light and light, no contrariety exists between them, whereas insofar as they are begotten and unbegotten, one observes the opposition between them.
It is the nature of the distinguishing marks to show otherness in the identity of the substance. And as for the distinguishing marks themselves, while they are often contradistinguished from one another such that they are separated to the point of being contraries, they certainly do not rupture the unity of the substance, as with the winged and the footed, the aquatic and the terrestrial, and the rational and the irrational. Since there is one substance that underlies all of them, these distinguishing marks do not make the substance foreign to itself, nor are they persuaded to join each other in a kind of rebellion. They implant the activity of the things they identify as a kind of light in our soul, and guide to an understanding attainable by our minds. … Begottenness and unbegottenness are distinctive features that enable identification. If there were nothing that characterized the substance, there would be no way for our understanding to penetrate it. Since the divinity is one, it is impossible to receive a notion of the Father or the Son that distinguishes each, unless our thinking is nuanced by the addition of the distinguishing marks. (Eun. 2.28-29)
The Father is unbegotten ousia; the Son is begotten ousia. “The difference between Father and Son,” Hildebrand explains, “lies not in substance but in number and in the properties that characterize each” (p. 65). God is apprehended as trinitarian when we combine the common divinity and the distinctive properties. This may be a weakness in St Basil’s early analysis, suggests Hildebrand. At this point all Basil can say is that the Father is ousia plus fatherhood and the Son is ousia plus sonship (p. 67). The great hierarch needs a word to denote the distinctive identities of the Father, Son, and Spirit.