Summa summae S. Thomae sive compendium theologiae

Subsistence implies four things: 1° singularity, for things do not subsist in the universal; 2° a mode of existing through itself, independently of another sustaining it, which is called the perseity of independence; 3° a mode of existing incommunicably, or the incommunicability of a nature as suppositized and terminated to another term and supposit, which is called the perseity of incommunicability; 4° the very concrete instance of the nature by way of one possessing it, and as the quod-principle of operations.

I say, first: In God, considered in himself and with the relations and persons prescinded from, there is given an absolute subsistence, which exists through itself, independently of another sustaining it, and constitutes the quod-principle of acting.¹

So Augustine, book 7 of On the Trinity, chapter 4; Jerome, Letter 57, to Damasus; Cyril of Alexandria, and others, but above all Saint Thomas, cited in the margin.

Proof. God, considered in himself and with the relations and persons prescinded from, truly subsists. But not by a relative and personal subsistence. Therefore by an essential and absolute subsistence. — The minor is clear. — The major, in which the difficulty lies, is proved in several ways.

First: God, considered in himself as prescinded from the persons, creates and works ad extra — otherwise the works of the Trinity ad extra would not be undivided; likewise he is understood as understanding and willing in that prior consideration. Therefore he is also understood as subsisting. — The consequence is clear, since, subsistence being a substantial act, it belongs to the nature prior to operation, which by common concept is not a substantial act. Whence Saint Thomas says below, q. 75, a. 2, o.: "Nothing can operate through itself, except what subsists through itself." And that common axiom: "Actions belong to subsisting things."

Second: To subsist expresses the greatest perfection; for it expresses the most perfect mode of being. But every perfection belongs to God considered in himself, with the persons prescinded from. Therefore. — The minor is clear, both because God, considered in himself and prescinded from the relations, is pure and infinite act, being itself in itself and from itself, independently of anything else; and also because he draws no perfection from the relations, as we said above, but rather bestows his own upon them. Therefore.

Third: To be, or to exist through itself, belongs to God antecedently to the persons. Therefore also to subsist. — The consequence is clear, because by absolute subsistence we understand nothing other than the perseity of independence, that is, to exist through oneself; and elsewhere, in the principles of Saint Thomas, existence presupposes subsistence, for to exist through oneself is the act of a subsisting thing. — The antecedent, moreover, is manifest; for existence is something absolute, indeed the very essence of God, apart from any virtual distinction.

For the solution of objections, note that the adversaries do not deny that God, prescinded from the persons, exists through himself independently of anything else, and is the quod-principle of operations; but they deny that the formality by which he is such a constitutive can be called subsistence, because it does not afford incommunicability. We, however, say that it can be called subsistence — not simply, but with a qualification: absolute subsistence, or, if you prefer, inadequate subsistence — both because the holy Fathers spoke thus, and because, although the divine relation does not afford the perseity of independence, it is nonetheless called subsistence by the adversaries themselves, because it affords the perseity of incommunicability. Why, then, should not the formality of which we speak be called subsistence, since, although it does not afford the perseity of incommunicability, it nonetheless affords the perseity of independence, and the character of a quod-principle in acting? But since this is a question of terminology, I do not dwell on it longer.

I say, second: Besides absolute subsistence, there are in God three relative and personal subsistences.

So Saint Thomas here, q. 29, a. 2, ad 2, where he says: "Just as we say, in the plural, three persons and three subsistences in the divine, so the Greeks say three hypostases." And below, q. 40, a. 3, ad 2: "By paternity the Father is not only Father, but is a Person, and is a someone, or hypostasis."

The first argument, a priori. According to the Catholic faith, there are in God three persons, three hypostases, three supposits. But person, hypostasis, and supposit are formally constituted by subsistence. Therefore there are in the divine three subsistences. — Proof of the consequence. For the multiplication of a substantive noun, such as supposit and person, the multiplication of the form is required. Whence, if there were in God but a single subsistence, even if modified by three relations — just as there is a single nature modified by three relations — we could no more say that there are three persons in the divine than three gods, but we would be bound to acknowledge a single person, on account of the unity of subsistence. Indeed, we could not even say three subsisting beings adjectivally, as we now say three divine beings, because adjectival names are not multiplied unless the supposit is multiplied — for example, the same man having several skills is not called several craftsmen; and if subsistence were not multiplied, the supposit, which subsistence formally constitutes, would not be multiplied, as we said just now.

The second argument, a priori. It belongs to the nature of subsistence as such — insofar as it abstracts from the communicable and the incommunicable — to render the nature as having being by way of a subsisting whole, and as a quod-principle of acting; for as the common axiom holds, "actions belong to subsisting things." And for this reason we admit in God, prescinded from the persons, an absolute subsistence, by which the quod-principle of the essential and common actions is constituted. But in God there are not only operations that are essential and common to the whole Trinity, but also notional² operations, proper to the divine persons — such as to generate, for the Father; to breathe forth, for the Son; to be breathed forth, for the Holy Spirit. Therefore there must be given, not only diverse modes of incommunicability, but true and distinct relative subsistences, by which are constituted distinct quod-principles of these notional actions — namely, the Father as the quod-principle of active generation, the Son as the quod-principle of active spiration, and indeed the Holy Spirit as the qui-term of this spiration: because, just as the quod-principle, so also the qui-term of this action must be subsisting; for just as actions, so too passions, or quasi-passions, belong to subsisting things.

The third argument, taken a posteriori from the mystery of the Incarnation. The human nature was united to the Word, not in something common to himself and the other persons — otherwise the three persons would be incarnate — but in something proper to himself. But it was united in his personal subsistence, supplying the place of created subsistence. Therefore there is given in the Son a personal subsistence virtually distinct from the absolute; and if in the Son, then by the same reasoning in the Father and the Holy Spirit as well.