141. Avicenna and Plato: Theories of Intelligible Forms

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Lecture Notes

Main Topics #

• Avicenna’s Position: Intelligible forms do not subsist by themselves (contra Plato) but pre-exist immaterially in separated substances (angels). These forms flow into the human soul through a lowest separated substance called the “agent intellect.”
• Comparison with Plato: Both theories hold that intelligible forms originate from separated sources, but Plato claimed forms subsist independently while Avicenna located them in divine or angelic minds.
• The Problem of Soul-Body Union: If the soul receives all intelligible forms from separated substances, why would it need to be joined to a body at all?
• Sensory Necessity: Thomas argues that the senses are essential causes of human knowledge, not merely incidental arousal devices.
• The Agent Intellect: Aristotle’s agent intellect is a power of the soul (not a separated substance) that abstracts intelligible forms from sensible images.

Key Arguments #

Arguments Supporting Avicenna (Objections) #

First Objection (Based on Immateriality)

• The understanding soul, being immaterial, must partake of things that are essentially understandable
• Things actually understandable in their very nature must be the cause of the understanding’s intelligible forms
• Immaterial forms existing without matter are the only things actually understandable in act
• Therefore, intelligible forms must come from separated forms

Second Objection (Analogy with Sensation)

• Just as sensible things outside the soul cause sensible forms in the senses, so there must be understandable things outside the soul causing intelligible forms in the understanding
• These understandable things cannot be sensible things themselves (which are material) but must be forms existing in separation from matter
• Therefore, intelligible forms flow from separated substances
• Thomas’s Response: The analogy is overextended. Material things are actually sensible but only potentially understandable. They must be abstracted from sensibility to become actually intelligible through the agent intellect.

Third Objection (From Potency to Act)

• The understanding begins in potency (like a blank tablet) and is brought to act
• Whatever is brought from potency to act must be caused by something in act
• Therefore, an understanding always in act—a separated intellectual substance—must cause our intelligible forms
• Thomas’s Response: The agent intellect (a power of the soul) is in act and reduces our possible intellect from potency to act. This does not require a separated substance as a proximate cause, though all intelligible forms derive ultimately from God as remote cause.

Thomas’s Refutation of Avicenna #

The Inexplicability of Soul-Body Union

• If the soul receives intelligible forms solely from separated substances, the body becomes superfluous for understanding
• The soul’s union to the body would be without purpose or cause
• This violates the principle that form is for the sake of matter and act for the sake of potency, not the reverse

The Blind Man Objection

• A person born blind cannot know colors, proving sensory experience is necessary
• If forms flowed from separated substances independent of sensation, the blind should be able to know colors through that source alone
• The failure of this consequence refutes Avicenna’s position

Against the “Arousal” Defense

• Avicenna’s claim that senses merely arouse the soul to receive forms from separated substances is insufficient
• Such arousal would only be necessary if the soul were somehow stupefied by union with the body (as Plato believed)
• But there is no philosophical justification for this Platonic claim about the body imprisoning the soul
• Moreover, arousal through one sense cannot awaken knowledge of sensibles proper to another sense lacking in the person

Important Definitions #

Intelligible Form (Species intelligibilis)

• The immaterial representation by which the understanding understands actual things
• Must be separated from the singularity and materiality of sensed or imagined things to be actually understandable
• Differs fundamentally from sensible form, which retains material conditions

Agent Intellect (Intellectus agens)

• In Aristotle and Thomas: a power of the human soul that makes potentially intelligible things actually intelligible
• Compared to light illuminating potentially visible colors
• NOT a separated substance or angel (contra Avicenna)
• Acts upon the possible intellect by abstracting universal, immaterial forms from sensible images

Possible Intellect (Intellectus possibilis)

• The receptive power of understanding, initially in potency to all intelligible forms
• “Like a tablet upon which nothing has been written”
• Actualized by the agent intellect acting on sensible and imaginable content

Separated Substance (Substantia separata)

• In Avicenna: an immaterial being (angel) existing apart from matter
• In Plato: independently subsisting forms themselves
• Avicenna’s agent intellect is identified as the lowest separated substance from which forms flow to all human souls

Monopsychism

• Avicenna’s doctrine that there is one agent intellect shared by all human beings
• Each soul receives forms from this single separated substance
• Contrasts with Aristotle’s view that each human has his own agent intellect as a power of his individual soul

Examples & Illustrations #

The Blank Tablet (Aristotle’s Image)

• The understanding is like an unwritten tablet
• It begins in potency and is brought to act through experience and abstraction
• Demonstrates that human knowledge is not innate but acquired

The Christmas Cookies (Potency to Act)

• Dough in potency can be formed into various shapes (cookie, bell, tree)
• The baker (acting as agent in act) reduces the dough from potency to act
• Analogously, the agent intellect reduces the possible intellect from potency to intelligibility in act

The Blind Man and Colors

• A person born blind has no knowledge of colors despite possessing other senses and intellectual capacity
• This shows that sensation is a necessary cause, not merely incidental
• Refutes Avicenna’s claim that forms flow to the soul from separated substances independent of sensation

Heraclitus’s Fragment: “Listen not to me but to reason”

• “It is wise… to agree that all things are one”
• Demonstrates the principle of attending to common reason rather than individual speakers
• Used to illustrate the idea that truth is universal and transcends individual perspectives
• Connected to Augustine’s doctrine about seeing truth in that which is above our minds

Questions Addressed #

Why does the soul need a body if it receives intelligible forms from separated substances?

• Thomas’s answer: The soul must be joined to a body because knowledge naturally begins with sensible experience. Intelligible forms must be abstracted from sensible and imaginable content. Without sensation, understanding would have no proper material to work upon. The body is essential to the soul’s natural operation in this life.

Can sensory deprivation be compensated by receiving forms from separated substances?

• No. One born blind cannot know colors, and someone lacking one sense cannot know sensibles proper to that sense. This proves the senses are necessary causes, not merely arousing mechanisms. If separated substances supplied forms directly, sensory defects would be irrelevant.

Is there a difference between how Plato and Avicenna understand the source of intelligible forms?

• Yes. Plato claimed forms subsist by themselves, independent of any mind. Avicenna located forms in separated intellectual substances (angels), from which they flow like divine ideas. Both agree forms come from separated sources, but locate them differently.

Does Thomas deny that intelligible forms ultimately derive from separated sources?

• No. Thomas agrees that all intelligible forms are ultimately derived from God (the first cause who is purely intelligible in act). However, they are made actually intelligible for the human soul through the agent intellect’s abstraction from sensible images, not by direct influx from separated substances. God acts as remote cause; the agent intellect acts as proximate cause.

How does the possible intellect move from potency to act?

• Through the agent intellect, which is a power of the soul in act. The agent intellect abstracts intelligible forms from sensible and imaginable content, thereby actualizing the possible intellect. This is an immanent activity within the soul, not an external action by a separated substance.

Notable Quotes #

“The received is in the one receiving, according to the manner of the one receiving.” - Principle governing how immaterial understanding receives material forms immaterially.

“Things have to be separated from matter before they can be understood.” - Berquist, summarizing the condition for actual intelligibility.

“Therefore, understandable forms by which our understanding understands are caused by some separated substances.” - Avicenna’s conclusion, which Thomas refutes.

“What’s primarily understandable for us is not something understandable in act. What’s primarily understandable for us is that which is something sensed or imagined.” - Thomas’s key distinction limiting the analogy between sensation and understanding.

“Listen not to me but to reason.” - Heraclitus, cited to show that truth is common and universal, transcending individual speakers.

“If both you and I see that it is true what you say and we both see that it is true what I say, where do we see that? Not surely I and you, nor you and me, but both in that which is above our minds, in that unchangeable truth.” - Augustine, Confessions 12, cited regarding how truth itself is above individual minds.