The Timpson Lyceum · History of Philosophy (2024)

Aristotle's Metaphysics & Psychology – Lecture 27 (History of Philosophy)

Overview

Aristotle's psychology — literally the study of the psuchē, the soul — extends his metaphysics from things in general to living things in particular, and forms the second half of his account of knowledge (the first half, in the Organon, described how thought is structured once formed). The governing idea, set out in the De Anima, is hylomorphic: the soul is not a spirit trapped in a body but the form of a living body, its first actuality. A living organism just is matter (the body) organized by a life-principle (the soul); remove the soul and the body is a corpse. This decisively rejects Plato's dualism, in which soul and body are at war and the soul strives to escape — for Aristotle, embodied life is good, and only body-and-soul together can achieve a thing's full actualization.

From this single definition Aristotle builds a graded hierarchy of soul faculties — nutritive, sensitive, rational — each higher grade presupposing the lower, and matches it to a theory of perception and thought. Sensation is a dual actualization in which the sense organ takes on the sensible form of its object; the common sense unifies the streams into single perceptions; and the intellect (nous), split into a passive and an active part, takes in the forms of things themselves. The lecture closes on the two hardest points: why the passive intellect can have no prior structure of its own (a thesis that anticipates and answers Kant), and the obscure suggestion that the active intellect alone is immortal.

Key Concepts

Soul as the principle of life — The soul (psuchē) is what makes a thing alive; every living thing has one. It is not, in Aristotle's usage, the seat of personal survival — that role, insofar as any, falls to nous (mind/intellect). Possessing a soul is an essential property: strip it away and the thing is fundamentally something else (a corpse), not merely altered.
Hylomorphic soul — Soul is to body as form is to matter, as actuality is to potentiality. Aristotle's definition: the soul is "the first actuality of a natural body having life potentially in it." His analogies: the soul is like the stamp impressed on wax, or like the capacity for sight that stands to the eye as the eye's whole function.
First actuality vs. second actuality — The soul is a first actuality: a settled state or capacity (like knowledge one possesses even while asleep), distinct from its second actuality, the active exercise of that capacity (like actually contemplating). Life is present as the standing form of the organized body, not only when its powers are being used.
Against Platonic dualism — There can be no soul without a body and no metaphysical war between them. The soul is an aspect of a living entity, not an independent substance; it ceases when the body ceases to live. Being alive is good, and the body is the necessary partner in self-actualization.
The three grades of soul — Nutritive (vegetative): nutrition, growth, reproduction — the empirical mark of life, possessed by plants. Sensitive: adds perception, appetite, and self-generated locomotion — possessed by animals. Rational: adds thought, reflection, argument, and science — possessed by humans alone. Each grade is an essential part; reducing a human to a merely vegetative or merely appetitive ("brutish") state is a kind of destruction of the person.
The five senses and the sense organs — Aristotle first cataloged the five senses (sight, hearing, smell, taste, touch) and assigned each to its proper organ. Sensation is a change, a passage from potentiality to actuality.
Perception as dual actualization — In every act of perception two things are actualized: the sense organ comes to possess the sensible quality (the hand in snow becomes cold; the eye takes on the red of the tomato), and the object passes from being potentially perceived to actually perceived. The organ receives the sensible form without the matter.
The senses cannot lie — Senses merely transmit data; only judgments, made by the soul, can be true or false. The bent-looking stick in water and the "warm vs. cool" bucket are correct data misjudged, not deceptions — a direct rebuke to the Sophists' argument from illusion.
Quantitative vs. qualitative properties — Quantitative properties (length, mass — anything measurable in units) exist in reality; qualitative properties (color, warmth) exist only in the act of perceiving. A tomato is not red in itself but has the potentiality to be perceived as red — a potentiality fixed, not arbitrary, by its physical (quantitative) structure. We measure quantities only by reading off qualities.
Proper vs. common sensibles; the common sense — Some objects are proper to one sense (color to sight alone); others are common sensibles perceptible by several senses (motion, shape). The common (central) sense unifies the separate sensory streams into the perception of a single object — an apple seen, smelled, and felt as one thing.
Inner senses and the ladder to knowledge — Beyond the external senses lie memory, imagination, and mind. The cognitive ascent runs: sense data → (common sense) → perception → (passive intellect) → concept → (active intellect) → proposition → argument → science.
Passive and active intellect (nous) — The passive intellect receives forms, abstracting concepts from perceptions; it can become any form, so it must itself have no prior structure (see below). The active intellect constructs with those forms — building propositions, arguments, and sciences — and carries agency; it is the part Aristotle hints is immortal.
Thinking as receiving forms — As the sense organ takes on the sensible form, the intellect takes on the intelligible form of its object, minus the matter. His inverse analogy: in consumption you take in a carrot's matter and leave its form; in thought you take in its form and leave its matter. To be "informed" is literally to have taken form into the mind.
The blank passive intellect (anticipating Kant) — Because the passive intellect can know anything, it can carry no built-in structure; any prior "lens" (Kant's innate Euclidean geometry, say) would filter every judgment and cut our conclusions off from reality itself. Moreover such a view is self-undercutting: if the mind's structure forced the belief, one could never know the mind has that structure. So the passive intellect is pure receptivity, and the forms it takes in are forms of reality.

Worked Example

The faculties of soul as a strict inclusion chain. Aristotle's grades of soul are nested: each higher grade contains all the powers of the lower and adds its own, so possessing a higher soul presupposes the lower. Model the powers of each kind of soul as sets of faculties and make the nesting precise.

Name the faculty sets. Let the basic life-powers be $V = \{\text{nutrition},\ \text{growth},\ \text{reproduction}\},$ the added animal powers $S_{+} = \{\text{perception},\ \text{appetite},\ \text{locomotion}\},$ and the added human power $R_{+} = \{\text{reason}\}.$
Build each soul by accumulation. A plant's soul has only the nutritive powers; an animal's adds the sensitive powers; a human's adds reason: $V_{\text{plant}} = V, \qquad S_{\text{animal}} = V \cup S_{+}, \qquad R_{\text{human}} = V \cup S_{+} \cup R_{+}.$
Read off the strict inclusions. Since $S_{+}\neq\varnothing$ and $R_{+}\neq\varnothing$ and none of these powers repeat across the added sets, $V_{\text{plant}} \subsetneq S_{\text{animal}} \subsetneq R_{\text{human}}.$ This is the hierarchy nutritive $\subset$ sensitive $\subset$ rational: plants have only the nutritive; animals add the sensitive/locomotive; humans add the rational.
State the presupposition principle. Each higher soul includes the lower, so having a faculty at one level guarantees every lower-level faculty. For any faculty $f$ , $f \in V \ \Rightarrow\ f \in S_{\text{animal}} \ \Rightarrow\ f \in R_{\text{human}},$ i.e. reason is never found without perception, and perception never without nutrition. The converse fails: nutrition occurs without perception (in plants), and perception without reason (in brutes).
Interpret the failures downward. Damaging a human's rational faculties without destroying the rest leaves $V \cup S_{+}$ — an animal-like ("brutish") existence; further reduction to $V$ alone is the merely vegetative state. Because each grade is an essential part, such a reduction is the destruction of the person as that kind of being.
Locate self-actualization at the top. A thing flourishes by exercising its highest faculty. For a human that faculty is the one in $R_{+}$ , reason, so the good human life is the exercise of reason — the bridge from the De Anima into the Ethics. $\blacksquare$

Summary

The soul is the form (first actuality) of a living body, not a spirit within it: organism = body (matter) + soul (life-principle), and the two cannot exist apart — Aristotle's rejection of Platonic dualism.
Soul faculties form a strict inclusion chain, nutritive $\subset$ sensitive $\subset$ rational: plants have only nutrition/growth/reproduction, animals add perception and self-motion, humans alone add reason, and each higher grade presupposes the lower.
Perception is a dual actualization in which the sense organ takes on the sensible form without the matter; the senses only supply data and so cannot lie — error lies in judgment, not sensation.
Quantitative properties are real while qualitative ones (color, warmth) arise only in perceiving; the common sense binds the separate sensory streams into unified perceptions, from which the intellect abstracts concepts.
The intellect (nous) splits into a passive part that receives forms — and therefore can have no prior structure, an argument that pre-answers Kant — and an active part that constructs propositions, arguments, and sciences, and which Aristotle obscurely suggests is the immortal element.