Plato’s Theory of Forms

by Ian Bruce © Copyright 1998

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Plato expounded his Theory of Forms over a writing career of some forty years. The theory was being refined over this period and is never fully explained in any one dialogue. Thus, any explanation of the theory, involves piecing together fragments as they appear throughout Plato's writings, and recasting the earlier statements in the light of the metaphysical framework developed in the later works.

General Statement of the Theory of Forms

The theory basically postulates the existence of a level of reality or "world" inhabited by the ideal or archetypal forms of all things and concepts. Thus a form exists, for objects like tables and rocks and for concepts, such as beauty and justice. In the dialogue Meno, Plato describes a form as the "common nature" possessed by a group of things or concepts. Speaking of virtue he says:

And so of the virtues, however many and different they may be, they have all a common nature which makes them virtues; and on this he who would answer the question, "What is virtue?" would do well to have his eye fixed.

The forms are eternal and changeless, but enter into a partnership with changeable matter, to produce the objects and examples of concepts, we perceive in the temporal world. These are always in a state of becoming, and may participate in a succession of forms. The ever changing temporal world can thus, only be the source of opinion. Plato likens the opinions derived from our senses, to the perception of shadows of real objects, cast upon the wall of a cave. True knowledge however, is the perception of the archetypal forms themselves, which are real, eternal, and unchanging.

Whilst the forms are invisible to the eye, our souls have participated in the eternal world of forms prior to being incarnate in a physical body, and retain a memory of them. Although this memory is not readily accessible to the conscious mind, its presence is sufficient, to enable our limited perceptions. Plato maintains however, that the philosopher can achieve a state of perceiving the forms directly, with his mind's eye, by: developing skill, in discerning the abstract qualities, common to groups of things and ideas, in the temporal world; by realizing these are merely hypotheses; and by employing the method of dialectic, to categorize and group the qualities in their correct relationships and order; using these hypotheses as stepping stones, to further hypotheses. Thus reason is able to construct a hierarchy of forms, to scale to the height of first principle and attain a state of true knowledge.

All learning Plato maintains, is but recollection, of what our soul already knows. In the dialogue Meno, Plato agrees that enquiry is impossible, because, unless we already knew something, we would not recognize, the subject about which we were inquiring. But adds, that enquiry is worthwhile, in that it can uncover our innate memory.

An Assessment of the Strengths and Weaknesses of the Theory

In assessing the Theory of Forms it is important to remember that Plato was a profound language theorist. In the dialogue Cratylus he states that the Gods call things by their correct names, but the names given by men are not always correct. As there is meant to be a form corresponding to every name, or concept used by man, the notion of correct, or incorrect names, becomes extremely relevant. He notes that an important aspect of the dialectician's art is the giving of names. Although, as he notes in The Republic, the names or categories derived by dialectic are merely hypotheses, which the reason can use as "steps and points of departure" into a world which is above hypotheses. Thus the use of words in the dialogues can be easily misinterpreted.

The great logical strength of the Theory of Forms is that it is a construction capable of adapting to all criticism: whilst there are archetypal forms that correspond to all terms used by man, many of the terms used by man are incorrect; only the Gods use correct names consistently. Whilst Socrates may be presented as agreeing with his interlocutors, this is usually a step in demonstrating their state of ignorance, and indeed that of Socrates. For in the true Socratic tradition the recognition of one's own ignorance, is seen as an advancement of knowledge. What is more, if a discussion results in confusion and seeming contradiction, then that too can be seen as the theory at work, for Plato develops in Philebus and Phaedo the notion that because the world of the senses, the "seen" world, is compounded and finite, the one archetypal form (the "unseen") gives rise to apparent opposites on that level.

It is important to realise that the Theory of Forms is an hypothesis that is proven by the process of inference to the best explanation. It is a grand image that identifies levels of reality, and metaphysical functionalities that Plato reasoned must exist, to make any sense of the world. The actual mechanical processes involved are only defined in a very abstract manner, but even here, the theory has a counter, in that man cannot presume to conceive of the physiology of the Gods.

Because the Theory of Forms is an inference to the best explanation, its true strength or soundness must be gauged by its continued use over time. The abstract nature of its definition makes it compatible with many systems of thought: some derived from Plato, others developed independently; some arising after Plato's time, others predating him. If we ask the question of why in the two thousand years of suppression of ideas and burning of books that has been the Christian era, Plato's dialogues have survived intact, we must answer that Plato's theories are fundamentally supportive of basic Christian doctrine.

Whilst the details of the mechanics are scanty, Plato's notion that the power to abstract and perceive the commonalties in apparent opposites is our "step and point of departure" to true knowledge, is a theme we can discern in all the great systems of human thought.

Finally, the notion of "the reason" is crucial in understanding Plato. Plato makes it clear that the reason is a higher, vaster faculty than intellect. The Theory of Forms is itself an hypothesis. The intellect and logic may follow after the image and devise explanations, but the hypothesis is firstly a creation of the imagination, "the logician can provide no rules for the formulation of an hypothesis".

Thus the great strengths of the Theory of Forms are the notions of levels of reality and human faculties, it identifies as existing, or needing to exist if life is to be intelligible. Its weaknesses spring from, and illustrate the inadequacies of human words and concepts to approach a description of the infinite or timeless. The theory still stands as a beacon after two and a half thousand years, attesting to the vast sweep of mind Plato was able to attain, using the simple means he found in himself and the strength he found by the acknowledgement of his own weakness.

Selections From Plato's Dialogues

All the following extracts from the dialogues of Plato have been taken from the collected works translated by Benjamin Jowett, 3rd Edition 1892 as published electronically on CD ROM, Library of the Future 3rd Edition, World Library Inc., Irvine CA, USA, 1991-1994. The page numbers of the original paper version have not been preserved in the electronic rendition.

From the SOPHIST

Str. Should we not say that the division according to classes, which neither makes the same other, nor makes other the same, is the business of the dialectical science?

Theaet. That is what we should say.

Str. Then, surely, he who can divide rightly is able to see clearly one form pervading a scattered multitude, and many different forms contained under one higher form; and again, one form knit together into a single whole and pervading many such wholes, and many forms, existing only in separation and isolation. This is the knowledge of classes, which determines where they can have communion with one another and where not.

From the MENO

Soc. How fortunate I am, Meno! When I ask you for one virtue, you present me with a swarm of

them, which are in your keeping. Suppose that I carry on the figure of the swarm, and ask of you,

What is the nature of the bee? and you answer that there are many kinds of bees, and I reply: But do bees differ as bees, because there are many and different kinds of them; or are they not rather to be distinguished by some other quality, as for example beauty, size, or shape? How would you answer me?

Meno. I should answer that bees do not differ from one another, as bees.

Soc. And if I went on to say: That is what I desire to know, Meno; tell me what is the quality in which they do not differ, but are all alike; would you be able to answer?

Meno. I should.

Soc. And so of the virtues, however many and different they may be, they have all a common nature which makes them virtues; and on this he who would answer the question, "What is virtue?" would do well to have his eye fixed: Do you understand?

Meno. I am beginning to understand; but I do not as yet take hold of the question as I could wish.

Soc. To what then do we give the name of figure? Try and answer. Suppose that when a person asked you this question either about figure or color, you were to reply, "I do not understand what you want, or know what you are saying," he would look rather astonished and say, "Do you not understand that I am looking for the [likeness among many]?" And then he might put the question in another form: "Meno," he might say, "what is that [likeness among many] which you call figure, and which includes not only round and straight figures, but all?" Could you not answer that question, Meno? I wish that you would try; the attempt will be good practice with a view to the answer about virtue.


Pro. Why, Socrates, they are opposed in so far as they spring from opposite sources, but they are

not in themselves opposite. For must not pleasure be of all things most absolutely like pleasure – that is, like himself?

Soc. Yes, my good friend, just as color is like color; – in so far as colors are colors, there is no difference between them; and yet we all know that black is not only unlike, but even absolutely opposed to white: or again, as figure is like figure, for all figures are comprehended under one class; and yet particular figures may be absolutely opposed to one another, and there is an infinite diversity of them. And we might find similar examples in many other things; therefore do not rely upon this argument, which would go to prove the unity of the most extreme opposites.


"Then I will try again; you will understand me better when I have made some preliminary remarks. You are aware that students of geometry, arithmetic, and the kindred sciences assume the odd and the even and the figures and three kinds of angles and the like in their several branches of science; these are their hypotheses, which they and everybody are supposed to know, and therefore they do not deign to give any account of them either to themselves or others; but they begin with them, and go on until they arrive at last, and in a consistent manner, at their conclusion?"

"Yes," he said, "I know."

"And do you not know also that although they make use of the visible forms and reason about them, they are thinking not of these, but of the ideals which they resemble; not of the figures which they draw, but of the absolute square and the absolute diameter, and so on – the forms which they draw or make, and which have shadows and reflections in water of their own, are converted by them into images, but they are really seeking to behold the things themselves, which can only be seen with the eye of the mind?"

From the PHAEDO

"And the uncompounded may be assumed to be the same and unchanging, where the compound is always changing and never the same? That I also think, he said. Then now let us return to the previous discussion. Is that idea or essence, which in the dialectical process we define as essence of true existence – whether essence of equality, beauty, or anything else: are these essences, I say, liable at times to some degree of change? or are they each of them always what they are, having the same simple, self-existent and unchanging forms, and not admitting of variation at all, or in any way, or at any time?"

"They must be always the same, Socrates," replied Cebes.

"And what would you say of the many beautiful – whether men or horses or garments or any other things which may be called equal or beautiful – are they all unchanging and the same always, or quite the reverse? May they not rather be described as almost always changing and hardly ever the same either with themselves or with one another?"

"The latter," replied Cebes, "they are always in a state of change."

"And these you can touch and see and perceive with the senses, but the unchanging things you can only perceive with the mind – they are invisible and are not seen?"

"That is very true," Cebes replied.

"Well, then," he added, "let us suppose that there are two sorts of existences, one seen, the other unseen. Let us suppose them. The seen is the changing, and the unseen is the unchanging."

"That may be also supposed," Cebes said.


"Yes, Socrates," said Parmenides, "that is because you are still young; the time will come, if I am not mistaken, when philosophy will have a firmer grasp of you, and then you will not despise even the meanest things; at your age, you are too much disposed to regard opinions of men. But I should like to know whether you mean that there are certain ideas of which all other things partake, and from which they derive their names; that similar things, for example, become similar because they partake of similarity; and great things become great, because they partake of greatness; and that just and beautiful things become just and beautiful, because they partake of justice and beauty?"

"Yes, certainly," said Socrates "that is my meaning."

"Then each individual partakes either of the whole of the idea or else of a part of the idea? Can there be any other mode of participation?"

"There cannot be," he said.

"Then do you think that the whole idea is one, and yet, being one, is in each one of the many?"

"Why not, Parmenides?" said Socrates.

"Because one and the same thing will exist as a whole at the same time in many separate individuals, and will therefore be in a state of separation from itself. Nay, but the idea may be like the day which is one and the same in many places at once, and yet continuous with itself; in this way each idea may be one; and the same in all at the same time."

"I like your way, Socrates, of making one in many places at once. You mean to say, that if I were to spread out a sail and cover a number of men, there would be one whole including many – is not that your meaning?"

"I think so."

"And would you say that the whole sail includes each man, or a part of it only, and different parts different men?"

"The latter."

"Then, Socrates, the ideas themselves will be divisible, and things which participate in them will have a part of them only and not the whole idea existing in each of them?"

"That seems to follow."

"Then would you like to say, Socrates, that the one idea is really divisible and yet remains one?"

"Certainly not," he said.

"Suppose that you divide absolute greatness, and that of the many great things, each one is great in virtue of a portion of greatness less than absolute greatness – is that conceivable?"


"Or will each equal thing, if possessing some small portion of equality less than absolute equality, be equal to some other thing by virtue of that portion only?"


"Or suppose one of us to have a portion of smallness; this is but a part of the small, and therefore the absolutely small is greater; if the absolutely small be greater, that to which the part of the small is added will be smaller and not greater than before."

"How absurd!"

"Then in what way, Socrates, will all things participate in the ideas, if they are unable to participate in them either as parts or wholes?"

"Indeed," he said, "you have asked a question which is not easily answered."

"Well," said Parmenides, "and what do you say of another question?"

"What question?"

"I imagine that the way in which you are led to assume one idea of each kind is as follows: You see a number of great objects, and when you look at them there seems to you to be one and the same idea, or nature, in them all. Hence you conceive of greatness as one."

"Very true," said Socrates.

"And if you go on and allow your mind in like manner to embrace in one view the idea of greatness and of great things which are not the idea, and to compare them, will not another greatness arise, which will appear to be the source of all these?"

"It would seem so."

"Then another idea of greatness now comes into view over and above absolute greatness, and the individuals which partake of it; and then another, over and above all these, by virtue of which they will all be great, and so each idea instead of being one will be infinitely multiplied."

"But may not the ideas," asked Socrates, "be thoughts only, and have no proper existence except in our minds, Parmenides? For in that case each idea may still be one, and not experience this infinite multiplication."

"And can there be individual thoughts which are thoughts of nothing?"

"Impossible," he said.

"The thought must be of something?"


"Of something which is or which is not?"

"Of something which is."

"Must it not be of a single something, which the thought recognizes as attaching to all, being a single form or nature?"


"And will not the something which is apprehended as one and the same in all, be an idea?"

"From that, again, there is no escape."

"Then," said Parmenides, "if you say that everything else participates in the ideas, must you not say either that everything is made up of thoughts, and that all things think; or that they are thoughts but have no thought?"

"The latter view, Parmenides, is no more rational than the previous one. In my opinion, the ideas are, as it were, patterns fixed in nature, and other things are like them, and resemblances of them – what is meant by the participation of other things in the ideas, is really assimilation to them."

"But if, said he, the individual is like the idea, must not the idea also be like the individual, in so far as the individual is a resemblance of the idea? That which is like, cannot be conceived of as other than the like of like."


"And when two things are alike, must they not partake of the same idea?"

"They must."

"And will not that of which the two partake, and which makes them alike, be the idea itself?"


"Then the idea cannot be like the individual, or the individual like the idea; for if they are alike, some further idea of likeness will always be coming to light, and if that be like anything else, another; and new ideas will be always arising, if the idea resembles that which partakes of it?"

"Quite true."

"The theory, then that other things participate in the ideas by resemblance, has to be given up, and some other mode of participation devised?"

"It would seem so."

"Do you see then, Socrates, how great is the difficulty of affirming the ideas to be absolute?"

"Yes, indeed."