Aristotle’s Psychology

Aristotle (384–322 BC) was born in Macedon, in what is now northern
Greece, but spent most of his adult life in Athens. His life in Athens
divides into two periods, first as a member of Plato’s Academy
(367–347) and later as director of his own school, the Lyceum
(334–323). The intervening years were spent mainly in Assos and Lesbos,
and briefly back in Macedon. His years away from Athens were
predominantly taken up with biological research and writing. Judged on
the basis of their content, Aristotle’s most important psychological
writings probably belong to his second residence in Athens, and so to
his most mature period. His principal work in psychology, De
Anima, reflects in different ways his pervasive interest in
biological taxonomy and his most sophisticated physical and
metaphysical theory.

Because of the long tradition of exposition which has developed
around Aristotle’s De Anima, the interpretation of even its
most central theses is sometimes disputed. Moreover, because of its
evident affinities with some prominent approaches in contemporary
philosophy of mind, Aristotle’s psychology has received renewed
interest and has incited intense interpretative dispute in recent
decades. Consequently, this entry proceeds on two levels. The main
article recounts the principal and distinctive claims of Aristotle’s
psychology, avoiding so far as possible exegetical controversy and
critical commentary. At the end of appropriate sections of the main
article, readers are invited to explore problematic or advanced
features of Aristotle’s theories by following the appropriate
links.

Aristotle investigates psychological phenomena primarily in De
Anima and a loosely related collection of short works called the
Parva Naturalia, whose most noteworthy pieces are De
Sensu and De Memoria. He also touches upon psychological
topics, often only incidentally, in his ethical, political, and
metaphysical treatises, as well as in his scientific writings,
especially De Motu Animalium. The works in the Parva
Naturalia are, in comparison with De Anima, empirically
oriented, investigating, as Aristotle says, “the phenomena common
to soul and body” (De Sensu 1, 436a6–8). This contrasts
with De Anima, which introduces as a question for
consideration “whether all affections are common to what has the
soul or whether there is some affection peculiar to the soul
itself” (De Anima i 1, 402a3–5). That is, in De
Anima Aristotle wants to know whether all psychological states are
also material states of the body. “This,” he remarks,
“it is necessary to grasp, but not easy” (De Anima
i 1, 402a5). In this way, De Anima proceeds at a higher level
of abstraction than the Parva Naturalia. It is generally more
theoretical, more self-conscious about method, and more alert to
general philosophical questions about perception, thinking, and
soul-body relations.

In both De Anima and the Parva Naturalia,
Aristotle assumes something which may strike some of his modern readers
as odd. He takes psychology to be the branch of science which
investigates the soul and its properties, but he thinks of the soul as
a general principle of life, with the result that Aristotle’s
psychology studies all living beings, and not merely those he regards
as having minds, human beings. So, in De Anima, he takes it as
his task to provide an account of the life activities of plants and
animals, along side those of humans (De Anima ii 11, 423a20–6,
cf. ii 1, 412a13; cf. De Generatione Animalium ii 3, 736b13;
De Partibus Animalium iv 5, 681a12). In comparison with the
modern discipline of Psychology, then, Aristotle’s psychology is broad
in scope. He even devotes attention to the question of the nature of
life itself, a subject which falls outside the purview of psychology in
most contemporary contexts. On Aristotle’s approach, psychology studies
the soul (psuchê in Greek, or anima in Latin);
so it naturally investigates all ensouled or animate beings.

There is, however, one telling point of contact between Aristotle’s
investigations into the soul and the contemporary discipline of
Psychology: in each case, different questions yield different
directions and methods of inquiry, with the result that it is sometimes
hard to appreciate how so many variegated enterprises, though conducted
under one and the same rubric, could really belong to any one
coordinated discipline. Someone studying methods of Freudian
psychoanalysis will not, after all, have any immediate overlap of
either interest or method with a brain physiologist or a behavioral
geneticist. In a similar way, Aristotle seems reluctant to regard an
inquiry into the soul as belonging exclusively to natural science,
which is for him the branch of theoretical science devoted to
investigating beings capable of undergoing change. (He contrasts
“physics”, that is, natural science, with both mathematics and “first
philosophy” along these lines; Meta. vi 1 1025b27–30, 1026a18;
xi 7 1064a16–19, b1–3.) On the one hand, he insists that because
various psychological states, including anger, joy, courage, pity,
loving, and hating, all involve the body in central and obvious ways,
the study of soul “is already in the province of the natural scientist”
(De Anima i 1 403a16–28). At the same time, however, he
insists that the mind or intellect (nous) may not be enmeshed
in the body in the same way as these sorts of states, and so denies
that the study of soul falls in its entirety to the natural scientist
(Meta. vi 1 1026a4–6; De Partibus Animalium i 1
645a33-b10). This is presumably why in the opening chapter of De
Anima Aristotle reports a deep and authentic perplexity about the
best method for investigating psychological matters (De Anima
i 1 402a16–22). If different sciences employ different methods and the
study of soul is bifurcated so that it belongs to no one science, there
will indeed be a genuine difficulty about how best to proceed in any
inquiry concerning it. It seems fair to say that these sorts of
quandaries have not left us altogether. Although purely naturalistic
approaches to philosophy of mind have found staunch champions in
contemporary times, it would nevertheless be safe to say that much of
the discipline continues to employ traditional a priori
methods; some branches of cognitive science seem an admixture of both.
In any case, in view of the difficulties concerning the soul he
enumerates, Aristotle evinces an appropriate modesty when undertaking
its investigation: “Grasping anything trustworthy concerning the soul
is completely and in every way among the most difficult of affairs”
(De Anima i 1 402a10–11).

In De Anima, Aristotle makes extensive use of technical
terminology introduced and explained elsewhere in his writings. He
claims, for example, using vocabulary derived from his physical and
metaphysical theories, that the soul is a “first actuality of a
natural organic body” (De Anima ii 1, 412b5–6), that it
is a “substance as form of a natural body which has life in
potentiality” (De Anima ii 1, 412a20–1) and, similarly,
that it “is a first actuality of a natural body which has life in
potentiality” (De Anima ii 1, 412a27–8), all claims
which apply to plants, animals and humans alike.

In characterizing the soul and body in these ways, Aristotle applies
concepts drawn from his broader hylomorphism, a conceptual
framework which underlies virtually all of his mature theorizing. It is
accordingly necessary to begin with a brief overview of that framework.
Thereafter it will be possible to recount Aristotle’s general approach
to soul-body relations, and then, finally, to consider his analyses of
the individual faculties of soul.

‘Hylomorphism’ is simply a compound word composed of the
Greek terms for matter (hulê) and form or shape
(morphê); thus one could equally describe Aristotle’s
view of body and soul as an instance of his
“matter-formism.” That is, when he introduces the soul as
the form of the body, which in turn is said to be the
matter of the soul, Aristotle treats soul-body relations as a
special case of a more general relationship which obtains between the
components of all generated compounds, natural or artifactual.

The notions of form and matter are themselves, however, developed
within the context of a general theory of causation and explanation
which appears in one guise or another in all of Aristotle’s mature
works. According to this theory, when we wish to explain what there is
to know, for example, about a bronze statue, a complete account
necessarily alludes to at least the following four factors: the
statue’s matter, its form or structure, the agent responsible for that
matter manifesting its form or structure, and the purpose for which the
matter was made to realize that form or structure. These four factors
he terms the four causes (aitiai):

The material cause: that from which something
is generated and out of which it is made, e.g. the bronze of a
statue.

The formal cause: the structure which the
matter realizes and in terms of which the matter comes to be something
determinate, e.g., the Hermes shape in virtue of which this quantity of
bronze is said to be a statue of Hermes.

The efficient cause: the agent responsible
for a quantity of matter’s coming to be informed, e.g. the sculptor who
shaped the quantity of bronze into its current Hermes shape.

The final cause: the purpose or goal of the
compound of form and matter, e.g. the statue was created for the
purpose of honoring Hermes.

For a broad range of cases, Aristotle implicitly makes twin claims
about these four causes: (i) a complete explanation requires reference
to all four; and (ii) once such reference is made, no further
explanation is required. Thus, when appropriate, appeal to the four
causes is both necessary and sufficient for completeness and adequacy
in explanation. Although not all things which admit of explanation have
all four causes, e.g., geometrical figures are not efficiently caused,
even a brief overview of his psychological writings reveals that
Aristotle regards all four causes as in play in the explanation of
living beings. A monkey, for example, has matter, its body; form, its
soul; an efficient cause, its parent; and a final cause, its function.
Moreover, he holds that the form is the actuality of the body
which is its matter: an indeterminate lump of bronze becomes a statue
only when it realizes some particular statue-shape. So, Aristotle
suggests, matter is potentially some F until it
acquires an actualizing form, when it becomes actually F.
Given his overarching explanatory schema, it is hardly surprising that
Aristotle should advance a hylomorphic account of soul and body; this
is, for him, standard explanatory procedure.

Still, it is noteworthy that this four-causal framework of
explanation was developed initially in response to some puzzles about
change and generation. Aristotle argues with some justification that
all change and generation require the existence of something complex:
when a statue comes to be from a lump of bronze, there is some
continuing subject, the bronze, and something it comes to acquire, its
new form. Thus the statue is, and must be, a certain kind of compound,
one of form and matter. Without this type of complexity, generation
would be impossible; since generation in fact occurs, form and matter
must be genuine features of generated compounds. Similarly, but less
obviously, qualitative change requires much the same apparatus: when a
statue is painted, there is some continuing subject, the statue, and a
new feature acquired, its new color. Here too there is complexity, and
complexity which is readily articulated in terms of form and matter,
but now of form which is evidently inessential to the continued
existence of the entity whose form it is. The statue continues to
exist, but receives a form which is accidental to it; it might lose
that form without going out of existence. By contrast, should the
statue lose its essential form, as would happen for example if the
bronze which constitutes it were melted, divided, and recast as twelve
dozen letter openers, it would cease to exist altogether.

For the purposes of understanding Aristotle’s psychology, the origin
of Aristotle’s hylomorphism is significant for two reasons. First, from
its inception, Aristotle’s hylomorphism exploits two distinct but
related notions of form, one of which is essential to the compound
whose form it is, and the other of which is accidental to its subject.
In advancing his view of the soul and its capacities, Aristotle employs
both of these notions: the soul is an essential form, whereas
perception involves the acquisition of accidental forms. Second,
because Aristotle’s hylomorphism was initially developed to handle
puzzles of change and generation, its deployment in philosophical
psychology is sometimes strained, insofar as Aristotle is not
immediately willing to treat every instance of perception and thought
as a straightforward instance of change in some continuing subject.
Moreover, as we shall see, it is sometimes difficult to appreciate how
Aristotle can justifiably regard the body as the matter of a human
being in the way that the bronze is held to be the matter of a statue.
Bronze can exist as an indeterminate lump, being potentially but not
actually the statue of a great hero. There is no ready analogue in the
case of the body: the body is not so much stuff lying about waiting to
be enformed by a soul. Rather, in one important sense, human bodies
become human bodies by being ensouled. If so, then they seem
ill-suited to play the role of matter in precisely those terms given by
Aristotle’s hylomorphic theory of generation. (For further discussion
of this topic, after reading the next section, see
Supplement: A Fundamental Problem about Hylomorphism.)

In applying his general hylomorphism to soul-body relations,
Aristotle contends that the following general analogy obtains:

soul : body : : form : matter : : Hermes-shape : bronze

If the soul bears the same relation to the body which the shape of a
statue bears to its material basis, then we should expect some general
features to be common to both; and we should be able to draw some
immediate consequences regarding the relationship between soul and
body. To begin, some questions about the unity of soul and body, an
issue of concern to substance dualists and materialists alike, receive
a ready response. Materialists hold that all mental states are also
physical states; substance dualists deny this, because they hold that
the soul is a subject of mental states which can exist alone, when
separated from the body. In a certain way, the questions which give
rise to this dispute simply fall by the wayside. If we do not think
there is an interesting or important question concerning whether the
Hermes-shape and its material basis are one, we should not suppose
there is a special or pressing question about whether the soul and body
are one. So Aristotle contends: “It is not necessary to ask
whether soul and body are one, just as it is not necessary to ask
whether the wax and its shape are one, nor generally whether the matter
of each thing and that of which it is the matter are one. For even if
one and being are spoken of in several ways, what is properly so spoken
of is the actuality” (De Anima ii 1, 412b6–9). Aristotle
does not here eschew questions concerning the unity of soul and body as
meaningless; rather, he seems, in a deflationary vein, to suggest that
they are readily answered or somehow unimportant. If we do not spend
time worrying about whether the wax of a candle and its shape are one,
then we should not exercise ourselves over the question of whether the
soul and body are one. The effect, then, is to fit soul-body relations
into a larger hylomorphic pattern of explanation in terms of which
questions of unity do not normally arise.

It should be emphasized, however, that Aristotle does not here
decide the question by insisting that the soul and body are identical,
or even that they are one in some weaker sense; indeed, this is
something he evidently denies (De Anima ii 1, 412a17; ii 2,
414a1–20). Instead, just as one might well insist that the wax of a
candle and its shape are distinct, on the grounds that the wax could
easily exist when the particular shape is no more, or, less obviously,
that the particular shape could survive the replenishment of its
material basis, so one might equally deny that the soul and body are
identical. In a fairly direct way, though, the question of whether soul
and body are one loses its force when it is allowed that it contains no
implications beyond those we establish for any other hylomorphic
compound, including houses and other ordinary artifacts.

One way of appreciating this is to consider a second general moral
Aristotle derives from hylomorphism. This concerns the question of the
separability of the soul from the body, a possibility embraced by
substance dualists from the time of Plato onward. Aristotle’s
hylomorphism commends the following attitude: if we do not think that
the Hermes-shape persists after the bronze is melted and recast, we
should not think that the soul survives the demise of the body. So,
Aristotle claims, “It’s clear that the soul is not separable
from the body – or that certain parts of it, if it naturally has
parts, are not separable from the body” (De Anima ii 1,
413a3–5). So, unless we are prepared to treat forms in general
as capable of existing without their material bases, we should not be
inclined to treat souls as exceptional cases. Hylomorphism, by itself,
gives us no reason to treat souls as separable from bodies, even if we
think of them as distinct from their material bases. At the same time,
Aristotle does not appear to think that his hylomorphism somehow
refutes all possible forms of dualism. For he appends to his denial
of the soul’s separability the observation that some parts of
the soul may in the end be separable after all, since they are not the
actualities of any part of the body (De Anima ii 1,
413a6–7). Aristotle here prefigures his complex attitude toward
mind (nous), a faculty he repeatedly describes as exceptional
among capacities of the soul.

Still, in general, the soul is the form of the body in much the same
way the form of a house structures the bricks and mortar from which it
is built. When the bricks and mortar realize a certain shape, they
manifest the function definitive of houses, namely that of providing
shelter. Thus, the presence of the form makes those bricks and that
mortar a house, as opposed, e.g., to a wall or an oven. As we have
seen, Aristotle will say that the bricks and mortar, as matter, are
potentially a house, until they realize the form appropriate to houses,
in which case the form and matter together make an actual house. So, in
Aristotle’s terms, the form is the actuality of the house, since its
presence explains why this particular quantity of matter comes to be a
house as opposed to some other kind of artifact.

In the same way, then, the presence of the soul explains why this
matter is the matter of a human being, as opposed to some other kind of
thing. Now, this way of looking at soul-body relations as a special
case of form-matter relations treats reference to the soul as an
integral part of any complete explanation of a living being, of any
kind. To this degree, Aristotle thinks that Plato and other dualists
are right to stress the importance of the soul in explanations of
living beings. At the same time, he sees their commitment to the
separability of the soul from the body as unjustified merely by appeal
to formal causation: he will allow that the soul is distinct from the
body, and is indeed the actuality of the body, but he sees that these
concessions by themselves provide no grounds for supposing that the
soul can exist without the body. His hylomorphism, then, embraces
neither reductive materialism nor Platonic dualism. Instead, it seeks
to steer a middle course between these alternatives by pointing out,
implicitly, and rightly, that these are not exhaustive options.

Although willing to provide a common account of the soul in these
general terms, Aristotle devotes most of his energy in De
Anima to detailed investigations of the soul’s individual
capacities or faculties, which he first lists as nutrition,
perception, and mind, with perception receiving the lion’s share of
attention. He later also introduces desire, evidently as a discrete
faculty on par with those initially introduced. The broadest is
nutrition, which is shared by all natural living organisms; animals
have perception in addition; and among natural organisms humans alone
have mind. Aristotle maintains that various kinds of souls, nutritive,
perceptual, and intellectual, form a kind of hierarchy. Any creature
with reason will also have perception; any creature with perception
will also have the ability to take on nutrition and to reproduce; but
the converse does not hold. Thus, plants show up with only the
nutritive soul, animals have both perceptual and nutritive faculties,
and humans have all three. The reasons why this should be so are
broadly teleological. In brief, every living creature as such grows,
reaches maturity, and declines. Without a nutritive capacity, these
activities would be impossible (De Anima iii 12,
434a22–434b18; cf. De Partibus Animalium iv 10, 687a24–690a10;
Metaphysics xii 10, 1075a16–25). So, Aristotle concludes,
psychology must investigate not only perceiving and thinking, but also
nutrition.

There is some dispute about which of the psychic abilities mentioned
by Aristotle in De Anima qualify as full-fledged or autonomous
faculties. He evidently accepts the three already mentioned as
centrally important. Indeed, he is willing to demarcate a hierarchy of
life in terms of them. Even so, he also discusses two other capacities,
imagination (De Anima iii 3) and desire (De Anima iii
9 and 10), and appeals to them in both his account of thinking and his
philosophy of action. He does little, however, to characterize either
in any intrinsic way. He evidently regards imagination as a sort of
subordinate faculty, integrated in various ways with the faculties of
nutrition, perception, and thought. Desire is still more complex.
Despite its not occurring without the sensory faculty (De Anima
iii 7 412a12–14), desire seems in the end elevated to a full capacity,
primarily because of its role in the explanation of purposive behavior.
His discussions of imagination and desire raise interesting questions
about how Aristotle views the various capacities of soul as integrating
into unified forms. They also raise questions along with his
discussions of the other faculties as to how Aristotle conceives the
unity of the whole soul. Some scholars seem content to characterize an
Aristotelian soul as a set or sum of capacities, whereas Aristotle
himself evidently demands a non-aggregative form of unity (De
Anima ii 3 414b28–32, cf. iii 9 432a–b6).

When turning to these individual faculties of the soul, Aristotle
considers nutrition first, for two related reasons. The first is
straightforward: psychology considers all animate entities, and the
nutritive soul belongs to all naturally living things, since it is
“the first and most common capacity of soul, in virtue of which
life belongs to all living things” (De Anima ii 4,
415a24–25). The second is slightly more complex, being at root
teleological. Given that the higher forms of soul presuppose nutrition,
its explication is prior to them in the order of Aristotle’s
exposition.

Aristotle approaches his account of the nutritive soul by relying on
a methodological precept which informs much of his psychological
theorizing, namely that a capacity is individuated by its objects, so
that, e.g., perception is distinguished from mind by being arrayed
toward sensible qualities rather than intelligible forms (De
Anima ii 4, 415a20–21). This induces him to offer what may sound
initially like a pedestrian observation, that in nutrition there are
three components, “that which is nourished, that by which it is
nourished, and what nourishes (i.e. that which engages in
nutrition).” This, however, Aristotle unpacks by maintaining that
“what nourishes is the primary soul; what is nourished is the
body which has this soul; and that by which it is nourished is
nourishment (i.e. food)” (De Anima ii 4, 416b20–23). The
interest of this suggestion lies in the implication that all and only
living systems can be nourished, a consequence Aristotle makes more
explicit by claiming that “nothing is nourished which does not
have a share in life” (De Anima ii 4. 415b27–28) and
that “since nothing is nourished which does not partake of life,
what is nourished will be the ensouled body insofar as it is ensouled,
with the result that nourishment (i.e. food) is related to the
ensouled, and not coincidentally” (De Anima ii 4,
416b9–11). Here Aristotle means that food, as food, is definitionally
related to life. Whatever is food is already such as to be necessarily
related to living beings.

The significance of this observation resides in the thought that any
adequate account of nutrition will make ineliminable reference to life
as such. This in turn entails that it will not be possible to
define life as the capacity for taking on nutrition. For then
we would have a vicious circularity: a living system is the sort of
thing which can take on nutrition, while nutrition is whatever stuff is
such as to sustain a living system. So, if living systems cannot be
reductively defined in some other way, it will follow that no reductive
account of life will be forthcoming. Consequently, Aristotle’s
discussion of nutrition provides some reason for thinking that he will
resist any attempt to define life in terms which do not themselves
implicitly appeal to life itself. That is, he will resist any reductive
account of life.

This also seems to be the purport of Aristotle’s rejection of the
simple mechanistic accounts of growth which he considers when
discussing the nutritive soul (De Anima ii 4, 415b27–416a20;
cf. De Generatione et Corruptione i 5). Aristotle objects to
those who want to account for growth merely in terms of the natural
tendencies of material elements. For growth is a constrained
pattern of development, the source of which Aristotle ascribes to the
soul. He takes it as evident that growth in organisms proceeds along
structured paths, in end-directed ways. These structures in turn
manifest capacities whose explication cannot be given in crude
materialistic terms; for materialistic terms, as Aristotle understands
them, fail to account for the fact that mature members of species cease
growing, having realized the structures characteristic of their kind.
Fire, for example, by contrast “grows” haphazardly, without
directionality, flowing towards the combustible without end, until
hindered by external impediments or lack of fuel.

Now, the forms of materialist explanations Aristotle considers are
primitive. One critical question about his treatment of these
explanations concerns whether he is right to suggest that facts about
constrained patterns of development are incompatible with more
explanatorily advanced forms of materialism, and, if so, whether those
forms of materialism will be reductive in the sense that they will
avoid all implicit or explicit reference to life. So far, there is
little reason to think that Aristotle has been proven wrong; that is,
there is at present no reductive account of life which enjoys universal
or even broad support.

In any case, Aristotle’s discussion of nutrition is characteristic
of his general approach to the soul’s faculties. His discussions often
proceed on two levels. On the one hand, he simply seeks to provide an
account of the relevant phenomena. At the same time, his interests in
definition are conditioned by a host of broader methodological and
metaphysical concerns. Consequently, he attempts to capture the nature
of the individual faculties while at the same time investigating
whether reductive accounts of them are plausible. In this way, at
least, Aristotle’s investigations reflect sensitivity to an array of
interlocking questions in definitional methodology, including most
notably questions about the plausibility of reductive approaches to
life’s most characteristic features. These same interests are apparent
in his discussions of perception and mind.

Aristotle devotes a great deal of attention to perception,
discussing both the general faculty and the individual senses. In both
cases, his discussions are cast in hylomorphic terms. Perception is the
capacity of the soul which distinguishes animals from plants; indeed,
having a perceptive faculty is definitive of being an animal (De
Sensu 1, 436b10–12); every animal has at least touch, whereas most
have the other sensory modalities as well (De Anima ii 2
413b4–7). In broad terms at least, animals must have perception if they
are to live. So, Aristotle supposes, there are defensible teleological
grounds for treating animals as essentially capable of perceiving
(De Anima ii 3, 414b6–9, 434a30–b4; De Sensu 1,
436b16–17). If an animal is to grow to maturity and propagate, it must
be able to take in nourishment and to navigate its way through the
world. Perception serves these ends.

This much, however, does not explain how perception occurs.
Aristotle claims that perception is best understood on the model of
hylomorphic change generally: just as a house changes from blue to
white when acted upon by the agency of a painter applying paint, so
“perception comes about with <an organ’s> being changed and
affected … for it seems to be a kind of alteration”
(De Anima ii 5, 416b33–34). So in line with his general
account of alteration, Aristotle treats perception as a case of
interaction between two suitable agents: objects capable of acting and
capacities capable of being affected. That the agents and patients must
both be suitable is important, since we need to distinguish
between two ways, e.g., an odor might affect something. By being placed
in its vicinity, a clove of garlic might affect a block of tofu. The
tofu might well come to take on the odor of the garlic. But we would
not want to say that the tofu perceives the garlic. By contrast, when
an animal is affected by the same clove, it perceives the odor. Since
the garlic is the same in both cases, the difference in these cases
must reside in the character of the object affected. When animals
receive perceptual forms, perception results; when non-living entities
are affected by what seem to be the same forms, only non-perceptual
alteration occurs.

In both kinds of alterations, Aristotle is happy to speak of an
affected thing as receiving the form of the agent which affects it and
of the change consisting in the affected thing’s “becoming
like” the agent (De Anima ii 5, 418a3–6; ii 12,
424a17–21). So there is in both cases a hylomorphic model of alteration
involving enforming, that is, a model according to which
change is explained by the acquisition of a form by something capable
of receiving it. Consequently, whatever is changed in a given way is
necessarily such that it is capable of being changed in that way. This
is not the mere triviality that whatever becomes actually F
must already be possibly F. Instead, it is the recognition
that specific forms of change require suitable capacities in the
changing subjects, and that, consequently, analyses of specific forms
of change will necessarily involve consideration of those capacities.
No marshmallow can receive the form of an actual automobile; and only
entities capable of perceiving can receive the perceptible forms of
objects. This is Aristotle’s meaning when he claims: “the
perceptive faculty is in potentiality such as the object of perception
already is in actuality” and that when something is affected by
an object of perception, “it is made like it and is such as that
thing is” (De Anima ii 5, 418a3–6).

This hylomorphic restriction on the suitability of subjects of
change has the effect of limiting cases of actual perception to those
instances of form-reception which involve living beings endowed with
the appropriate faculties. It does not, however, explain just what
those faculties are, nor even how they are “made like”
their objects of perception. Minimally, though, Aristotle claims that
for some subject S and some sense object O:

S perceives O if and only if: (i)
S has the capacity requisite for receiving O’s
sensible form; (ii) O acts upon that capacity by enforming it;
and, as a result, (iii) S’s relevant capacity becomes
isomorphic with that form.

Each of these clauses requires unpacking. The plausibility of
Aristotle’s theory turns on their eventual explications. The first
clause (i) is intended to distinguish the active capacities of animals
from the merely passive capacities of lifeless material bodies,
including the media through which sensible forms travel. (Just as we do
not want to say that the tofu in the refrigerator perceives the garlic
next to it, we do not want to say that air perceives the color blue
when affected by the color of a car.) But it does not yet specify what
is required for having the requisite active capacities. Also difficult
is the notion of isomorphism appealed to in (iii). As stated, (iii)
invites, and has received, scrutiny. Interpretations range from
treating the form of isomorphism as direct and literal, so that, e.g.,
the eyes become speckled when viewing a robin’s egg, to attenuated,
where the isomorphism is more akin to that enjoyed between a house and
its blue-print. Here especially the plausibility of Aristotle’s
hylomorphic analysis of perception hangs in the balance.

Aristotle describes mind (nous, often also rendered as
“intellect” or “reason”) as “the part of the soul by which it
knows and understands” (De Anima iii 4, 429a9–10; cf.
iii 3, 428a5; iii 9, 432b26; iii 12, 434b3), thus characterizing it in
broadly functional terms. It is plain that humans can know and
understand things; indeed, Aristotle supposes that it is our very
nature to desire knowledge and understanding (Metaphysics i 1,
980a21; De Anima ii 3, 414b18; iii 3, 429a6–8). In this way,
just as the having of sensory faculties is essential to being an
animal, so the having of a mind is essential to being a human. Human
minds do more than understand, however. It is equally essential to the
human being to plan and deliberate, to ponder alternatives and
strategize, and generally to chart courses of action. Aristotle
ascribes these activities no less than understanding and contemplation
to mind and consequently distinguishes the “practical mind” (or
“practical intellect” or “practical reason”) from “theoretical mind”
(or “theoretical intellect” or “theoretical reason”) ( Nicomachean
Ethics vi 8 1143a35-b5; see
Aristotle: ethics).
In all these ways,
investigating this capacity of soul thus has a special significance for
Aristotle: in investigating mind, he is investigating what makes humans
human.

His primary investigation of mind occurs in two chapters of De
Anima, both of which are richly suggestive, but neither of which
admits of easy or uncontroversial exposition. In De Anima iii
4 and 5, Aristotle approaches the nature of thinking by once again
deploying a hylomorphic analysis, given in terms of form reception.
Just as perception involves the reception of a sensible form by a
suitably qualified sensory faculty, so thinking involves the reception
of an intelligible form by a suitably qualified intellectual faculty
(De Anima iii 4, 429a13–18). According to this model, thinking
consists in a mind’s becoming enformed by some object of thought, so
that actual thinking occurs whenever some suitably prepared mind is
“made like” its object by being affected by it.

This hylomorphic analysis of thinking is evidently a simple
extension of the general model of hylomorphic change exploited by
Aristotle in a host of similar contexts. Accordingly, Aristotle’s
initial account of thinking will directly parallel his analysis of
perception (De Anima iii 4, 429a13–18). That is, at least in
schematic outline, Aristotle will offer the following approach. For any
given thinker S and an arbitrary object of thought
O:

S thinks O if and only if: (i)
S has the capacity requisite for receiving O’s
intelligible form; (ii) O acts upon that capacity by enforming
it; and, as a result, (iii) S’s relevant capacity becomes
isomorphic with that form.

Unsurprisingly, the same questions which arose in the case of
perception also arise here. Most immediately, to understand Aristotle’s
approach to thinking, it is necessary to determine what it means to say
that a thinker’s mind and its object become isomorphic.

Here, at least, Aristotle points out what is obvious, that when a
thinker’s soul is made like its cognitive object, it does not become
one with some hylomorphic compound, but with its form: “for it is
not the stone which is in the soul, but its form” (De
Anima iii 8, 431b29–432a1; cf. iii 4, 429a27). The suggestion is,
then, that when S comes to think of a stone, as opposed to
merely perceiving some particular stone, S has a faculty which
is such that it can become one in form with that stone. Aristotle
sometimes infers from this sort of consideration that thought is of
universals, whereas perception is of particulars (De Anima ii
5, 417b23, Posterior Analytics i 31, 87b37–88a7),
though he elsewhere will allow that we also have knowledge of
individuals (De Anima ii 5, 417a29; Metaphysics xiii
10, 1087a20). These passages are not contradictory, since Aristotle may
simply be emphasizing that thought tends to proceed at a higher level
of generality than perception, because of its trading in comparatively
abstract structural features of its objects. A person can think of what
it is to be a stone, but cannot, in any direct and literal sense of the
term, perceive this.

However that may be, Aristotle’s conception of thinking implicates
him in supposing that thought involves grasping the structural features
of the objects of thought. To take an initially favorable case, when
thinking that tree frogs are oviparous, S will be in
a psychic state whose internal structural states are, among other
things, one in form with tree frogs. Since S’s soul does not
become a tree frog when thinking of tree frogs (DeAnima iii 8, 431b24–30), this form of isomorphism cannot be
mere instantiation of the form being a tree frog. Rather,
S’s mind will evidently be one in form with the tree frog, to
revert to our earlier analogy, in something like the way a blueprint
and the house of which it is the blueprint are one in form. There must
be a determinate and expressible structural isomorphism, even though
one could not say that the blueprint realizes the form of the house.
Houses are, after all, necessarily three-dimensional.

For Aristotle, it is not a contingent state of affairs that
S’s mind does not realize the form being a tree frog in the
way that tree frogs themselves do. On the contrary, the mind
cannot realize a broad range of forms: the mind is, according
to Aristotle, not “mixed with the body”, insofar as it,
unlike the perceptual faculty, lacks a bodily organ (De Anima
iii 4, 429a24–7). As such, it would not be possible for the mind to
realize the form of a house in the way bricks and mortar instantiate
such a form: houses provide shelter, something a mind, so understood,
cannot do. Consequently, when claiming that minds become isomorphic
with their objects, Aristotle must understand the way in which minds
become enformed as somehow attenuated or non-literal. Perhaps, though,
this should be plain enough. If a mind thinks something by being made
like it, then the way it is likened to what it thinks must be somehow
representational. Consequently, Aristotle is reasonably understood as
holding that S thinks some object of thought O
whenever S’s mind is made like that object by representing
salient structural features of O by being directly isomorphic
with them, without, that is, by simply realizing the form of O
in the way O does.

This approach to the nature of thinking has some promising features.
Both in its own terms and in virtue of its fitting into a broader
pattern of explanation, Aristotle’s hylomorphic analysis merits serious
consideration. At the same time, one of its virtues may appear also as
a vice. We noted in discussing Aristotle’s hylomorphic analysis of
change generally that his account requires the existence of suitably
disposed subjects of change. Only surfaces can be affected so as to be
changed in color. An action, such as Socrates’ becoming unnerved by a
glance of Alcibiades, cannot be made white; it is simply not the
appropriate sort of subject. So, hylomorphic change requires at least
the following two components: (i) something pre-existing to be the
patient of the change, and (ii) that thing’s being categorially suited
to be changed in the way specified.

Already at the first stage, however, Aristotle’s application of this
hylomorphic analysis of change to thinking may seem an over-extension.
For he maintains directly that mind is “none of the things
existing in actuality before thinking” (De Anima iii 4,
429a24). His reasons for maintaining this thesis are complex, but
derive ultimately from the forms of plasticity Aristotle believes the
mind must manifest if it is to be capable of thinking all things
(De Anima iii 4, 429a18). Now, if the mind is indeed nothing
in actuality before thinking, it is hard to understand how the
hylomorphic analysis of change and affection could be brought to bear
in this arena. If some dough is made cookie-shaped, it is actually
dough before being so enformed; even the sense organs, when made like
their objects, are actually existing organs before being affected by
the objects of perception. So, given a conception of mind as not
existing in actuality before thinking, it is hard to appreciate how
thinking lends itself to an analysis in terms of any recognizable
hylomorphic approach to change.

How great a problem this will be depends in part upon how entrenched
Aristotle’s commitment to the mind’s being nothing in actuality before
thinking turns out to be. It equally turns on how adaptable Aristotle’s
hylomorphic account of change proves to be. On this latter point,
Aristotle notes that according to his account, there are various
different types of change and alteration, illustrated by the difference
between a brown fence’s being painted white and a builder’s taking up
his tools and beginning to build. In the first case, there is a
destruction and a loss, of the fence’s original color; in the second
case, nothing is destroyed, but rather that which is already
dispositionally F becomes occurently F by engaging in
some F-ish activity. A builder is as such already able to
build. When he begins building he becomes fully and actually a builder
for the duration of his working. In this way, he loses nothing, but
instead realizes an already established potential.

This second type of change, which Aristotle maintains is the
appropriate model for many psychic activities, is either “not an
instance of alteration … or is a different kind of
alteration,” where one “should not speak of being affected,
unless <one allows that> there are two kinds of alteration”
(De Anima ii 5, 417b6–16). Perhaps Aristotle’s position will
then be that the mind, at least insofar as its cognitive capacities for
thought are concerned, is simply such as to be enformed by any of an
infinite range of objects of thought. This would involve its being
nothing determinate in itself; and far from being anomalous for
Aristotle, the mind would be in the cognitive realm precisely what the
most basic stuff, if there is a most basic stuff, would be in the
material realm. Both would manifest unconstrained plasticity; and so
each would be characterized essentially in terms of their range of
potentialities.

That said, it should be noticed that when it is detached from the
idiosyncratic thesis that the mind is nothing in actuality before
thinking, Aristotle’s hylomorphic analysis of thought retains whatever
plausibility it may have independently. For the suggestion that
thinking is to be understood at least partially in terms of
isomorphisms between our representational capacities and the objects of
our cognition has had, for good reason, a durable appeal. To the degree
that hylomorphism is generally defensible, then, its application in
this domain provides a theoretically rich framework for investigating
the nature of thought.

In both perception and thinking, animal souls are in some ways
active and in some ways passive. Although both mind and the sensory
faculty receive their correlative forms when perceiving or thinking,
neither is wholly passive in its defining activity. Perception involves
discrimination, while thinking involves selective attending and
abstraction, both activities, in the sense that each requires more than
mere passive receptivity. Still, the sorts of activity required for
cognition and perception do not explain in any obvious way another
central fact about human beings and other animals: animals propel
themselves through space in pursuit of objects they desire. Even in his
first characterizations of soul in De Anima, Aristotle is
alive to the widely held conviction that the soul is implicated in
motion (De Animai 2, 405b11; i 5 409b19–24). Of course, this
is a natural connection for him to make, given that every animate
being, that is, every being with a soul, has within it a principle of
motion and rest. So, it seems deeply characteristic of living systems
that they are able to move themselves in ways likely to result in their
survival and flourishing. Animals move themselves, however, in a
distinctive way: animals desire things, with the result that
desire is centrally implicated in all manner of animal action. Why did
ostrich run from the tiger? Because, one says easily, it desired to
survive and so engaged in avoidance behavior. Why did the human being
drive to the opera and sit quietly in her seat? Because, it seems, she
desired to hear the music and to observe the spectacle.

In these, as in countless other cases, the explanation of animal
action, human and non-human alike, easily and unreflectively appeals to
desire. This is why Aristotle does not end his De Anima with a
discussion of mind. Instead, after discussing mind, he notes that all
animals are capable of locomotion, only to deny that any one of the
faculties of the soul so far considered (viz. nutrition, perception, or
mind) can account for desire-initiated movement. Although he had
initially identified only these three faculties of soul (De
Anima ii 2, 413b12), Aristotle now notes that something must
explain the fact that animals engage in goal-directed behavior in order
to achieve their conscious and unconscious goals. The wanted
explanation cannot, he urges, be found somehow in the nutritive
faculty, since plants, as living beings, have that power of soul, but
do not move themselves around in pursuit of their goals; nor is it due
to perception, since even some animals have this faculty without ever
moving themselves at all, in any way (Aristotle evidently has in mind
sponges, oysters, and certain testacea, Historia Animalium i
1, 487b6–9; viii 1 588b12; Partibus Animalium iv 5, 681b34,
683c8); nor again can it be a product of mind, since insofar as it is
contemplative, mind does not focus upon objects likely to issue in
directives for action, and insofar as it does commend action, mind is
not of itself sufficient to engender motion, but instead relies upon
appetite (De Anima iii 9, 432b14–33a5). Indeed, using the same
form of reasoning, that a faculty cannot account for purposive action
if its activity is insufficient to initiate motion, Aristotle initially
concludes that even desire itself (orexis) cannot be
responsible for action. After all, continent people, unlike those who
are completely and virtuously moderate, have depraved desires but do
not, precisely because they are continent, ever act upon them (De
Anima iii 9 433a6–8; cf. Nicomachean Ethics i 13,
1102b26). So their desires are insufficient for action. Consequently,
he concludes, desire alone, considered as a single faculty, cannot
explain purposive action, at least not completely.

Ultimately, though, Aristotle does come to the conclusion that there
is a faculty of desire (orektikon) whose occupation it is to
initiate animal motion. (Perhaps his initial reservations pertained
only to one species of desire considered in isolation.) In any case, he
says plainly: “It is manifest, therefore, that what is called
desire is the sort of faculty in the soul which initiates
movement” (De Anima iii 10, 433a31–b1). He understands
this conclusion, however, in tandem with another which also serves as a
qualification of his earlier finding that mind cannot be the source of
motion. He holds, in fact, that it is reasonable to posit two faculties
implicated in animal movement: desire and practical reason (De
Anima iii 10, 433a17–19), though they do not work in isolation
from one another. Rather, practical reason, broadly construed to
incorporate the kind of image-processing present in non-human animals,
is a source of movement when it focuses upon an object of desire as
something desirable. So, practical reason and desire act corporately as
the sources of purposive motion in all animals, both human and
non-human (De Anima iii 10, 433a9–16), even though,
ultimately, it is desire whose objects prick practical intellect and
set it in motion (De Anima iii 10, 433a17–2). For this reason,
Aristotle concludes, there is a faculty of desire whose activities and
objects are primarily, if not autonomously or discretely, responsible
for initiating end-directed motion in animals. What animals seek in
action is some object of desire which is or seems to them to be
good.

Aristotle displays some hesitation in his discussion of desire and
its relation to practical reason in the aetiology of animal action.
Some have consequently concluded that his treatment can be regarded as
at best inchoate or, worse, as positively befuddled. There seem to be
no grounds for any such harsh assessment, however. Equally likely is
that Aristotle is simply sensitive to the complexities involved in any
approach to the intertwining issues in the philosophy of action. Unlike
some later Humeans, he evidently appreciates that the data and
phenomena in this domain are unstable, wobbling and retreating at the
approach of taxonomizing theory. The antecedents of action, he rightly
concludes, involve some sort of faculty of desire; but he is reluctant
to conclude that desire is the sole or sufficient faculty implicated in
the explanation of purposive behavior. In some way, he concludes,
practical reason and imagination have indispensable roles to play as
well.

Hamlyn, D. W., 1968 [1993], Aristotle De anima, Books II and
III (with passages from Book I), translated with Introduction and
Notes by D.W. Hamlyn, with a Report on Recent Work and a Revised
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Hicks, Robert Drew, 1907, Aristotle, De anima, with
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