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Dictionary of the History of Ideas

Studies of Selected Pivotal Ideas

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Psychology is a modern term, but its components,
psyche and logos, are words whose history goes back
to the Indo-European parent language. For the philos-
ophers of classical antiquity, giving an “account”
(logos) of the psyche was a necessary part of intellectual
inquiry. Greek philosophy was vitally concerned with
many of the problems which exercise modern
psychologists, but did not regard “study of the mind”
as an autonomous subject with specific terms of refer-
ence. Frequently theories about the psyche were
intimately connected with ethical, physical, and meta-
physical assumptions.

In this article “antiquity” means the period of
Greco-Roman civilization (ca. 750 B.C.-A.D. 450), and
“psychological doctrines” means theories held about
the psyche by philosophers. It is necessary to leave the
term psyche untranslated initially, since it cannot be
accurately rendered by a single English word such as
“soul” or “mind.” The meaning of psyche will best
appear by examining its functions and what it is used
to denote. Most of this survey is devoted to a chrono-
logical discussion of the major psychological doctrines,
but a preliminary note on the language and popular
conceptions inherited by philosophers will help to set
the scene.


The Homeric poems (ca. 750-700 B.C.) are the earli-
est European literature. In them references to psyche
are almost confined to descriptions of death or the
dead. A man who has lost his psyche is either dead
or unconscious (through fainting) and it is probable that
the word has a primary association with breath. The
precise location of psyche in the body is obscure,
though there are good reasons for associating it with
the head (R. B. Onians, The Origins of European
Cambridge [1951], pp. 95-115). Psyche is
sufficiently corporeal to be “breathed out” through the
mouth or through a wound and to survive as a ghost
when it has left the body. But though essential to the
living man, psyche is not connected in Homer with
any particular activity. Nous is his favorite word to
describe “mental seeing” or “planning” and it can
sometimes be translated “mind.” To denote emotions
the important word is thumos (physically associated
with breath and blood). A man may “desire in his
thumos” or his thumos may “urge him to do some-
thing.” Though not regarded as “organs” of the body,
nous and thumos are permanent possessions of the
living man to which his thinking and feeling belong.
There are other words which overlap or go beyond
these, but Homer does not have a single noun to denote
the soul or personality. Nor does he use a single term
for “body.” When the Homeric hero is under emotional
stress he may externalize his heart or his thumos,
scolding it or conversing with it. The notion that emo-
tions or intellect are in some sense independent of their
possessor is illustrated by the “psychic intervention”
(Dodds [1951], pp. 5-16) seen in expressions like “Zeus
took away his understanding” or “A god put courage
into his heart.”

The survival of the psyche in Homer appears not
to possess any important ethical or religious associa-
tions. Deprived of the body, the psyche lives on in
Hades, a feeble transformation or residue of the living
man. Essentially, the man whose psyche has left the
body is dead. Merely to survive as a psyche did not
make him immortal (athanatos). For to be athanatos
(literally “deathless”) is to possess the property of the
gods, and the Homeric psyche is so far from being
divine that it is compared to smoke. The immortality
of the soul was a concept which Greeks as late as the
fifth century B.C. found surprising (Herodotus IV, 93ff.).

The significance of the development between
Homeric thought and early philosophy has been
admirably analyzed by Snell (Die Entdeckung des
pp. 12ff.); but a caveat is perhaps needed
against his claim that Homer gives a fully repre-
sentative picture of Greek ways of thinking at a par-
ticular time. Homer is the culmination of a long oral
tradition which has its own highly formalized expres-
sions. In the lyric poets of the next two centuries psyche
came to be treated as the seat of emotions, in spite
of its Homeric associations with death; and it is possible
that such a use of the word is not as novel as its absence
from Homer might suggest. Eventually intellectual
activity was also ascribed to psyche and by the fifth
century B.C. psyche has changed its relation to other
words and become the name for a single thing to which
consciousness and vitality in general belong. How and
why this happened is impossible to answer precisely,
but it is certain that religious conceptions associated
with the names of Orpheus and Pythagoras were highly

The essence of these conceptions, which probably
go back to the sixth century B.C. in northern Greece
and southern Italy, is as follows: the psyche is an im-
mortal (and therefore divine) being, sullied by incor-
poration into a mortal body but capable by initiation
and ritual observances of becoming pure and eventu-
ally free of its earthly shell. Rebirth in various forms
and final union with the universal divinity are essential
features of this doctrine. It is clear that the Homeric
concept of psyche has become quite transmuted here.


Now, far from signifying merely that which leaves a
man when he dies, psyche must, in order to fulfill the
religious belief, denote his living self or personality.
The full significance of this concept was to be devel-
oped by Plato, but some earlier philosophers (whether
or not they accepted the religious belief) now treated
psyche as the center of consciousness.


1. Thales and Anaximenes. The first Greek thinkers
who are conventionally called “philosophers” were
more interested in cosmogony and cosmology than in
the study of man. To Thales of Miletus psyche seems
to have denoted both life and the source of motion.
The concept of psyche as that which moves and ani-
mates the body is a natural development of the view
that a dead (motionless) body has lost its psyche. In
Aristotle's opinion (De anima 411a 7f.) Thales may
have believed the world itself to possess psyche; and
many later philosophers certainly took this view.
Anaximenes, Thales' younger fellow-countryman, drew
a specific analogy between the human psyche and the
material which he supposed to surround (and control)
the cosmos (frag. 2). Both were identified with breath
or air, and the point of the comparison is clearly that
the psyche in man possesses a function similar to that
of air in the world. Psyche or air is the life-principle.
Thales and Anaximenes did not apparently discuss
psychology in detail, but the assumption of an affinity
between the human psyche and the cosmic principle
belongs to the same climate of ideas which gave rise
to beliefs in the psyche as the divine element in man
and the center of his consciousness.

2. Heraclitus. In Heraclitus of Ephesus all these
concepts occur and they are also associated with an
interest in sense perception and theory of knowledge.
To Heraclitus the senses are the first source of informa-
tion about the world, but their witness can be mislead-
ing (frag. 107). If the evidence of the senses is correctly
interpreted by the soul (by which psyche will now be
translated) it can bring about an understanding of the
logos, the principle determining all things. This princi-
ple, which means the unity behind opposition and
change, is not directly an object of perception, though
Heraclitus may have supposed it to be “drawn in”
physically through the senses (Guthrie [1962], p. 430).
Logos is an object of intellectual apprehension which
a soul in the right condition can grasp. The principle
has as its material constituent fire, and Heraclitus
probably also regarded fire as the fundamental material
of soul, since “it is death to soul to become water”
(frag. 36), while “a dry [i.e., hot] soul is wisest and
best” (frag. 118). A number of fundamental ideas are
involved here. First, the soul is now treated as the
recipient of sense-impressions. Second, it is able, by
interpreting these, to grasp a principle which is not
strictly empirical. Third, the soul at its best is analogous
to, if not identical with, the fiery cosmic principle.
Aristotle, much later, was to talk of “the thought which
thinks itself,” and the embryo of this notion may be
contained in Heraclitus' belief that the soul is both the
apprehender of logos and in some sense identical with
logos. These ideas were not stated in such precise terms
by Heraclitus himself. Indeed he advised that the soul
possesses depths which cannot be grasped (frag. 45).
But they are reasonable inferences from his oracular
fragments. He probably believed that the soul was
immortal, and that excellence of character went along
with intellectual understanding. In this he anticipated
Plato, but also his near contemporary, Empedocles.

3. Empedocles. In Empedocles, science and mysti-
cism are curiously blended. But though it would be
improper to draw an absolute distinction between his
two poems, On Nature and Purifications, the former
is primarily an attempt to explain the physical world
and the latter an account, in the Orphic-Pythagorean
tradition, of the incarnations, rewards, and punishments
of the “soul” (daimon). Since the work On Nature
accounts for sense perception, emotion, and thought
in purely material terms, without reference to a psyche,
it is hard to know what role the immortal soul played
in the mortal body. Empedocles' account of this is
confined to the religious poem (in the evidence which
survives) and it is safest to assume that he distinguished
the source of physical consciousness from the moral,
immortal self. If so, Empedocles has come nearer to
the concept of a soul which is quite distinct from the

Empedocles gave detailed explanations of sense per-
ception and thought. It is difficult to summarize these,
since they are intimately connected with his basic
assumptions about the world. Four elements, earth, air,
fire, and water, and two polar forces, Love and Strife,
constitute all that exists. To perceive is to receive in
the pores of the sense organs effluences from the exter-
nal elements, which are recognized by similar elements
in the sense organs. Thought takes place primarily in
the blood, which is composed of a nearly perfect mix-
ture (frags. 98, 105) of the elements. It is by thought
that we perceive Love and Strife, which are probably
also embodied in the blood. Empedocles does not ex-
plain whether or how the evidence of the senses is
organized by thought. At about this time a Pythagorean
philosopher, Alcmaeon, had traced perception from the
senses to the brain, but Empedocles may have regarded
thought itself as a category of perception which has
as its function receiving through the pores and assimi-


lating different combinations of external elements.
Even the elements are in some sense “conscious,” and
all processes, including emotional and mental activi-
ties, are referred to their mixture and separation. The
naiveté of the theory should not obscure its achieve-
ments. Empedocles has focused attention on the mech-
anism of consciousness, and offered an explanation
consistent with his theories about the natural world.
Psychology is here related to physiology. The investi-
gation of physical phenomena has aroused interest in
the physical processes of sensation and thought.

4. Parmenides. Other pre-Socratic theories may be
discussed more briefly. To Parmenides, whose influence
on Empedocles and subsequent philosophy was pro-
found, the physical world possessed no reality; for it
contained no subject of which “exists” could always
be truly asserted. Parmenides was unable to satisfy the
claims of his logic by reference to changing phenomena
and he rejected the senses in favor of nous, the mind
or the application of thought: the only existent is an
object of intellectual apprehension. For the history of
psychology this is important. Parmenides set up the
intellect as an autonomous faculty, quite independent
of sense perception. Its physical basis (frag. 16) is
obscure and hardly relevant to his main argument. But
among philosophers like Plato and Aristotle, who were
concerned with the relation between soul and body,
an analogous belief in the primacy and independence
of the intellectual faculty persists.

5. Anaxagoras and Democritus. It is improbable
that any pre-Socratic philosopher regarded mind or
soul as wholly immaterial. Anaxagoras made nous the
first cause of the cosmos and the controlling principle
of living things. He called it the “finest and purest of
all things” (frag. 12), which suggests that he was
coming close to expressing its immateriality. Unlike
Empedocles, Anaxagoras regarded perception as the
interaction of contraries; we recognize external heat
by virtue of cold in ourselves. He was also an extreme
realist, taking all qualitative differences to be funda-
mental differences in matter itself. This theory was
opposed by his contemporary, Democritus the atomist,
who referred all the qualities we perceive to changing
states of the body and its interaction with atoms of
different shapes. Democritus was consistent with the
general pre-Socratic position in giving the soul
(spherical atoms distributed over the body) the same
substance as his cosmic principle.


Plato's psychological theory is fundamental to his
whole philosophy and only its more striking aspects
can be indicated here. In regarding “cultivation of the
soul” as the primary duty, Plato was certainly influ
enced by Socrates and the Pythagoreans. Our knowl-
edge of Socrates is largely based on the works of Plato,
but it can be assumed that Socrates advocated and
practiced rigorous discussion about moral concepts as
the means of tending the soul and making it competent
to control the body and its passions. “Soul” here means
intellectual and moral self. The two attributes go hand
in hand. For it is only when we know what goodness
is that we can (and will) become good.

Dualism. Plato presents this intellectualist position
most strongly in the Phaedo. Soul and body are alien
substances. It is the aim of the soul, which is simple
in essence and immortal, to rid itself of the body, for
while it is embodied the soul cannot attain perfect
knowledge. The only objects of knowledge are Forms—
unique, incomposite, immaterial entities of which the
particular objects of perception are only fleeting
replicas. During embodiment the soul can apprehend
the Forms only by thinking as far as possible inde-
pendently of the body. Soul is the thinking, rational
self in direct opposition to the passions, pleasures, and
sensations associated with the body. It is still part of
the soul's job to animate the body during its incarna-
tion, but this is a regrettable incursion on its spiritual
activity and Plato does not explain how the soul acts
on the body.

Differentiated Soul. This extreme dualism was not
Plato's final word. In the Republic (Book IV) soul loses
its unity and becomes divided into nous (“intellect”),
thumos (“passion”), and epithumia (“appetite”). To its
appetitive part are ascribed bodily desires; thumos is
the emotional element in virtue of which we feel anger,
fear, etc.; nous is (or should be) the controlling part
which subjugates the appetites with the help of thumos.
Plato seeks justification for this theory on two counts.
First, his quest for justice is based on the assumption
that the state is a large-scale analogue of the individual,
and therefore the components which sanction the
state's division into three classes (artisans, soldiers, and
guardians) are established as categories for analyzing
the psychology of the individual. Second, Plato invokes
the empirical fact of conflict within the individual
(Republic IV, 436ff.). At one and the same time we
may both desire to drink and be unwilling to drink.
But the same thing cannot act in opposite ways with
the same part of itself towards the same object at the
same time. If such conflict is to be referred to the soul
as a whole, then the soul must possess different parts
to account for the clash. It is also the case that passion
and appetite may conflict, for a man may be angry
with that in himself which prompts him to do some-
thing shameful. Hence a part of the soul different from
reason and appetite is required. Like the soldiers of
the ideal state, passion should be the ally of the


governing component. The basic conflict for Plato is
still between bodily desires and intellect, between sense
and reason, but the dualism of the Phaedo has been
modified by locating the division which follows from
incarnation within the soul itself. At the same time
Plato saw the possibility of reconciliation within the
divided self, for he asserts that the two lower parts
have “following reason” as their function (Republic IX,
586e). The true philosopher is one in whom the rule
of reason is established, and in this situation all parts
of the soul conspire together for a united good. Nor
is the rule of reason an exercise of cold intellection.
The rational part of the soul is a lover of wisdom, and
distinguished from the appetitive part not by the ab-
sence of all desire but by having a different object of
desire: the absolute, intelligible good.

This doctrine is presented mythically in the Phaedrus
(246a ff.), where the human soul is pictured as a
charioteer (reason) driving a pair of horses (passion and
appetite). The passionate horse is a clean, upstanding
creature which follows the guide of reason, whereas
its fellow horse is a shaggy, recalcitrant beast which
tries to drag the chariot down from its heavenly course.
Here the soul's composite nature does not depend on
incarnation; but the point of the image is the imperfect
human soul's moral tension, not its multiplicity of
function. Plato's division of the soul persists in later
works such as the Timaeus, in which the rational part
of the soul is stated to be divine and immortal, and
is contrasted with two mortal, irrational parts: passion
and appetite (69d ff.). The rational part is located in
the head and is composed of immaterial ingredients
blended from the basic principles of the intelligible
world and the world of physical change. The irrational
parts are located in the chest (passion) and the belly
(appetite). Their activities are associated with the
bodily organs which house them. The blood vessels
seem to be the instruments by which the different parts
of the soul communicate with each other.

Knowledge and Perception. Soul is self-moving, the
principle of motion (i.e., animation) both in individual
living things and in the world itself (Phaedrus 245c ff.).
The world is an intelligent, living creature on which
man himself is modelled. In its original, discarnate state
the human soul has direct acquaintance with the Forms
and thus acquires knowledge. This knowledge is for-
gotten when the soul enters a body but it can be
recalled, at least in part, by “dialectic,” rigorous philo-
sophical discussion, and the judgments which we make
about our perceptions presuppose it. All judgments
entail the use of such terms as “exists,” “is the same
as,” “is different from,” and these are not objects of
perception (Theaetetus 185a ff.). Learning is a process
of recollecting a priori truths, a doctrine Plato attempts
to prove in the Meno (81e ff.) by an experiment in
which an uneducated slave is shown how to “recall”
the answer to the problem, what square has twice the
area of that of a given square, by answering a series
of simple questions. Since sensible objects lack the
unchanging existence required by Plato of what is fully
real, he took less interest in the analysis of sensation.
But in later dialogues the soul is more explicitly related
to the body insofar as sensations are described as
movements, caused by external phenomena, which are
transmitted to the soul through the body (Timaeus 43c);
and pleasures which have their source in the body
penetrate to the soul (Republic 457c). Plato also recog-
nized a form of “judgment” in which the mind pro-
nounces rightly or wrongly on what is presented to the
senses (Sophist 263d-264b).

Plato's psychology is not a systematic doctrine,
rigidly adhered to. His view of the soul developed from
the uncompromising dualism of the Phaedo to a posi-
tion in which a unitary self is attainable if harmony
can be established between reason, emotion, and bodily
appetite. Body and mind are related to each other
through pleasure and sensation. But Plato never aban-
doned his belief in the priority of reason, the part of
man which is akin to the fully real, unchanging world
and which has as its essential function apprehending
that world.


With Aristotle, psychology became a subject of sys-
tematic inquiry. He devoted a whole treatise (De
) to defining soul and its functions, and a group
of smaller works (Parva naturalia) covers specific topics
such as memory and sleep. Aristotle regarded psychol-
ogy as an aspect of physical science, and his own
analysis is based on the principles which he lays down
for all study of the natural world. But the De anima
occupies a fundamental place in his entire philosophy.
The biological works require constant reference to it,
and it is highly relevant to the ethics, epistemology,
and metaphysics. Aristotle has good claims to be the
founder of “psychology,” though the word itself is not
used by him. All later Greek psychological theory
shows his influence, in both terminology and method.

Soul as Vital Principle. Aristotle began his career
as a student of Plato, and in his earliest works, of which
only fragments survive, he argued for the preexistence
and survival of the whole soul. According to that theory
the relationship of body to soul is temporary and con-
tingent. But in the De anima, a work of his later years,
Aristotle takes body and soul to be two aspects, which
are only conceptually distinguishable, of a single sub-
stance: “a body which possesses life” (II, 1). Aristotle
calls these two aspects “matter” and “form.” Soul is


the form which animate matter must possess. The
physical matter of an animal is not its soul, for what
distinguishes animate from inanimate is not physical
matter but “the possession of life.” The potentiality
to be alive is a natural property of certain bodies, and
it is in virtue of soul that such bodies realize this

Aristotle defines soul as “the primary actuality of
a natural body which potentially has life” (De anima
412a 27-28). By “primary actuality” he means the
actual possession of the faculties which are necessary
to life, just as an eye, in order to be an eye, must possess
the faculty of vision. It is clear that with this concep-
tion body and soul are necessarily related. Aristotle
recognizes that emotions, desire, perception—all func-
tions of the soul—are dependent on the body which
contains them. But the influence of Plato remains
strong enough to make Aristotle regard mind (nous)
as a faculty of soul which has no physical base and
which may be capable of existing apart from the body.
Of this more below.

Faculties of Soul. In the first book of De anima,
Aristotle surveys and criticizes earlier theories of the
soul. From them he draws certain general assumptions;
in particular, the soul is the principle responsible for
thought, sensation and perception (Aristotle's single
word aisthesis covers both), and movement. His
detailed analysis in the next two books is concerned
with these functions of soul.

Since soul is that which distinguishes animate from
inanimate, Aristotle considers what characteristics are
peculiar to living creatures. He nominates four: nutri-
tion (the faculty of growth and reproduction); sensa-
tion; locomotion; and thought. The first of these is a
“form of movement,” and it is possessed by every living
creature from plants upwards. Only man has all four
faculties, which thus serve as a way of classifying all
living things in ascending order of complexity.

This method of analyzing soul is an important ad-
vance on Plato's. Aristotle is not dividing the soul into
parts (a procedure which he opposes) but analyzing
its different functions. Possessing aisthesis means
possessing at least one (touch) of the five senses, and
it also entails imagination, pleasure and pain, and de-
sire. The latter is not a base part of the soul, but a
necessary concomitant of perception and sensation.
Aristotle in some sense is a behaviorist. He wants to
know how and why living creatures act, and he
analyzes this in terms roughly comparable to stimulus
and response. Thus an animal moves in space because
its appetitive faculty is prompted by an object which
presents itself as desirable (or good), and the animal
is then moved to pursue it (De anima III, 432b 15-17;
433a 27-29). In man the psychology of action is more
complex, since mind and desire may clash; but there
is no question of man's acting independently of desire
since all action is prompted by the good, as the agent
sees it. What man can do, if he has himself under
control, is to contemplate objects of desire or aversion
without acting in consequence, though physical
changes, such as rapid heartbeat, may ensue (De anima
432b 27-32). He also has the unique capacity to
deliberate and thus establish a goal of action inde-
pendent of his immediate environment and physical

Sensation and Perception. Aristotle devoted consid-
erable attention to the analysis of sensation and per-
ception (De anima II, 5-12). His theories here, though
hampered by inadequate physiology (the nervous sys-
tem, commonly confused with the arteries, was dis-
covered about sixty years after his death) represent a
major advance on previous speculation. Aristotle takes
sense perception to be an activity in which external
objects so act upon each sense organ that it receives
their form (perceptible properties) independently of
the matter with which this form is associated in the
object itself. Just as wax can be imprinted with various
impressions, so the sense organ or sense can become
qualified as colored, resonant, hot, etc. Neither the
sense nor its (perceptible) object has any actual exist-
ence except in the act of perception, and this takes
place when the appropriate medium (e.g., light in the
case of vision) is acted upon by the external object and
passes on its perceptible properties to the sense organ.
It has been observed that an explanation of aisthesis
as a “process of being acted on” does not square well
with the active notion of “discrimination,” which
Aristotle also attributes to this faculty (Hamlyn,
Classical Quarterly, 9 [1959], 12f.). Part of the difficulty
arises from a lack of terms to distinguish sensation from
perception. But Aristotle was not perhaps so confused
as some make out. The organ is so constituted that
it reacts in certain ways to the objects which fall
between the ranges, light-dark, soft-hard, etc. (De
423b 30-424a 10). The sense is a “mean” be-
tween two extremes and it is in virtue of this mean
that we are made aware of (or judge) the different
properties of objects. Hence the reason, according to
Aristotle, why we are not aware of temperature equiv-
alent to that of our own body.

A more serious difficulty is how to explain the coor-
dination of information received by the senses and the
problem of self-consciousness. Aristotle asserts that
each sense has its own object, to which it is necessarily
related. (He seems to exclude the possibility of halluci-
nation by connecting actual hearing with actual
sounding, De anima 425b 26ff.). But there are certain
properties such as motion, rest, shape, magnitude, and


number which are apprehended by more than one
sense. Since there is no sixth sense, this “perception
of common sensibles” is due to the cooperative activity
of the special senses, i.e., the whole faculty, and
Aristotle calls this “common sense” (De anima 425a
14-425b 11). Whereas we can never, in Aristotle's
view, be deceived by the simple qualities (e.g., color,
sound) reported by the special senses, we can make
mistakes about the common sensibles; we can also
relate any object of perception to the wrong external
object (what Aristotle calls the “incidental” object of
perception), i.e., take what we perceive to be Socrates
when it is Plato. For perception does not tell us what
something is (this is the job of the mind); it gives
information about the qualities of an object. The pre-
cise workings of “common sense” are obscure in the
De anima. In the Parva naturalia mention is made
of a single, unified sense faculty, probably located in
the heart, by which the data of sense are coordinated
and on which self-awareness, imagination, and dream-
ing depend. But if Aristotle envisaged such a role for
“common sense” in the De anima he does not say so.

Thought. Artistotle's account of thought is obscure
and unsatisfactory. Much of the difficulty derives from
the fact that he takes thought to be an activity
analogous to aisthesis, i.e., a change brought about by
an object, in this case “thinkables” or “intelligibles”
(De anima III, 4). Now in sensation the sense organ
is acted upon by external phenomena, but these are
not available to actualize the mind, which “has no
organ.” Aristotle takes the mind to be in one respect
analogous to a blank wax-tablet on which anything can
be imprinted; in this sense mind is capable of receiving
and becoming identical with any object of thought,
but it has no actual existence until it thinks. In another
respect, the mind is an ever-active power that
actualizes its own capacity for thought in the manner
of light which makes potential colors actual (ibid., III,
5). This doctrine of an active intellect is necessary,
given Aristotle's theory of potentiality, if the capacity
of the passive intellect is to result in an actual cognitive
process. But the active intellect does not apparently
create its own objects of thought. Where then do they
come from? They cannot be independent substances,
like Plato's Forms. But thought is concerned with
“forms” or “essences”—what things really are—and it
thinks them with the help of mental images (ibid., 431a
14-15). Aristotle seems to conceive of imagination as
a faculty, intermediate between aisthesis and thought,
which provides the mind with the data in which it
can conceptualize the essential form of particular
things, or, in the case of abstract thought, the form
of, say, triangle without reference to any actual existing
triangle. But the precise relationship between imagi
nation and the two aspects of mind is very uncertain.

In its active aspect mind is independent of body,
eternal and immortal. It is not engendered in the phys-
ical process of conception but enters the womb “from
outside.” But what kind of existence the individual
mind enjoys when separate from the body is not
explained. God, for Aristotle, is nothing but an ever-
active mind, and man has something of God present
in himself through his active intellect.

This doctrine does not seriously contradict Aristotle's
view of soul and body as two aspects of a single sub-
stance. Soul essentially is that which actualizes the
body's vital capacities, but the active intellect has no
physical correlate, though it temporarily unites with
the passive intellect, which ultimately seems to depend
on the body. The details of this theory are not
Aristotle's main concern in the De anima. There he
shows how the response of a living creature to its
environment can be analyzed as a movement, varying
in complexity from the single nutritive functions of a
plant to the behavior of man, who responds by his
rational and appetitive capacities to the data provided
by the senses and imagination. Knowledge is the
formulation of general notions by induction from the
particular objects of perception. This ability to frame
concepts provides man with his ethical goals and the
subject matter of his scientific inquiries.

Aristotle's psychology is a general analysis of the
determinate capacities of the species which fall under
the genus animal. It has important metaphysical and
ethical applications, but unlike Plato, Aristotle
emphasized the organic unity of body and soul, and
established terms of reference for investigating animal


1. Theophrastus and Strato. After Aristotle's death
the philosophical school (Lyceum or Peripatos) associ-
ated with his name won fame as a center of scientific
research, under its successive heads, Theophrastus and
Strato. Theophrastus' De sensu, a historical survey of
theories of sensation and perception, is an invaluable
source of information about the pre-Socratics, but the
little that is known about his own psychological theory
suggests that he followed Aristotle in most respects.
He did, however, raise questions about the “external”
origin of intellect and the manner of the association
between the active and passive intellect (Themistius,
In De an. 430a 25). In this context, and for what follows,
Strato is a figure of major importance, a fact which
has not always been fully appreciated. Evidence about
him is scanty, but it reveals a thinker of the highest
scientific quality. Strato departed radically from the
Platonic and Aristotelian tradition in regarding sensa-


tion, perception, emotion, and thought as multiple
aspects of a single, unified consciousness (Plutarch, De
libidine et aegritudine
697b). This he located in a
central organ (the front part of the brain) which com-
municates with the sense organs and the rest of the
body via pneuma (“fine air or breath”). Sensations
occur not in the organs themselves but in this
sensorium, whence they are projected to the particular
part of the body which is affected (Aëtius, IV 23, 3).
Strato thus provided a firm physiological basis for
consciousness lacking in Aristotle's system, and com-
pletely abandoned the distinction between rational and
irrational faculties, as well as the belief in an immortal
soul or a transcendent reason. Mind is not peculiar to
man; rather, it is a necessary condition of sensation
and perception, since the data of sense require “atten-
tion” if they are to be registered (Plutarch, De sollertia
961a). In this theory, thought is down-
graded to “consciousness,” a thoroughly heretical no-
tion in the general context of Greek philosophy. For
his physiology Strato was certainly influenced by med-
ical science which, probably shortly after his death,
was revolutionized by the discovery of the nervous
system. (See F. Solmsen, “Greek Philosophy and the
Discovery of Nerves,” Museum Helveticum, 18 [1961],
150-63, 169-97.) Strato's use of pneuma as the carrier
of “messages” (Aristotle in his biological works had
already assigned to pneuma the function of trans-
mitting bodily movement) as well as his concept of
a unified consciousness found further development in
the psychology of the Stoics.

2. Stoics and Epicureans. In spite of their scientific
achievements the Peripatetics were not the major
influence on later Greek thinking in its broader sense.
Epicurus and Zeno (of Citium), who founded schools
in Athens at the end of the fourth century B.C., inaugu-
rated two philosophical systems which rapidly acquired
rival adherents from a wider range of society than Plato
and Aristotle had affected. It is customary to invoke
the conquests of Alexander the Great and the collapse
of the Greek city-state in accounts of the origin of these
systems. The instability of the times and the inadequacy
of traditional ethics may well help to explain the suc-
cess and motivation of Epicurus and Zeno, who both
provided a morality which stressed the self-sufficiency
of the individual. But the intellectual basis of both
systems is thoroughly Greek and their psychological
theories develop ideas already discussed.

These theories may conveniently be studied in con-
cert, for Stoicism and Epicureanism possess striking
similarities as well as contrasts. Both systems are a form
of materialism: for Epicurus, following Democritus, all
that exists is atoms, differing in size, shape, and weight
(this last an innovation), which by deviating from their
normal downward movement in empty space collide
and form temporary compound bodies. In living things
the soul itself consists of very fine atoms, resembling
fiery air, which pervade the whole body. No body
which lacks a soul can be alive and soul cannot be
sentient or cause sensation unless it is housed in a body,
a doctrine which rules out the survival of consciousness
after death (Letter to Herodotus 63-64). The soul-atoms
located in the human breast constitute “mind,” which
controls and issues instructions to the rest of the soul
(Lucretius, III, 136-44). Mind and soul are thus in
permanent contact with all parts of the body. Sensation
is the result of eidōla (effluences exactly reproducing
external objects) striking the sense organs and thus
setting up a movement in the mind. And certain par-
ticularly fine “idols” (e.g., from the gods) penetrate
directly to the mind. All sensations as such are true,
and the only source of knowledge; but they may be
misinterpreted by the mind and hence errors arise.
General ideas are built up by the mind from repeated
presentations of the same object, and perception occurs
when individual presentations match the general idea.
Scientific thought seems to operate by the juxtaposition
of two sets of atoms within the mind, constituting
different concepts (C. Bailey, Epicurus [1926], p. 269),
but the evidence for this theory is notoriously obscure.

In Stoicism the soul also permeates the whole body
and finds its “thinking center” in the heart. It consists
not of atoms but pneuma (“fiery breath”) in a particular
state of “tension.” For the Stoics, all that exists consists
of bodies differentiated by pneuma, the active force
which binds the passive material qualities, earth and
water, into individual things according to its tension.
(Like the pre-Socratics, Stoics and Epicureans ex-
plained soul in terms of the basic principle governing
the universe.) Pneuma is not merely a mechanistic
concept, like the Epicurean atom, but a dynamic,
rational force which pervades and activates the whole
world, all parts of which are thus interconnected. In
perception the sense organs are acted upon by objects,
either directly or through a medium, and this sets up
a presentation (phantasia) which is reported to the
central organ by currents of pneuma. The agent has
the power to assent or not to the presentation, and
his act of assent constitutes perception or “grasping”
the object. The Stoics argued that presentations which
completely reproduce the object are grasped as true
by men of normal health, and on the basis of these,
general ideas are built up by analogy, combination,
etc. (Cicero, Academica posteriora I, 41-42; Sextus
Empiricus, Adversus mathematicos VII, 227-60;
Diogenes Laërtius, VII, 45-54). Presentations can also
occur without an external cause, a theory which ac-
counts, inter alia, for hallucination. Like the


Epicureans the Stoics based their theory of knowledge
entirely on perception.

Both systems gave special attention to motivation.
For the primary impulse the Stoics took “innate
attraction towards those things which are peculiarly
suited to preserve an animal's natural well-being and
avoidance of their opposites” (Cicero, De finibus III,
16ff.). All living creatures are endowed with a drive,
and this is naturally stimulated by awareness of the
appropriate object. Without this drive no action is
possible, and it follows on a mental picture stemming
from something internal or external. What distinguishes
man from other animals is the possession of reason.
This develops through childhood, and in maturity ena-
bles a man to control his drives and so make responses
to the environment which are rational and moral as
well as appropriate in the instinctive sense. Assent
plays its part here as a means of determining the mental
attitude, which is open to the individual's control.
From God's viewpoint all events are predetermined,
but so far as human action is concerned the causal
factor (as in Aristotle) is primarily the disposition which
the agent has acquired by repeatedly acting in a certain

The Stoics underrated emotions, which they
regarded as perverted judgments, except in the case
of the sage. Like Strato they unified all functions of
soul. For the Epicureans, by contrast, pleasure and
avoidance of pain are the primary impulse of living
creatures and the foundation of ethics. They constitute
the objects of desire by which all action is prompted
(Cicero, De finibus I, 29ff.). For any action to take
place, mental images in the form of “idols” must strike
the mind and obtain its attention. Then the will is
activated and movement transferred from the mind to
the limbs (Lucretius, II, 261-83). The freedom of the
will in action is explained by reference to an indeter-
minate “swerve” of atoms (Lucretius, II, 250-60). This
has generally been taken to imply a spontaneous
movement of soul atoms for every voluntary act. But
it has recently been argued that the swerve explains
not particular voluntary acts but merely the fact that
character is not wholly determined by antecedent
causes (D. J. Furley, Two Studies in the Greek Atomists,
Princeton [1967], pp. 169-237).

Stoicism and Epicureanism are primarily theories of
ethics, and their psychology focuses attention on the
motives and processes of human action. Both abandon
completely any idea of an incorporeal mind; mental
activity is psychosomatic activity in which the soul acts
by physical processes upon the body. Human behavior
is necessarily related to the environment, from which
all the data used to form concepts are derived. Such
materialism and behaviorism were completely
abandoned by the last great pagan and early Christian


Between the foundation of Stoicism and Epicurean-
ism and the establishment of Christianity as the official
religion of the Roman empire lies a span of some six
hundred years. The early part of this period produced
a ferment of ideas in philosophy and science. But the
first two hundred years of the Roman Empire, in spite
of the achievements of the anatomist Galen and the
astronomer Ptolemy, were not a time in which original
thought flourished. Much was done to synthesize, mod-
ify, or reinterpret existing theories, but the dominance
of Rome, so fruitful in many respects, was not con-
ducive to philosophical speculation. Yet there were
forces at work which were to produce figures of major
importance in the history of ideas, in particular Ploti-
nus and Augustine. In them classical philosophy and
the eclecticism of the age combined with spiritual
theology in a remarkable way.

1. Plotinus. As concern with moral conduct became
increasingly dominant among philosophers, so interest
became ever more centered on the “inner man.”
Already in Stoicism it was the attitude of mind, the
internal disposition, which mattered in ethical judg-
ment, but Stoicism remained earthbound by its denial
of any existence to the incorporeal. In Neo-Platonism,
as established by Plotinus, the highest human activity
is contemplation of the transcendent Good, which is
the source of various grades of being. Lowest on the
scale is the material universe, including the human
body with which the soul forms a mysterious and
temporary union. This looks similar to Platonic
dualism, but in fact it is significantly different. For
Plato embodiment prevents the soul from fully grasp-
ing the Forms. But for Plotinus the body is not a
necessary barrier to union with the One or ultimate
Good, the goal of human endeavor. This follows be-
cause man's soul in its highest aspect is continually
engaged in intellection of the Forms; it is “illumined”
by Intellect, the principle second only to the One or
Good. In this activity the soul is not self-conscious,
since this would detract from its attention to the object
of contemplation. Plotinus notes that certain activities,
such as reading, go better if we are unconscious of
ourselves as acting. What “comes down” to the mate-
rial world and joins with body is an irradiation from
the higher soul. But this lower soul is incorporeal, and
Plotinus discusses the problem of its relation to the
body at length (Enneads I, 1, 1-10; IV, 3, 9-23). He
rejects all previous explanations of this relationship in
favor of an analogy with light: soul is present to body


as light to air. The living body is “illumined” by soul.
In sensation the soul uses the body and reads impres-
sions made on it. Hence there is no action of body
on soul. The two remain “separate but in contact.”
Memory and perception both belong to soul and
depend on its faculty of imaging (Enneads IV, 3, 27).
The soul sees when it looks out at externals. In thought
the faculty of imaging is acted upon by the higher soul,
and this provides the principles with which reason
works. Memory is a concept of great importance for
Plotinus because it provides (or is) the continuity of
self-consciousness. Only by memory does the embodied
soul possess an image of itself. It is through desire for
the lower that soul enters into body, and it is by desire
for the higher that the soul can recall memory of its
activity in the intellectual sphere and aspire eventually
to forget all the lower (including self-awareness) in
contemplation of the divine.

2. Augustine. Plotinus was the last great pagan
philosopher of classical antiquity, but it is no coinci-
dence that he shares much with Saint Augustine. In
interpreting the scriptures Augustine was influenced
by an intellectual climate common to pagan and
Christian; and inner experience as revealed by intro-
spection becomes the key to psychology. In a summary
it is impossible to do more than indicate some of
Augustine's major doctrines on the soul. In the De
quantitate animae
problems of the soul's relation to
the body, and the nature of sensation and thought are
discussed in dialogue form. The soul is incorporeal and
its substance cannot be named; rather must it be
inferred from the fact that God, its creator, is its proper
habitation (Patrologia Latina, 32, 1036). The soul shares
in reason and is fitted to rule the body. By its presence
it vitalizes the body and forms this into a harmonious
unity. In this doctrine Augustine is closer to Plotinus
than to Aristotle. The soul can take note of the body's
changes (and this is Augustine's definition of sensus)
but these do not affect the soul itself. In man the soul
possesses various grades of being (ibid., 1074ff.), a
ranking determined by the objects of its attention.
Apprehension of any kind is a result of the mind's
choosing to attend to something in its field of internal
vision. God is always present to the mind (whatever
its activity) and by His grace the souls of the faithful
at their highest possess a stable vision of the truth. It
is by divine illumination that the soul has standards
of judgment “impressed” on it, for the divine mind
contains eternal truths (P.L. 42, 1052). Like Plotinus
Augustine laid great weight on “memory,” for this is
not mere reminiscence but the storehouse of experience
and the mind's knowledge of itself (ibid., 1048). In
conversion the mind “remembers” God.

Augustine, for all his indebtedness to Greek thought,
looks forward to the Middle Ages. But it is not the
business of this article to chart the subsequent history
of psychology. Needless to say, modern thinking owes
more than is sometimes acknowledged to ancient psy-
chology. Between the materialism of Democritus and
the extreme spirituality of Plotinus runs a line on which
intermediate positions are taken by Descartes as well
as Plato, by Gilbert Ryle as well as Aristotle. In spite
of inadequate technical knowledge the Greeks devel-
oped ways of analyzing mind and body and the re-
sponse of an organism to its environment which con-
tinue to shape much of our thinking. They knew no
“science” of psychology, and were not hampered by
having to confine their attention to a neatly labeled
set of “mental phenomena.”


For pre-philosophical psychology the best starting points
are Erwin Rhode, Psyche: Seelenkult und Unsterblichkeits-
glaube der Griechen,
4th ed. (Tübingen, 1970; Engl. trans.
London, 1925); Bruno Snell, Die Entdeckung des Geistes,
3rd ed. (Hamburg, 1955), trans. as The Discovery of the
(Cambridge, Mass., 1953); E. R. Dodds, The Greeks
and the Irrational
(Berkeley, 1951). Texts of the pre-Socratics
are collected in H. Diels and W. Kranz, Die Fragmente der
6th ed. (Berlin, 1951-52). For an extended
treatment see J. I. Beare, Greek Theories of Elementary
(Oxford, 1906). W. K. C. Guthrie, A History of
Greek Philosophy,
Vols. I, II (Cambridge, 1962, 1965) has
extensive notes and bibliography. For Plato the most im-
portant texts are Phaedo, Phaedrus, Philebus, Republic IV-
VII, X; Theaetetus, Timaeus. For bibliography see H.
Cherniss, Lustrum (1961), 340-82, and for recent discussion
I. M. Crombie, An Examination of Plato's Doctrines, Vol.
I (London, 1962). Aristotle's psychological theory is set out
in De anima, ed. Hicks (Cambridge, 1907) and Parva
ed. W. D. Ross (Oxford, 1955); general discussion
and bibliography in I. Düring, Aristotles (Heidelberg, 1966).
See also D. W. Hamlyn, De anima Books II and III, with
Certain Passages from Book I
(Oxford and New York, 1968).
Some basic texts for post-Aristotelian psychology are col-
lected by C. J. de Vogel, Greek Philosophy. A Collection
of Texts with Notes and Explanations,
Vol. III (Leiden, 1959).
Relevant works of Augustine are De trinitate, De liberio
arbitrio, De quantitate animae,
and of Plotinus, Enneads I,
1; IV. This period is well surveyed by E. Zeller, Die Philos-
ophie der Griechen,
Vol. III, 1, 5th. ed. by E. Wellmann
(Leipzig, 1923), and A. H. Armstrong, ed., Cambridge History
of Later Greek and Early Medieval Philosophy


[See also Analogy in Early Greek Thought; Atomism;
Behaviorism; Biological Conceptions in Antiquity; Cosmol-
ogy; Dualism; Epicureanism; Imprinting; Neo-Platonism;
Platonism; Pythagorean...; Rationality; Stoicism.]