Anyway, there are different senses of hypostasis and ousia so let's look at it here:
The term ‘ὑπ όστασις’ had two basic groups of usages in the Greek language: “in one group of usages the term derives its purport from the middle voice of the verb ὑ φίστημι , and in another from the active voice. Hereafter it may mean either that which underlies, or that which gives support” (Prestige 163). In the former sense the term is synonymous with the term Ousia; “it meant a single object of which the individuality is disclosed by means of internal analysis, an object abstractly and philosophically a unit” (Prestige 163-167). In its second sense though, the term ‘ὑπ όστασις’ had a different emphasis; “here the emphasis falls not on the content but externally concrete independence, objectivity in relation to other objects” (Prestige 168-169). In all probability, the second sense was unknown to the Westerners; therefore, when hearing ‘ὑπ όστασις’, Westerners thought of Ousia, and not something like persona (Prestige, 1959). Still the potential for misunderstanding was enormous, because it was not enough to claim the unity of God, or the equality of the hypostases or personæ. It was necessary to explain the words from Scripture which ascribed to each of the three one particularity: ἀγεννησία, γέννησις and ἐκπόρευσις. The distribution of these particularities, though, could only make sense when holding on to the principle of monarchy; yet, how could this monarchy be explained? If the monarchy was rooted in the hypostasis of the Father, did not then the idea of eternal co-sharing of Ousia [wealth - Soror] by the other two hypostases allow for the principle of monarchy to be situated in the common Ousia [wealth - Soror]? Most likely, it was at exactly this point that the two theological traditions took two different paths. One was expressed by the Cappadocians, who alleged that the monarchy of the hypostasis of the Father constituted the key to the elaboration of the doctrine (Alexopoulos 150), while the other tradition, expressed by Augustine, referred to the unity of God—‘una substantia’—as the fundament of the Trinitarian doctrine (McKenna, 1963)...
...The terminological tradition of the Cappadocians advanced “the position of the objective triplicity of God as the basis of their thought, and from there, having presumed the equality of the three hypostases, went to the assertion that these three hypostases must constitute a single identical Ousia [wealth - Soror]” (Prestige 242). Yet, why was this order of thought of great importance for them? Clearly, this notional prerequisite for the further doctrinal elaboration was concerned with stating the ontologisation of the category of person, an idea derived from the Scriptural source. This means that the Cappadocians’ terminology overcame the division between person and substance by having construed the category of person/hypostasis as an ontological rather than as a functional entity (Colins 144). The category of person was by no means a passive attribute/accident of the being/Ousia [wealth - Soror]; instead, it was an active owner of being [wealth - Soror](Alexopoulos 154). For this reason the Cappadocians use the doctrine of ἀρχή, according to which there is a logical, but not a temporal priority between three divine Persons; the divine ὑπόστασις of the Father (ἀγέννητος) is not superior to the hypostases of the Son and the Holy Spirit with reference to their modes of existence (γεννητός, ἐκπορευόμενος) (Prestige 245-249). Basil’s treatise (de Spir. Sanct. 63)advances this idea considerably; he describes the relationship between the divine Persons by using the phrase “be with” (συνεῖναι) instead of “be in” (ἐνεῖναι). Heat, for instance, is said to reside ‘in’ a hot iron (from which it is separable) but ‘with’ the actual fire. Of course, the explicit intent of this metaphor is to express the intimate, inherent, and inseparable relation between the divine Persons. Implicitly, however, it underlines the objectivity of the divine Persons (against any monistic representation) and their equality (against any subordinationism). Yet, this idea of Basil the Great was often misrepresented as an inauspicious slide of his doctrinal elaboration into pluralism/tritheism (Prestige 282-287). Resulting from this misunderstanding, tritheism was often imputed to the Cappadocian Fathers; such imputations, however, strike as naïve unwarranted conclusions, because Cappadocians complied their metaphors of three distinctive hypostases with the conception that divine Persons contain each other (χωρητικός, περιέχεσθαι) (Gregory of Nyssa, Adv. Ar. Et Sab. 12). According to this concept, each hypostasis makes a headway in the next hypostasis (from the Father through the Son to the Holy Spirit) and simultaneously a back motion (from the Holy Spirit through the Son back to the Father), because the hypostases are receptive and permeative with each other (Prestige 289). Thus, a new ontology developed in which being God means to be in communion (Zizioulas, 1985). Orthodoxy is only preserved in such terms.
