An Introduction to Plato

Instructor: Dr. Jan Garrett

This page was slightly modified October 26, 2009.

Knowledge vs. Correct Belief
Dialectical Discovery of Truth
Platonic Dualism
The Realm of True Being
Three Psychologies
The Value of Justice
Political Justice
Philosopher Kings
Divided Line
Cave Allegory

Plato begins from Socrates, especially Socrates' idea about the close connection between virtue, happiness, and knowledge, but explores questions of epistemology, metaphysics and political philosophy which Socrates probably never addressed.


He had to deal with the question why some political leaders, such as Pericles or Aristides the Just, seemed to be good, even if this type of statesman was unable to give the sort of account of justice which Socrates demanded. The Socrates character also often points out that such allegedly virtuous personages were unable to teach others virtue, while an expert in another field, e.g., horsetraining or gymnastics, is able to transmit his knowledge to others.

In the Meno, the Socrates character makes a three-way distinction, adding the middle level:

full ignorance--inferior people
correct belief, opinion--apparently virtuous people without knowledge; they hit on the right thing through good luck, or some dispensation of the gods.
knowledge--characteristic of truly virtuous people

He reintroduces this three-way distinction later in the Republic.


Plato also had to face the demand that he explain how it is possible for dialectic to disclose or uncover, through the appropriate questioning of someone else (or himself) the moral truths which can be the basis for true virtue.

This problem is associated with the problem of making sense of philosophical inquiry. The inquirer is presumably looking for something. Either I already know what it is or I don't know. If I do not already know what it is, how can I recognize it when I encounter it? But if I already know what it is, why do I have to seek?

Once again, the answer lies in distinguishing various imperfect approaches to knowledge below true knowledge.

Here Plato has Socrates introduce his theory of recollection. Knowledge of the essences (soon to be called forms) is possible because, says S., our souls, or rather the intellectual power of the soul, saw the forms prior to their entrance into our present bodies. On the point of acquiring bodies, we forget the pure vision of Justice, Virtue, Courage, but retain a deeply entrenched memory which can, under the proper circumstances, be provoked to remember.

Recollection comes in various stages. Consider how we come to know justice.

(1) When we observe a particular just and honorable act, and recognize it as just and honorable, we have begun to recall.

(2) When we are able to do an act because we rightly take it to be honorable, we have made some progress. We will have recalled a little better.

These two stages correspond roughly to the stage of correct belief.

When, after prodding by someone like Socrates, (3) we eventually formulate a correct definition of justice, we have made further progress, but at first our comprehension of this definition will be limited and we will not see how it fits together with the proper accounts of other virtues such as courage, temperance. This is not yet full knowledge, but it is transitional.

Finally, (4) when we are able to give an account of the virtues and defend it against all comers, we will have truly recalled what our minds saw when our souls were out of our bodies; we will have knowledge, not belief.


The Meno and Phaedo build on Socrates' distinction between the body, on the one hand, and "the part of the person made better by justice and worse by injustice," on the other. Plato's Socrates adopts the theory of transmigration of souls and reincarnation. Moreover, in the Phaedo, he attempts to prove that the soul exists in an out-of-body state prior to, and after, life in a human body.

It is not clear whether he got theory of transmigration and reincarnation from the Pythagoreans or from the cult of Orpheus. But he seems to have thought that the idea of a soul detachable from the body was necessary (i) for a proper ethical, and therefore political, philosophy and (ii) for understanding the supersensible nature of the Forms.

In the Phaedo, he argues that the body is the source of all our woes, our excessive appetites and passions, and our quarrels over property, which frequently result in civil wars and wars between states. There he says that the true philosopher is turned away from the body, focussed on true being, which belongs to a changeless, eternal realm. The true philosopher will know, or be closest of all mortals to knowing, and he will not be tempted to do evil because he will not essentially be interested in the things that tempt us to do evil.

This extreme rejection of the body smacks of asceticism. Yet one can make the case that this asceticism is something of a fifth wheel for Plato. He does not require such an extreme position. I'll return to this point.

THE REALM OF TRUE BEING (See Rep. 476d-479d)

The true realm of being in Plato's philosophy has characteristics of Parmenides' ultimate reality:

sharply distinct from the realm of becoming or change or nature.

Unlike the monists, Plato does not suggest that true being is all that there is.

And true being itself is multiple: it consists of the forms [or the forms and the ideal numbers]. Each of the forms are, like Parmenides' One, timeless, changeless and unique. But there are many forms, related to each other, but distinct from each other.

The Forms are models or paradigms or patterns for order in the phenomenal or sensible world, and particular objects in the phenomenal world are imperfect approximations to the Form. For example, the justice of Socrates' conduct is an imperfect image of the Form of Justice. And a child's building block as a physical phenomenon is an imperfect image of the ideal cube.

Plato's view implies not only that phenomenal things are less real than Forms because they fall short of them, but also that they are more real than not-being because they participate in or reflect the pure being of the Forms.

The attitude of hostility towards the human body which we may take to be Platonic after reading well-known dialogues like the Phaedo is a result not of the theory of Forms as such, but of the Orphic or Pythagorean elements in Plato's philosophy. A Platonist might well hold that the human body is partly good and partly bad, as a result of its closeness to and distance from the true being of the Forms.


Plato develops different accounts of the soul depending on his interest.

In the Phaedo, where he is trying to prove the immortality of the soul, he emphasizes the soul's separability from the body, and its natural affinity to the invisible, intelligible, eternal forms. He speaks of the body as having desires, e.g., for physical pleasures and possessions; when the soul involves itself with material things, it is dominated by the body and not being true to its own nature.

In the Symposium, his dialogue concerning Eros or Love for..., although his ostensible subject is love, he really seems to be discussing the nature of the human soul. And he says that Eros is a philosopher, aware of the ignorance he possesses but striving for wisdom. The point seems to be that the human soul is actually intermediate between the realm of the body and the realm of the Forms.

The psychology presented in the Phaedo differs from the psychology presented in the Symposium in that the first aligns soul primarily with the Forms, the second treats it as bridging the gap between sensible things and intelligible ones, or able to bridge it.

The psychology of the Republic's central books (esp. IV) essentially ignores the body and analyzes the soul as divided into three parts or powers, the appetites (which take over the desires earlier associated with the body), reason (which has the capacity in the mature philosopher to comprehend the Forms), and an intermediate power called the thumeidetikon (spirited faculty, the source of our social feelings, e.g., affection for persons, loyalty, anger, above all, the desire for honor).

The tripartite theory of the soul employs two Heraclitean ideas: the soul is both one and many--one entity, but with more than one part; and the soul is a location where internal tension occurs, though Heraclitus would not have gone along with Plato's suggestion that in some persons this tension can be abolished.


Plato employs the tripartite theory of the soul to refute Thrasymachus' view that injustice is more consistent with happiness than justice (put forth by Thrasymachus in book I of the Republic) as well as Glaucon's claim that justice is at most a means to what is desirable (early in book II). To refute these views he needs to show that being just is inherently valuable to the individual.

1. The appetites and thumos do not, by themselves, set limits to their pursuit of their objects (pleasure and honor).

2. Without limits on our desires for pleasure and reputation, we not only come into conflict with others but, more importantly, the very powers of our own soul conflict with each other.

3. The solution to this internal conflict is to follow a rule of harmony and proportion within the soul, and this may be supplied by the rational faculty, when it is allowed to lead.

4. The soul will be just when the rational faculty leads and the other parts follow.

5. The just soul, which is in harmony, will be at peace with itself; it will not experience internal civil war.


The theory of political justice parallels the theory of individual justice. Corresponding to appetite, spirit and reason in the soul are the artisans and farmers, warriors, and guardians in the state. The task of the artisans and farmers is to produce, the warriors to defend, and the guardians to rule. When the guardians rule wisely and the other classes do their tasks, following the lead of the guardians, there will be no civil unrest; there will be internal harmony; the state will be just and happy.


Speaking for Plato, the character Socrates argues that the state can be reformed into a just and noble state only when there is a union of philosophical wisdom and political power, i.e., when philosophers become kings or kings become philosophers (Rep. V 473b-e).

He then has to clarify what philosophy is. He approaches this topic by comparing and contrasting the lover of wisdom, or philosopher, with other types of person.

Those who "fuss about their lessons" are like poor eaters; they lack a desire of the corresponding object. They are not philosophers.

Then there are those who "are glad to sample every subject," curious people. Curious people share with the lover of wisdom that they are motiviated not by desire for physical pleasure or honor but by desire for learning. Socrates compares them with theatre-goers and sightseers.

Socrates distinguishes the lovers of wisdom from sightseers (in the ordinary sense) and theatregoers, "[those] devoted to beautiful sounds and colors and shapes and to works of art which consist of these elements." The latter are lovers of many beautiful things (i.e., particulars). The philosophers, by contrast, are lovers of beauty itself, beauty as such. (475b-476b)

The Republic then distinguishes knowledge and ignorance in terms of their relation to reality and unreality. Knowledge is of reality, ignorance is related to unreality. (It orients itself to what is-not.) Belief falls in between, relating to what is and is not.

While the lover of wisdom is oriented towards reality, the lover of beautiful sights (or sounds) is oriented towards what is both unreal and real, i.e., toward what lies in the interval between reality and unreality. (476c-478d, 479c)

The welter of things which the masses conventionally regard as beautiful and so on mill around somewhere between unreality and perfect reality. (479d)

Those persons are properly called philosophical are those "who are devoted to everything that is real." (480a)

The highest object of knowledge, according to Plato's Socrates, is goodness, sometimes translated as "the Good." (Rep. VI 505a) .

Socrates reminds his friends of the principle that

All the things we (somtimes) refer to as a plurality (set of things having the same name or label) we also conversely count as belong to a single class by virtue of the fact that they have a single particular character and we say that the x itself is 'what really is.' (507b)
For example, there is an absolute Large, an absolute Small, an absolute Justice, etc. There are many good things, and many beautiful things, but also there is one absolute beauty (or the beautiful itself), one goodness (or the good itself).

This is the one-many distinction as Plato understands it, between the many visible F's and the one intelligible F.

Socrates explains how hearing differs from sight. (507c-508a) With hearing there is the organ of hearing and what is heard (sounds); with sight, there is the organ of sight and what is seen, but a third factor is required with sight, which is not required with hearing, i.e., light, which enables the seer to see.

The source of the light that enables the power of sight to see is, obviously, the Sun. (508a)

Plato is using an analogy to explain the role of the Good in relation to intelligence and intelligible objects:

Goodness is to intelligence and intelligible objects as the Sun is to [the power of] sight and visible objects.
Which is to say that goodness somehow "illuminates" the Forms so that our minds can grasp them.

What can we say about the Good?

(a) It gives the things we know their truth and their reality;
(b) It activates the power of knowing (intelligence).
(c) It is beyond truth, knowledge and being; it is of greater majesty and might.

THE DIVIDED LINE (Rep. 509d-511e):

1. Divisions of objects: The upper division is the intelligible, and it consists of forms (at the highest level) and mathematical objects). The lower division is the visible, and it consists of enduring visible (physical) objects (at the higher level) and images or surface appearances.

2. Corresponding to these four levels are four states of mind, beginning from the highest: knowledge (noesis), thought (dianoia), confidence (pistis), conjecture (eikasia).

3. Plato understands the lower levels as imperfect reflections or expressions of upper levels. Thus a shadow of a human being (an image) is an expression of a three-dimensional human being (enduring visible object), an act of justice (visible) is an expression of the Form of Justice.

4. How do enduring visible objects differ from likenesses or images? Likenesses are fleeting or superficial and their apparent reality dissolves upon cross-examination. In book X of the Republic, Plato gives the example of a painted bed, which is less real than a three-dimensional bed.

5. How do visible things [including likenesses] differ from intelligibles? Intelligibles cannot be properly grasped by the senses; the senses are the way we grasp visible things. Intelligibles do not come into being and pass away; visible things do. Intelligibles are subject to definition in a way that visible objects are not.

6. How do mathematical objects differ from Forms? For mathematicals, there are many of the same type; thus, in a triangle, there are three angles. In the mathematical proposition 1+1=2, there are two occurrences of the mathematical "1". Forms are unique. There is only one Justice itself, only one Beauty itself.

7. How knowledge differs from thought:

(i) Knowledge (noesis), according to Plato, makes no use of visible objects, while thought (dianoia) makes use of them. Plato has geometry in mind when he talks about thought. We draw a quasi-line in the sand when we are talking about intelligible lines.

(ii) Thought proceeds deductively from unquestioned assumptions while knowledge uses dialectic to rise to fully tested knowledge. Once again, Plato has geometrical theorems in mind when he speaks of thought, his own dialectical method when he speaks of knowledge.

THE CAVE ALLEGORY (Rep. VII 514a-517c):

1. Five levels:
a. the level at which the prisoner only "knows" the shadows and echoes as real;

b. the level at which the released prisoner sees the statues and the fire and comes to understand that they caused the shadows and echoes;

c. the level out of the cave at which the prisoner sees objects by moonlight, shadows by daylight, or reflections in pools of water;

d. the level at which the prisoner studies things by normal sunlight;

e. the level at which the prisoner sees the Sun and comes to grasp that it is the cause of everything she has seen, even the shadows deep in the Cave.

2. Correlation with Divided Line:

a. General: progress through stages to greater awareness.

b. Allegory: bottom four levels of C.A. correspond to four levels of divided line.

3. How allegory functions: An allegory "speaks" of something else (while seeming, on the surface, to speak about what it "obviously" means). Thus when Plato speaks of the Sun, he "obviously" means the Sun; allegorically, however, he means the Good. The Sun allegorically stands for or symbolizes the Good.

It is important not to confuse two relationships: "Y is allegorical symbol for X" differs from "Y is an example of X". The objects seen in daylight by the Prisoner allegorically stand for Platonic Forms. They exemplify enduring visible objects. In the Cave Allegory, Plato is not primarily interested in what they exemplify. Readers may be confused by the fact that the shadows in the Cave not only are, or exemplify, images, but they stand allegorically for the images or surface impressions.


The dialogue Timaeus presents a Platonic account of the creation of the kosmos. The details of this account cannot be taken up here, but I must note a few things about it.

In the story Plato tells, there are three eternal or everlasting things (if we group all the forms together as one thing): (1) the forms; (2) the divine Craftsman (demiourgos); (3) the "receptacle": A principle of disorder, which is also the ultimate matter to receive the imprint of the forms.

Plato believes that much of the order in nature requires a teleological explanation, that is, the parts of nature need an explanation in terms of the good each of them do for the whole of which it is part. The Craftsman embodies that convinction; it is He who has the intention to make the universe as good as He can.

On the other hand, there are imperfections in nature; these result from the 'receptacle', which has received the imprint of the Forms but continues to operate in the material objects of the visible world. Material reality is always a kind of compromise between the perfection of the Forms and the Craftsman, on the one side, and the disorder of the receptacle, on the other.

With the account in the Timaeus, Plato approximates Aristotle's theory of four causes. His account differs from the Judaeo-Christian story of creation in that the Craftsman works from preexisting forms and matter, whereas the J-C God, at least as interpreted by major theologians since Augustine, contains the Forms within Himself and creates the matter as well as formed matter of the universe.