7. The Union of the Incarnate Word in Person, Not Nature

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Lecture Notes

Main Topics #

The Question at Hand #

• Whether the union of the Incarnate Word was made in one nature or in one person
• Central to understanding the Council of Chalcedon’s formulation: “without confusion, without change, without division, inseparably”
• Cyril of Alexandria and the Athanasian Creed appear to speak of “one nature” of the incarnate Word, requiring clarification

The Meaning of “Nature” #

Thomas begins by establishing six distinct meanings of the term natura:

1. Birth itself (nativitas) - the phenomenon that prompted the word’s original usage
2. Source of birth within the mother - the word carried over (translatum) from the first meaning
3. Any intrinsic principle of motion or change - Aristotle’s definition in Physics II.1: “a beginning of motion in that which it is, intrinsic, as such and not by happening”
4. Matter (passive principle) - illustrated by wood vs. stone in fire
5. Form (active principle) - illustrated by the tree growing but stone not growing
6. The essence of a species; what a thing is (quiddity) - Boethius’s definition of nature as “the specific difference forming each thing, making it to be what it is”

For purposes of this discussion, Thomas uses nature in the sixth sense: the essence or whatness of a thing.

Three Impossible Modes of Union #

Thomas demonstrates through division (per disjunctionem) that there are only three ways two things can unite to form one:

First Mode: Union of Perfect Integral Parts (Without Change) #

• Example: Stones forming a pile; wood forming a house
• Result: Only accidental unity (through composition, order, or figure), not substantial unity
• Problem: Composition, order, and figure are accidental forms, not substantial forms
• Conclusion: This cannot apply to the Incarnation, which requires substantial union, not merely accidental arrangement

Second Mode: Union Through Mixture or Change (Change Converting One Nature into Another) #

This mode is impossible for three distinct reasons:

1. Divine Immutability: God cannot be changed or converted into another nature. The divine nature is absolutely immutable (immutabilis).

2. Mutual Obliteration in True Mixture: In true chemical mixture, neither original species remains intact. Just as flesh differs from the constituent elements (earth, air, fire, water) that compose it, so any true mixture of divine and human natures would obliterate both original natures.

3. Infinite Disproportion: The divine nature infinitely exceeds human nature in perfection and power. In any union by conversion, the lesser is “swallowed up” by the greater—like a drop of water (gutta aquae) in an amphora of wine (amphora vini). The human nature would be consumed by the divine.

Symbolic Reference: The Burning Bush (rubum ardens) illustrates this principle: the fire (divine nature) does not consume the bush (human nature), demonstrating that divine nature can be present without destroying human nature.

Third Mode: Union as Form and Matter (Potential and Actual) #

• Why it cannot apply: Both divine and human natures are complete and perfect in themselves
• Divine nature cannot serve as the form of a body (already established in the Prima Pars)
• They cannot unite as quantitative or essential parts
• Result: Would produce a new mixed species, making Christ neither God nor man but something tertium quid (a third thing)

The Correct Union: In Person, Not Nature #

Definition of Key Terms #

Nature: Signifies the essence or species of a thing—what it is

Person: Following Boethius, “an individual substance of a rational nature” (substantia individua naturae rationalis). Person signifies the individual subsisting in that nature—the suppositum or hypostasis (in the sense of the underlying individual)

The Distinction in Composite Beings #

• In humans, person and nature differ
• The person is the whole (the individual human)
• The nature is the formal part (humanity)
• The person includes the nature plus individuating principles or accidents (particular knowledge, health, color, position, etc.)
• Example: “Duane Berquist” (the person) has human nature but is not human nature

In God #

• Person and nature are the same secundum rem (in reality)
• They differ only secundum rationem (in conception/reasoning)

The Incarnational Union #

• The human nature of Christ is united to the Word of God such that the Word subsists in it
• The human nature does not have its own personality (non habet personalitatem propriam)
• The human nature exists in the higher person of the Word
• This is why Christ is one person with two natures

Analogy: The Hand #

• A hand is an individual substance but not a person
• Why? Because it exists in something more perfect (the whole human body)
• Analogously, Christ’s human nature is an individual substance but does not constitute a separate person because it exists in the divine person

The Dignity of Christ’s Human Nature #

Crucial principle: It is greater dignity for something to exist in something more dignified than itself, than to exist per se (in isolation)

Example: Sensitive powers are more noble in human beings (where they serve the intellect) than in brute animals (where they are the highest completing form)

Application: Christ’s human nature has supreme dignity precisely because it lacks its own personality and exists in the divine person—infinitely more dignified than any created person

Key Arguments from Authorities Against Union in Nature #

First Objection: Cyril of Alexandria #

• Text: From the Council of Chalcedon, Cyril states: “It is not necessary to understand two natures, but the one nature of the incarnate Word”
• How Thomas addresses it: The Fifth Ecumenical Council explains this means God’s nature united flesh to his person, not that two natures became one nature. Cyril’s language must be understood in light of the conciliar clarification.

Second Objection: The Athanasian Creed #

• Text: “As the rational soul and flesh come together in the constitution of human nature, so God and man come together in the constitution of one nature”
• How Thomas addresses it: The analogy applies to union in person, not union in nature. Soul and body unite in a human person through both form/matter AND agent/tool relationships. The Incarnation parallels the agent/tool relationship (divine nature using human nature as its conjoined instrument), not the form/matter relationship.

Third Objection: Mutual Denomination #

• Text: Cyril: “The divine nature was made incarnate”; Gregory Nazianza: “The human nature was deified”
• Problem: When two natures are denominated from each other, don’t they suggest becoming one nature?
• Response: These predications are explained through the unity of person. The natures remain distinct but are mutually attributed to the one person.

Important Definitions #

• Natura: The essence or quiddity of a thing; what it is (quid est)
• Persona: An individual substance of a rational nature (substantia individua naturae rationalis) - following Boethius’s definition
• Suppositum: The underlying individual that subsists in a nature; equivalent to hypostasis in rational natures
• Hypostasis (ὑπόστασις): Etymologically “standing under” (stans sub), equivalent to substantia in Latin. Used by Greeks to mean person in the Trinity and in Christology.
• Translatum: A name “carried over” (translatio nominis) from one meaning to another through metaphor
• Secundum rem: In reality, actually
• Secundum rationem: In conception, in reasoning, mentally

Examples & Illustrations #

The Harassed Mother (Explaining Nature) #

A mother answering her child’s question “Why does the tree grow but the stone doesn’t?”:

• Her answer: “It’s the nature of the tree to grow; it’s not the nature of a stone to grow”
• What she’s really saying: Since the outside conditions are identical (same sun, rain, soil), the difference must come from something intrinsic within the thing
• This illustrates: Nature as an intrinsic principle of motion (principium intrinsecum motus)

Wood and Stone in Fire #

• The situation: Place wood in fire; it burns. Place stone in fire; it doesn’t burn.
• Why?: The same flames lick both, but one burns and one doesn’t. The difference comes from within.
• What this shows:
  • Wood has a nature (active principle/form) that can be acted upon by fire
  • Stone has a nature (passive principle/matter) that resists being acted upon by fire
• Illustrates: Nature as both active and passive principles

The Burning Bush (Divine Fire) #

• Symbol: Fire = divine nature; Bush = human nature
• The principle: The fire does not consume the bush
• The point: Divine nature, when present, does not swallow up or obliterate human nature (addressing the objection from infinite disproportion)

Questions Addressed #

1. Can two complete natures unite to form one nature?

   • Answer: No. Thomas proves this through three modes of union, all of which are impossible between divine and human natures.

2. What does the Council of Chalcedon mean by preserving “the difference of the natures”?

   • Answer: The two natures remain distinct in their properties and operations, united in one person.

3. How should we understand Cyril’s language about “one nature”?

   • Answer: It refers to union in person, clarified by the Fifth Ecumenical Council, not a confusion of natures.

4. Does Christ’s human nature lack dignity by lacking its own personality?

   • Answer: No. It has greater dignity by existing in the divine person than it could have existing per se.

5. Why must we focus on the distinction between nature and person?

   • Answer: This distinction is essential to understanding how Christ can be fully divine and fully human while remaining one person.