53. The Unity and Existence of Christ

Summary

This lecture examines the metaphysical foundations of Christ’s unity as one person in two natures, focusing on Questions 17 of the Summa Theologiae. Berquist explores how to properly speak of Christ using Aristotelian distinctions between hypostasis/suppositum (that which subsists) and nature (that by which something is), and addresses the critical theological problem of whether Christ has one or two existences (esse), using the analogy of the human soul and body to illuminate the hypostatic union.

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Lecture Notes

Main Topics #

The Question of Christ’s Unity (Q. 17, Art. 1) #

Whether Christ is one or two given the union of divine and human natures
The problem: Christ has two natures, yet the Christian faith affirms he is one person
Heretics (Nestorians) posited two persons; the orthodox position affirms one hypostasis (ὑπόστασις)
The key distinction: duality in nature versus unity in person/hypostasis

The Metaphysical Distinction: Suppositum and Nature #

Suppositum (or hypostasis): that which subsists in itself; the underlying subject
Nature: that by which something is (id quo aliquid est); signified as form
A person is defined as a suppositum of rational nature
In Christ: one suppositum subsists in two natures
The predicate (which denotes nature) functions formally, like form to matter

Proper Speech About Christ #

We cannot say Christ is “two” without qualification (simpliciter), only with qualification (secundum quid)
We may say Christ is “two according to nature” but never “two persons” or “two supposita”
The word “both” (utrumque) must be understood on the side of the subject, not the predicate
This follows Augustine’s interpretation: “both God and man” refers to two natures in one subject, not two substances

The Problem of Christ’s Existence (Q. 17, Art. 2) #

Whether Christ has one esse (existence) or two
Objection: Things following upon nature are doubled in Christ; to be (esse) follows upon nature; therefore two beings
Objection: The divine being is eternal; the human being is temporal; therefore two distinct existences
The key distinction: Esse pertains to the hypostasis as “that which has existence” and to nature as “that by which something is”

The Resolution: One Esse Simply #

Because Christ has one hypostasis, he has one esse simply (simpliciter)
The human nature does not give Christ a new personal existence
Rather, the pre-existing divine existence is now related to human nature through hypostatic union
The human nature “participates” in the divine being
Analogy: Just as the body shares the soul’s existence (the soul makes the body animated in act), the human nature shares the divine existence

The Body-Soul Analogy #

The human soul has an existence independent of the body (demonstrated by intellection of universals)
Yet body and soul form one thing—a human being
The body does not have its own separate existence but shares in the soul’s existence
Aristotle: The human soul does not come from parents but is infused by God
Similarly, the human nature of Christ does not possess a separate personal being but is assumed by the eternal Person of the Word

Key Arguments #

For Christ’s Unity (Contra the Nestorians) #

Boethius’s principle: Every being, insofar as it is, is one (omne quod est, inquantum est, unum est)

Being and unity are convertible (convertibilia)
If Christ were two, he would not be one being
If he is one being, he must be one

The logic of predication: In a proposition, the predicate relates to the subject as form to matter

When we say “Christ is both God and man,” the predicate (the nature) is divided, not the subject
We divide universals into particulars by placing particulars below the universal, as matter below form
The agent acts upon the patient (matter), and gives it form
Therefore, what is universal (like nature) must be placed above the particular, or as form

For Distinguishing Nature from Person #

Augustine’s interpretation: “Other (ἄλλο/aliud) and other (ἄλλο/aliud)” in Christ must be understood as diversity of natures, not of supposita

The Latin word aliud (neuter: other) denotes diversity of substance
Yet it is specifically diversity of nature, not of hypostasis
Alios (masculine: another) would denote diversity of person—but this is false
Therefore: Christ is “aliud et aliud” (two in nature) but not “alios et alios” (two in person)

For One Esse in Christ #

From hypostatic union: Because Christ has one hypostasis and two natures, things pertaining to nature are two, but things pertaining to the hypostasis are one only

To be pertains to the hypostasis as that which possesses existence
To be pertains to nature as that by which something possesses existence
Nature is signified as form (e.g., humanity is that by which someone is human)
Therefore, the human nature does not bring Christ a new esse, but the divine esse now subsists in both natures

The distinction of esse: Not all to-be belongs to the personal existence of the hypostasis

To be white is a to-be of Socrates, but not his personal to-be (only insofar as he is white)
Similarly, there can be multiple such accidental or dependent existences in one hypostasis without multiplying the personal being
But the esse of the hypostasis itself—the personal being—cannot be multiplied in one person

The comparison to acquired perfections: If human nature came to Christ accidentally (as some heretics posited), it would require a new being

But because human nature is hypostatically united—truly assumed by the Person of the Word—it does not give a new personal being
It is like an organ joined to a body: when an eye is given to one born blind, this does not create a new being simply, but only a new relation to existing being
The human nature similarly participates in the pre-existing divine being through being assumed into the unity of the divine person

Important Definitions #

Hypostasis (ὑπόστασις) / Suppositum #

That which subsists in itself; a complete, individual substance
That which is complete and separate from others
The underlying subject in which natures inhere
In the incarnation: the single hypostasis is the divine person of the Son

Nature (natura) #

That by which something is; the essence or essential form
Signified formaliter (as form), not as the thing possessing it
In Christ: two natures—divine (eternal, uncreated) and human (temporal, created)
Nature pertains to the essence; it answers the question quid est (what is it?)

Person (persona) #

A suppositum of rational nature (Boethian definition)
In the incarnation: there is one person—the divine Word
The human nature does not constitute a separate person because it does not subsist by itself (per se) but in and through the divine person

Esse (εἶναι in Greek, esse in Latin) #

Existence; to be; the act of being
Pertains to the hypostasis as that which possesses existence (id quod est)
Pertains to nature as that by which something possesses existence (id quo est)
In Christ: one divine esse, not multiplied despite the two natures

Convertible (convertibilia) #

Predicates that can be turned around in definition
Being and one are convertible: every being is one; every one is a being
Like square and equilateral-right-angled-quadrilateral
Aristotle teaches this in Metaphysics IV (the book on wisdom)

Examples & Illustrations #

The Tower and the Child #

Berquist recalls watching his nephew: when shown a small tower, the child would knock it over. But when Berquist built a tower taller than the child, the child looked up in wonder and did not disturb it.

Point: Why? Because a lower agent can act on a higher patient, but a lower patient cannot easily act on a higher agent.
Application to logic: This is why we place the particular under the universal, the agent above the patient—it reflects the structure of action and passion (ἐνέργεια/πάσχειν)

The Whiteness Analogy #

To be white is a being of Socrates, but not Socrates’ personal being—only “insofar as he is white.”

Multiple such dependent existences (to be white, to be musical) do not multiply the one personal being
But the being of the hypostasis itself cannot be multiplied
Application: Similarly, the human nature’s relation to existence does not create a new personal being in Christ, but shares the pre-existing divine being

The Soul Giving Being to the Body #

The body shares in the existence given by the soul.

The soul animates the body; by the soul, the body is animated in act
Yet there is one human being, not two
Application: The human nature of Christ, assumed by the divine person, similarly shares in divine existence; the divine being now subsists in both natures

When one born blind receives eyes, this does not create a new being simply (simpliciter).

The person’s being is not newly constituted
Rather, a new relation to pre-existing being is established
Application: The assumption of human nature by Christ similarly establishes a new relation (the divine person now subsists in human nature) but does not create a new personal being

Notable Quotes #

“Every thing, according as it is said to be being, is said to be one.” (From Aristotle, applied by Thomas)

“One and being are convertible” (omne quod est, inquantum est, unum est)

“To be follows upon nature, not as having to be, but as that by which something is; but it follows upon the person or hypostasis as the one having existence.” (Thomas, in response to the first objection)

“The human nature in Christ was a tool of the divinity.” (Referenced as Thomas’s teaching in Summa Contra Gentiles)

“The soul gives to be or existence to the body insofar as it makes it to be animated in act.” (Thomas, on the analogy of incarnation)

Questions Addressed #

Q1: Is Christ one or two? #

Position: Christ is one person (one hypostasis/suppositum) but two natures.

Resolution:

The duality pertains to nature; the unity pertains to person
When we say Christ is “both God and man,” we refer to two natures in one subject
We cannot say simply “Christ is two” (that would imply two persons)
We can say “Christ is two according to nature” (secundum quid, with qualification)
The heretical error was to affirm two persons (Nestorianism)

Q2: Does Christ have one or two existences (esse)? #

Position: Christ has one existence simply (simpliciter)—the divine esse.