Three Platonic Theories

The Tripartite Theory of the Soul

In the Republic, Socrates argues the soul consists in more than reason. He argues that the soul has reason but that it also has two parts without reason. In this way, the soul is tripartite:

All three parts of the soul have desires. The desire in reason is or stems from beliefs about what is good and what is bad. This, however, is not true of the appetite and spirit. The desires in these parts arise independently of any beliefs about what is good and what is bad.

The Argument from Opposites

"Is there something in the soul of those who are thirsty but refuse to drink, something bidding them to drink and something different, something forbidding them, that overrides the thing that bids them to drink? And doesn't the thing that forbids in such cases come into play, if it comes into play, as a result of calculation (λογισμοῦ), while what drives and drags them to drink is a result of feelings (παθημάτων) and diseases? Hence isn't it right for us to claim that they are two, and different from one another? We'll call the part of the soul with which it reasons the λογιστικὸν and that with which it lusts, hungers, thirsts, and feels other appetites, the irrational (ἀλόγιστόν) and appetitive part (ἐπιθυμητικόν), companion of indulgences and pleasures" (Republic IV.439c).

"It is obvious that the same thing will never do or suffer opposites in the same respect in relation to the same thing and at the same time. So that if ever we find this happening we shall know that it was not the same thing but a plurality" (Republic IV.436b).
To understand the Tripartite Theory, consider a case in which someone is thirsty but refuses to drink. Socrates thinks there are two desires in play. One stems from appetite (the desire to drink). This desire arises in reaction to events in the body. In the absence of a desire from reason, this appetitive desire would move the person to drink. Reason, however, because it has the belief that in the circumstance drinking is not good, has the desire not to drink. If reason rules, the path from the appetite to action is interrupted. Reason overrides the appetite.

Socrates argues for this understanding in terms of a principle about opposite motions.

In this argument, he conceives of desire and aversion as opposite motions of the soul. Desire is a motion toward, and aversion is a motion away. If a person is thirsty, he has a motivation to drink. If he thinks that drinking is not in his best interest, he also has a motivation not to drink. If this desire and aversion are opposite motions, then given the principle about opposite motions, Socrates concludes that this desire and aversion are motions of different parts of the soul. The appetitive part of the soul has the desire, and the part of the soul that reasons has the aversion.

  Of the spirit (θυμοῦ), that with which we feel anger (θυμούμεθα), is it a third, or would it be the same as these [we have distinguished]?
  Perhaps with one of these, the appetitive.
  But I once heard a story which I believe, that Leontius the son of Aglaion, on his way up from the Peiraeus under the outer side of the northern wall, becoming aware of dead bodies that lay at the place of public execution at the same time felt a desire to see them and a repugnance and aversion, and that for a time he resisted and veiled his head, but overpowered in despite of all by his desire, with wide staring eyes he rushed up to the corpses and cried, ‘There, ye wretches, take your fill of the fine spectacle!'
  I too have heard the story.
  Yet, surely, this anecdote signifies that the principle of anger sometimes fights against desires as an alien thing against an alien.
  Yes, it does, Socrates" (Republic IV.439e).

  "So in the soul, there is the spirited part (θυμοειδές), which is the helper of reason by nature (τῷ λογιστικῷ φύσει) unless it is corrupted by bad nurture?
  We have to assume it as a third, Socrates.   Yes, provided it shall have been shown to be something different from the rational, as it has been shown to be other than the appetitive.
  That is not hard to be shown, Socrates. For that much one can see in children, that they are from their very birth chock-full of rage and high spirit, but as for reason, some of them, to my thinking, never participate in it, and the majority quite late.
  Yes, by heaven, excellently said, and further, one could see in animals that what you say is true" (Republic IV.441a).
In addition to the part with reason and the part with appetites, Socrates argues for a third part of the soul. He says, in the case of Leontius (Republic IV.439e-440a), that some part of the soul conflicts with appetite and that children have spirit but "as for reason (λογισμοῦ), some of them... never participate in it, and the majority quite late" (Republic IV.441a). The argument in these remarks seems to be that examples of the conflict in the case of Leontius occur in children and animals (Republic IV.441b) but that since animals lack reason and reason does not play a controlling role in the actions of children, there must be a third part of the soul. This part is spirit.

The Harmonious Organization of the Parts

Given the Tripartite Theory, there are different possible organizations among the parts of the soul. The proper organization is the one in which reason rules, spirit is reason's ally, and appetite is suppressed. When the parts are so organized, they are in "harmony." Since reason knows what is good and what is bad, a human being whose soul is in "harmony" acts for the sake of the good.

  "Is it appropriate (προσήκει) for the reasoning part to rule, since it is wise and exercises foresight on behalf of the whole soul, and for the spirited part to obey and be its ally?
  Assuredly, Socrates" (Republic IV.441e).

How Spirit and Appetite generate Action

"The same magnitude viewed from near and from far does not appear equal. And the same things appear bent and straight to those who view them in water and out, or concave and convex, owing to similar errors of vision about colors. There is every confusion of this sort in our souls, but measuring and numbering and weighing prevent the domination in our soul of the apparently greater or less or more or heavier, and give the control to that which has reckoned and numbered or even weighed. This would be function of the part of the soul that reasons and calculates (λογιστικοῦ). Sometimes, when this has measured and declares that certain things are larger or that some are smaller than the others or equal, there is at the same time an appearance of the contrary. But we said that it is impossible for the same thing at one time to hold contradictory opinions about the same thing. It follows, then, that the part of the soul that opines (δοξάζον) in contradiction of measurement could not be the same with that which conforms to it. Further, that which puts its trust in measurement and reckoning must be the best part of the soul. That which opposes it must belong to the inferior elements of the soul. This, then, was what I wished to have agreed upon when I said that poetry, and in general the mimetic art, produces a product that is far removed from truth in the accomplishment of its task, and associates with the part in us that is remote from intelligence, and is its companion and friend for no sound and true purpose" (Republic X.602c).
Appetite and spirit can move a human being to action. For this to be possible, there must be representations of the states of affairs that are the objects of the desires in appetite and spirit.

What are these representations? Are they beliefs about how the world is?

One might think that that these representations are beliefs. In the parts of the soul without reason, one might think that sensation, imagination, and memory form beliefs. Because they are formed without reason, these representations are formed uncritically. They are formed without reasoning about whether the world is the way these representations represent it to be.

Is this how Plato understands how appetite and spirit can cause action?

In Book X of the Republic, in the context of the argument against imitation and imitative poetry, Socrates seems to commit himself to the view that the parts of the soul without reason can have beliefs. He seems to argue that sometimes there is a belief in the part of the soul with reason that is opposite to a belief in one of the parts of the soul without reason.

In the Timaeus, however, which is traditionally thought to be a late dialogue, Plato seems to have a different view of what belief is. He has Timaeus say that the appetitive part of the soul is "completely devoid of belief (δόξης), reasoning (λογισμοῦ), and thought (νοῦ)" (Timaeus 77b). The suggestion is that belief is strictly an achievement of reason.

One way to understand these different conceptions of belief is to suppose that Plato came to think that belief is a matter of reason and that what looks like a belief in the parts of the soul without reason is a psychological state of a different kind. If this interpretation is correct, then one would expect Plato to work out this new understanding in some dialogue.

The Theaetetus is traditionally thought to be a late middle or late dialogue written before the Timaeus.

Theaetetus, the historical figure, was an Athenian mathematician who work in the theory of incommensurable quantities. He died died from wounds and dysentery on his way home after fighting in an Athenian battle at Corinth.
In fact, Plato does work out this view in the Theaetetus.

  "Theaetetus, do you define thought (διανοεῖσθαι) as I do?
  How do you define it, Socrates?
  As the talk (λόγον) which the soul has with itself about any subjects which it considers. You must not suppose that I know this that I am declaring to you. But the soul, as the image presents itself to me, when it thinks (διανοουμένη), it is conversing with itself, asking itself questions and answering, affirming and denying. When it has arrived at something definite, whether slowly or suddenly, and is at last agreed and is not in doubt, we call that its belief; and so I define forming a belief as talking and a belief (δόξαν) as talk which has been held, not with someone else, nor yet aloud, but in silence with oneself" (Theaetetus 189e).
The Theaetetus is an investigation into what "knowledge" (ἐπιστήμη) is (145e). Theaetetus suggests that "knowledge is nothing else than perception" (οὐκ ἄλλο τί ἐστιν ἐπιστήμη ἢ αἴσθησις) (151e). In 184b, to refute this understanding of what knowledge is, Socrates says that the soul grasps some things through the senses and some things in some other way. For example, he says that we perceive color through the eyes and sound through the ears. The senses in this way grasp sensible features of the world, but the senses do not form beliefs because they do not grasp predicates. The application of predicates is an achievement of the part of the soul with reason. At 186b, Socrates gives an example that makes this a little clearer. He says that the soul perceives hardness through the sense of touch. Hardness is a sensible feature of the world, but to predicate hardness of the thing that the sense of touch perceives and thus to form the belief that this object is hard, the soul must grasp the predicate "is hard" and that to grasp this predicate the soul must know that hardness is, that softness is, and that these things are opposites.

The Philebus is traditionally thought to be a late dialogue.
The Philebus provides some explanation of a way in which the parts of the soul without reason are capable of providing representations of the world that are motivating.

In the Philebus, Socrates provides accounts of perception, memory, and desire. He says that perception involves the soul and the body (34a) and that memory is the preservation of perception (34a). Socrates says that hunger and thirst are desires (34d), that they occur in the presence of depletion, and are for (the opposite) replenishment (35a). For a living thing to have the desire for a given replenishment, it must represent the replenishment in some way (35b). Socrates says that memory supplies the representation. Memory supplies the representation that represents the object of the desire (35b-d). Socrates does not make the point explicitly, but presumably memory also provides the representation of how to acquire the object of the desire.

In this discussion in the Philebus, Socrates makes it clear that this understanding applies to both animals and human beings. Only human beings have beliefs because only human beings have reason. Socrates suggests that beliefs are accompanied with the images that alone are the means of representation in animals. He compares the soul to an illustrated book. Forming a belief is like writing a sentence in the soul (38e-39a). In addition to the "writer" in the soul, Socrates says that there is an illustrator who makes illustrations of the words the writer has written (39b).

How Reason Rules Spirit and Appetite

Given that it is "appropriate for the reasoning part to rule" the other two parts of the soul (Republic IV.441e4), there must be some way or ways for reason to control these parts.

It is through the extensive eduction and system of censorship in the Republic that this control occurs. The society is organizes so that when a person is young the appetitive and spirited part of his soul become habituated to having the desires reason deems to be correct, and it may be that one way this habituation occurs is in terms the illustrations discussed in the Philebus.

In the Timaeus, the gods who fashioned the mortal parts of the soul knew the appetitive part would not understand reasons but would be enticed by "images and appearances" (εἰδώλων καὶ φαντασμάτων) (71a). Consequently, they fashioned the appetitive part in the body in such a way that the intellect can "show" it images. This causes pain or pleasure (71b-d). In the Philebus, in the discussion of pleasures of anticipation, there is an indication of how this might happen. In pleasures of anticipation, when memory supplies the image of replenishment (that provides the object of the desire), there is anticipatory pleasure in the expected replenishment (36b). This suggests a way for reason to rule appetite and spirit: reason can use the mechanism that underlies anticipatory pleasure and pain to control the parts of the soul without reason.

"For I fancy that you have long observed how men do not experience fear or distress when they have been rationally persuaded that evil is present or is approaching, but they do so when they get an image (φαντασίας) of those same things. For how could you stir the irrational by means of reason, unless you place before it a picture, as it were, that resembles a picture perceived by the eye? Thus some persons fall victim to desire as a result of a verbal account, and when given a vivid injunction to flee the charging lion, even though they have not seen it they are afraid" (Galen quoting Posidonius, The Doctrines of Plato and Hippocrates V). Consider a compulsive behavior, such as smoking (to use a modern example). The appetite may form a habitual desire to smoke because smoking has been pleasurable in the past. Over time, this habit may become extremely strong. If, at some point, reason discovers that smoking is bad, this belief alone will not be enough to prevent the the appetite from issuing the desire and hence from moving the person to smoke. To break the habit, reason must form beliefs that imagine the painful consequences of smoking so that the appetitive part of the soul associates the pain depicted in these images with smoking and thus takes less anticipatory pleasure in smoking. Reason, in this way, can use imagination to recalibrate how strong the desire to smoke is in the appetite.

Perseus Digital Library:

Plato's Republic, Theaetetus, Timaeus, Philebus

Henry George Liddell, Robert Scott, A Greek-English Lexicon:
βούλησις, boulēsis, noun, "willing"
επιθυμία, epithymia, noun, "appetite"
θυμός, thymos, noun, "strong feeling or passion"
ὄρεξις, orexis, noun, "appetency, conation, including ἐπιθυμία, θυμός, βούλησις"

"There is reason to believe that [the historical] Socrates thought that " irrational part of the soul with its own needs and demands..." What is this? A part of the soul that does not engage in reasoning. In the tripartite soul, spirit and appetite are the "irrational" parts. They are parts without reason.

What does it mean to say that "[i]f reason knew the truth, it could never get confused in this way"? The answer, it seems, is that reason knows the truth when all its beliefs are true. In this case, no argument for a false conclusion whose premises are taken from the beliefs of reason is valid.
there is no such thing as acting against one's own better judgment. What does happen is that reason in certain circumstances gets confused and, instead of holding on to its better judgment, follows some other judgment. If reason knew the truth, it could never get confused in this way. Thus, according to Socrates, such cases reveal nothing but a failure of reason which in its weakness does not hold on to the true belief, but accepts a false one and acts on it. Plato, Aristotle, and their followers, on the other hand, believed that such cases could not be explained as purely intellectual failures, that one had to assume that besides reason there is an irrational part of the soul with its own needs and demands which may conflict with the demands of reason and which may move us to act against the dictates of reason, if reason has not managed to bring the irrational part of the soul firmly under its control" (Michael Frede, "The Stoic Doctrine of the Affections of the Soul," 96. Norms of Nature, edited by Malcom Schofield and Gisela Striker (Cambridge University Press, 1986) 93-110).

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