108. The Agent Intellect: Unity and Multiplicity

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Lecture Notes

Main Topics #

The Problem: Unity vs. Multiplicity of the Agent Intellect #

• Question 79, Article 5 asks whether the agent intellect (ἀγεννήτως νοῦς / intellectus agens) is numerically one in all humans or multiplied according to the multiplication of souls
• This concerns the metaphysics of how immaterial powers relate to material multiplicity
• Connection to the previous article (4): the agent intellect was established as a power of the soul, not a separated substance

The Question of “One” and Unity #

• Heraclitus’s fragment about all things being one can mean either:
  • Each thing is unified in itself (unity of composition)
  • All things share unity of origin or order in the universe
• The term “one” has multiple senses and must be carefully distinguished
• Understanding the same thing does not require having numerically the same intellect

The Separated/Non-Separated Distinction #

• The agent intellect is called “separated” because it is not the act of any bodily organ
• This does NOT mean it is a “separated substance” (substantia separata) like an angel
• Angels are truly separated substances—independent immaterial beings
• This distinction is crucial for understanding why multiplicity does not follow from immateriality

Key Arguments #

Objections to Individual Agent Intellects #

First Objection:

• Premise: Nothing separated from body is multiplied by the multiplication of bodies
• Premise: The agent intellect is separated (immaterial)
• Conclusion: Therefore the agent intellect is not multiplied but is one in all men

Second Objection:

• Premise: The agent intellect causes universals (which are one in many)
• Principle: What causes unity must itself be more unified (ratio: if sugar makes coffee sweet, sugar must be sweeter)
• Conclusion: Therefore the agent intellect must be numerically one in all

Third Objection:

• Observation: All men assent to the same first principles (e.g., “a whole is greater than a part”)
• Inference: This common understanding suggests one agent intellect in all
• Example given: Someone denying the whole is greater than a part in theory, but expecting full payment rather than partial payment, contradicts themselves in action

Thomas Aquinas’s Resolution #

Core Principle: No single power (in number) can exist in diverse substances

• Since the agent intellect is established as a power of the soul (Article 4)
• And souls are multiplied according to the multiplication of men
• Therefore there must be many agent intellects, not one

Against First Objection:

• Aristotle proves the agent intellect is separated through the possible intellect being separated
• The possible intellect is separated because it can receive all material natures without having any material nature itself (like an eye without color to see all colors)
• The agent intellect is likewise immaterial because it acts on material phantasms
• But “separated” here means “not the act of a bodily organ,” not “separated substance”
• This is how both the possible and agent intellects are separated without being separated substances like angels

Against Second Objection:

• The agent intellect causes the universal “by abstraction or separation from matter”
• For the universal to be one in many requires the agent intellect to be one AS A KIND, not numerically one in all
• Each human has their own agent intellect, but all are of the same kind
• All relate to the same intelligible forms that they abstract from phantasms

Against Third Objection (implied):

• Universal agreement on first principles comes from:
  • The same kind of power in all human beings
  • The same nature (human nature shared by all)
  • The same ultimate source in God (all agent intellects are derived from divine light)
• This explains agreement without requiring numerical identity

Important Definitions #

Agent Intellect (intellectus agens / νοῦς ποιητικός)

• The active power of the human soul that makes potentially understandable things actually understandable
• Acts on phantasms (imagination-produced images) to abstract universal intelligible forms
• Compared to light that illuminates colors, making them visible
• Distinguished from the possible intellect (receptive power)

Separated Substance (substantia separata)

• An immaterial substance existing independently of matter
• Examples: angels, God
• The agent intellect is NOT a separated substance but a power of the individual soul
• This distinction is central to Thomas’s refutation of Avicenna

Universal (universale)

• One intelligible form found in many particulars
• Abstracted by the agent intellect from material, singular phantasms
• Differs from the particular in having no material conditions

Separated (separatus) - Two senses:

1. Not the act of a bodily organ (applies to agent intellect)
2. An independent immaterial substance (does not apply to agent intellect, only to angels)

Examples & Illustrations #

The Salary Example

• If someone is paid only part of their salary instead of the whole, they protest
• This demonstrates that all humans naturally understand “a whole is greater than a part”
• Yet this universal agreement does not require one numerically identical intellect
• Shows the sophistry of those (like Bertrand Russell) who deny this principle

The Light Analogy (Aristotle)

• The agent intellect is like light illuminating colors
• There is not the same light in diverse things illuminated
• Just as multiple objects can be illuminated by light without the light being divided or multiplied
• Contrasts with Plato’s sun analogy, where the sun is a separated substance

The Teacher and Student Example

• Father Bourlay remarked that “nobody can teach somebody else’s course” the same way
• Two professors may teach identical material but in entirely different ways
• Shows individual variation even when working with the same content
• Illustrates how multiplicity of intellects is compatible with unity of understanding

The Trinity Analogy

• God the Father, Son, and Holy Spirit have one mind literally
• Yet they are three divine persons
• Shows that unity is compatible with plurality in a higher order
• The early church spoke of believers having “one soul” (unanimous = “one soul”) without being literally one soul

Questions Addressed #

Q: If the agent intellect makes the universal (which is one in many), must the agent intellect itself be one in all humans?

A: No. The agent intellect must be one as a kind of power, and each agent intellect is one in its own individual soul. The unity of the universal comes from the immaterial nature of the agent intellect’s activity, not from numerical identity of agent intellects across humans. Just as light illuminates many objects without being numerically multiplied, so the agent intellect abstracts one universal from many particulars without requiring numerical unity across different souls.

Q: How can all humans agree on first principles (like “a whole is greater than a part”) if they have different agent intellects?

A: Agreement comes from three factors: (1) All humans share the same kind of power (agent intellect as a power); (2) All humans share the same nature (human nature); (3) All agent intellects are ultimately derived from the same divine source. Numerical identity is not required for universal agreement on self-evident principles.

Q: Is the agent intellect truly a power of the individual soul if it is in some sense derived from God?

A: Yes. The soul itself is created by God, and powers flow from the essence of the soul. Therefore, the agent intellect, as a power of the soul, is both a power of the individual soul AND ultimately derived from God. There is no contradiction between these—the creature’s power is the creature’s mode of participation in divine power.