Of Christ's Unity of Being

Of Christ's Unity of Being — St. Thomas Aquinas asks: Whether Christ is one or two?; Whether there is only one being in Christ?.

We must now consider what pertains to Christ's unity in common. For, in their proper place, we must consider what pertains to unity and plurality in detail: thus we concluded () that there is not only one knowledge in Christ, and it will be concluded hereafter () that there is not only one nativity in Christ.

Hence we must consider Christ's unity (1) of being; (2) of will; (3) of operation.

Under the first head there are two points of inquiry:

Article 1: Whether Christ is one or two?

Boethius says (De Duab. Nat.): "Whatever is, inasmuch as it is, is one." But we confess that Christ is. Therefore Christ is one.

Nature, considered in itself, as it is used in the abstract, cannot truly be predicated of the suppositum or person, except in God, in Whom "what it is" and "whereby it is" do not differ, as stated in the . But in Christ, since there are two natures, viz. the Divine and the human, one of them, viz. the Divine, may be predicated of Him both in the abstract and in the concrete, for we say that the Son of God, Who is signified by the word Christ, is the Divine Nature and is God. But the human nature cannot be predicated of Christ in the abstract, but only in the concrete, i.e. as it is signified by the suppositum. For we cannot truly say that "Christ is human nature," because human nature is not naturally predicated of its suppositum. But we say that Christ is a man, even as Christ is God. Now God signifies one having the Godhead, and man signifies one having manhood. Yet one having manhood is differently signified by the word "man" and by the word "Jesus" or "Peter." For this word "man" implies one having manhood indistinctly, even as the word "God" implies indistinctly one having the Godhead; but the word "Peter" or "Jesus" implies one having manhood distinctly, i.e. with its determinate individual properties, as "Son of God" implies one having the Godhead under a determinate personal property. Now the dual number is placed in Christ with regard to the natures. Hence, if both the natures were predicated in the abstract of Christ, it would follow that Christ is two. But because the two natures are not predicated of Christ, except as they are signified in the suppositum, it must be by reason of the suppositum that "one" or "two" be predicated of Christ.

Now some placed two supposita in Christ, and one Person, which, in their opinion, would seem to be the suppositum completed with its final completion. Hence, since they placed two supposita in Christ, they said that God is two, in the neuter. But because they asserted one Person, they said that Christ is one, in the masculine, for the neuter gender signifies something unformed and imperfect, whereas the masculine signifies something formed and perfect. on the other hand, the Nestorians, who asserted two Persons in Christ, said that Christ is two not only in the neuter, but also in the masculine. But since we maintain one person and one suppositum in Christ, as is clear from[4066] , it follows that we say that Christ is one not merely in the masculine, but also in the neuter.

Article 2: Whether there is only one being in Christ?

Everything is said to be a being, inasmuch as it is one, for one and being are convertible. Therefore, if there were two beings in Christ, and not one only, Christ would be two, and not one.

Because in Christ there are two natures and one hypostasis, it follows that things belonging to the nature in Christ must be two; and that those belonging to the hypostasis in Christ must be only one. Now being pertains both to the nature and to the hypostasis; to the hypostasis as to that which has being---and to the nature as to that whereby it has being. For nature is taken after the manner of a form, which is said to be a being because something is by it; as by whiteness a thing is white, and by manhood a thing is man. Now it must be borne in mind that if there is a form or nature which does not pertain to the personal being of the subsisting hypostasis, this being is not said to belong to the person simply, but relatively; as to be white is the being of Socrates, not as he is Socrates, but inasmuch as he is white. And there is no reason why this being should not be multiplied in one hypostasis or person; for the being whereby Socrates is white is distinct from the being whereby he is a musician. But the being which belongs to the very hypostasis or person in itself cannot possibly be multiplied in one hypostasis or person, since it is impossible that there should not be one being for one thing.

If, therefore, the human nature accrued to the Son of God, not hypostatically or personally, but accidentally, as some maintained, it would be necessary to assert two beings in Christ---one, inasmuch as He is God---the other, inasmuch as He is Man; even as in Socrates we place one being inasmuch as he is white, and another inasmuch as he is a man, since "being white" does not pertain to the personal being of Socrates. But being possessed of a head, being corporeal, being animated---all these pertain to the one person of Socrates, and hence there arises from these only the one being of Socrates. And if it so happened that after the person of Socrates was constituted there accrued to him hands or feet or eyes, as happened to him who was born blind, no new being would be thereby added to Socrates, but only a relation to these, i.e. inasmuch as he would be said to be, not only with reference to what he had previously, but also with reference to what accrued to him afterwards. And thus, since the human nature is united to the Son of God, hypostatically or personally as was said above (), and not accidentally, it follows that by the human nature there accrued to Him no new personal being, but only a new relation of the pre-existing personal being to the human nature, in such a way that the Person is said to subsist not merely in the Divine, but also in the human nature.