© Michael Lacewing
Plato’s theory of Forms
From sense experience to the Forms
In Book V (476f.) of The Republic, Plato argues that all objects we experience through our senses are particular things. We don’t ever sense anything ‘abstract’, but always some individual thing or other. For example, we only ever see this particular beautiful thing or that particular beautiful thing, but we never see ‘beauty’. But, obviously, more than one thing can be beautiful. Beauty is a property that more than one thing can have. So, Plato claims, if many different things can be beautiful, then there is something they share in common, viz. beauty. So there must be something which is ‘beauty’, even though we never experience beauty itself through our senses. This idea of a universal, a property that more than one thing can have, is a first approximation to the idea of a Form. The Form of Beauty manifests itself in all the different things, in all the different ways, we call ‘beautiful’.
But why should we agree that just because many different things can be beautiful, there is some thing which is ‘Beauty’? Because, Plato goes on to argue, Forms exist independently of particular things. All particular beautiful things could also be destroyed, yet that won’t destroy beauty itself. So beauty must be a separate thing, existing in its own right. So, he concludes, particular things ‘share’ or ‘participate’ in the Forms, but these exist independently.
Plato gives another argument for this claiming, relating to the nature of knowledge, which we will return to in the next section.
Metaphysics of the Forms
In arguing that Forms exist independently of the particular things that ‘participate in’ them, Plato constructed an original and controversial metaphysics (one that Aristotle, for example, rejected). Plato discusses several essential properties of the Forms:
Self-predication: the Form of Beauty is itself beautiful. But this is different from the way in which all other beautiful things are beautiful. Every other beautiful thing is beautiful because it ‘participates in’ the Form of Beauty; but the Form simply is beautiful. It is what it is in virtue of itself. This also provides an explanation of why things that participate in Beauty are beautiful: participating in Beauty makes a particular thing beautiful because the Form is itself beautiful. Beauty is ‘transmitted’ to particular things that participate in it.
Independence from particulars: it follows from (1) that each Form is its own essence. Because this is what a Form is, we can understand why it is that Forms (can) exist independently of whether any particular object participates in them. Because it is its own essence, it is what it is regardless of whether particulars participate in it; it is not essential to its existence that it is exemplified in particulars. A Form, therefore, also does not exist in time or space (either at a particular space/time or as distributed across all particulars exemplifying it).
Perfection: a Form is the perfect example of itself. Nothing can be more beautiful than the Form of Beauty, and there is no way in which the Form is not beautiful. This is sometimes suggested as an important difference between ‘participating in’ and ‘being’ Beauty: all particular things only approximate to the property of beauty, which is only perfectly possessed by the Form.
Permanence: Forms do not change. The Form of Beauty cannot become not beautiful, nor can it have ever been not beautiful. If it changed, then by the new Form of Beauty, the previous Form would not have been perfectly beautiful; by the previous Form, any change would be a change away from being beautiful. As this is impossible, Forms do not change.
Simplicity: Plato repeatedly says the Forms are ‘one’. Each Form has just the one property of which it is the Form: the Form of beauty is only beautiful (and the only thing which is only beautiful). However, Plato also suggests that each Form is good, and that the Form of the Good is the Form of Forms. Furthermore, Plato attempts to give full accounts of each Form that explains what it is. For example, in The Republic, Plato argues that justice is doing one’s own job (433a). This equates justice to a particular set of properties, so it is not simple or just ‘one’.
In contrast to Forms, particulars are complex, changeable, and imperfect. These important differences suggest that the way Forms and particulars exist is different, and that the existence of the Forms is superior: they are in a way that particulars are not. Forms exist independently, but particulars only exist through participating in the Forms. Plato speaks of ‘two worlds’, the world of Forms and that of particulars. But if they are so different, how can particulars ‘share’ or ‘participate’ in the Forms at all?
One suggestion is that the properties particulars have are ‘copies’ of the Forms. The beauty of this rose is a copy of the Form of Beauty. While particulars are material (made of matter), they can possess properties that are copies of the Forms. Unlike the Forms, a particular can lose its properties (e.g. its beauty) and even cease to exist as that particular (a rose can become ash). A particular is what it is in virtue of the properties it has (e.g. a rose, beautiful, etc.). But its properties are how it participates in the Forms. So a particular only exists by participating in the Forms.
Knowledge, belief and ignorance
Plato’s second argument for separating the Forms from the particular things we experience with the senses relates to the nature of knowledge. Particular things will always both be X – have some property, e.g. beauty or largeness – and not-X, either at different times, or to different observers, or in different contexts. And so ‘can we say that any of these many things is, any more than it is not, what anyone says it is?’ (479b)
Plato argues that because particular things are what they are (beautiful, large, etc.) only relatively and transiently, there cannot be knowledge of them. Knowledge needs more permanence and certainty. He argues that we cannot know what is not true; knowledge is about truth, about what is. So if something both is and is not X, then we cannot know that it is X.
In contrast to particular beautiful things, the Form of Beauty is beautiful under all conditions, to all observers, at all times. The Form of Beauty is pure beauty; it alone is not both beautiful and not beautiful. It is therefore possible for us to acquire knowledge of the Forms. (As noted above, we can’t experience Forms through our senses. We have this knowledge through reason.) Because we can have knowledge of the Forms, but not knowledge of particular objects of sense experience, the Forms must be separate from particular things.
Plato’s argument relies on making a distinction between knowledge (epistémé) and doxa, translated as ‘belief’ or ‘opinion’. Just before giving the argument above, he argues knowledge and opinion are different ‘faculties’ for two reasons (477a-478e):
Knowledge is infallible – you cannot know what is false. Opinion, however, can be mistaken. So opinion cannot be knowledge.
Knowledge is only of what is real. We cannot have knowledge of what is not real or does not exist. Knowledge is ‘about’ what is real. By contrast, ignorance relates to what is not real, what does not exist, i.e. ‘nothing’. If you are completely ignorant of something, you don’t think of it at all; if you don’t understand it, you can’t form an opinion about its reality. If there is something between what is real and what is not real (which Plato argues there are, viz. particular things, which are both X and not-X), then there must be something between knowledge and ignorance. We know from (a) that opinion is not knowledge; but opinion is obviously not ignorance either, because opinions are always ‘about’ something or other. And opinion does seem to be between complete ignorance and knowledge.
According to (a), knowledge and opinion must have different powers. According to (b), knowledge and opinion must have different objects (what is real v. what is between what is real and what is not real). Therefore that about which we have opinions cannot be the same thing as that about which we have knowledge. Plato argues that opinion relates to the world of the senses, knowledge to the world of the Forms. So Forms must exist separately from particular things.
How can we acquire knowledge of the Forms?
Those people in Plato’s republic who eventually acquire knowledge of the Forms are those guardians who become philosophers. The guardians are trained in arithmetic, geometry and astronomy to bring them to dianoia. But to achieve noésis, the guardians must be additionally trained in dialectic, or philosophical argument. For further discussion of this argument, see the handout on ‘Plato’s similes of the Cave and the Divided Line’.
Plato argues that to gain knowledge of the Forms, a person must be ‘re-oriented’, away from being concerned and caught up in the world of the senses: ‘the mind as a whole must be turned away from the world of change until its eye can bear to look straight at reality, and at the brightest of all realities which is what we call the good’ (518c). The final step in the philosophers’ education is not so much about imparting knowledge, and but turning the mind towards the Forms. However, the question still remains how dialectic leads to an understanding of the Forms.
In fact, Plato doesn’t say. One theory is that, as shown in Plato’s The Republic and other dialogues, dialectic establishes both the existence and the nature of the Forms. Another relates to the fact that the Forms are ‘one-over-many’. A Form is unitary and simple, but many particular things can participate in it. There is only one Form of Beauty, but many things can be beautiful. Mathematics helps us to understand the idea of ‘one-over-many’, and helps us understand how the ‘one’ is the real essence that the many share in. For example, mathematics establishes the necessary properties that all triangles must have in common. And all existing triangles are triangles because they share the essential properties of the Form of the Triangle. Dialectic helps us understand this more generally, or abstractly, because it searches for a unifying account of each and every thing. Dialectic asks ‘what is justice?’ or ‘what is courage?’, and so we think about the abstract ideas, the Forms, of justice and courage.
Assessing Plato’s theory of knowledge
Knowledge and reality
Many philosophers reject Plato’s claim that knowledge must match something ‘real’ in the sense that Plato means, viz. things that don’t change and perfectly exemplify some property. Plato might be right that knowledge cannot change (it can’t go from truth to falsehood), but that doesn’t mean the object of knowledge can’t change. For example, I can know (it seems) that a particular object of sense experience – this book – has a particular property, e.g. it is a certain size, even though its size can change – if you burn it, for instance. What I know is that the book is this size now (at a specific moment in time), and this truth won’t change even if the size of the book changes. Plato seems to have confused a property about knowledge with a property about the object of knowledge.
From this, we can see that even if knowledge and opinion are different faculties because knowledge is infallible and opinion is not, that doesn’t mean that they have different objects. There is no need for the object (particular thing, Form) to match the epistemic state (opinion, knowledge). We can make the distinction in some other way, e.g. knowledge is always true and justified, whereas opinion can be false and unjustified.
Knowledge and certainty
Plato controversially sets the standard for knowledge very high, which has perhaps inspired sceptics ever since. Because knowledge by definition cannot be false, it seems he believes that knowledge must involve certainty. If we cannot be certain, we cannot know. Plato argues we can have certainty about the Forms, and so know them, because they are unchanging; but we cannot be certain of, or have knowledge of, particular objects of sense experience. But we can reject the claim that knowledge requires certainty, and argue instead that it requires only justification. In fact, Plato put forward an argument of this kind in the Theaetetus.
Plato’s conclusion is that only nous delivers knowledge of reality. However, we have seen that his account of how nous works, how we finally achieve noésis, is not clear. After all, unlike in the case of sense experience being caused by physical objects, Plato didn’t claim that the Forms cause our knowledge of them. So what is the means by which nous knows the Forms?
Hume argues, indirectly, that there is no such thing as nous. There are only two sorts of knowledge: what reason can demonstrate (a priori knowledge), and what we confirm through the senses (a posteriori knowledge). But, Hume argues, reason can only demonstrate analytic truths. It can’t provide ‘insight’, i.e. it cannot prove synthetic truths. It is not surprising that Plato cannot give us a clear account of how nous works if there is no such thing!
Plato’s best form of defence is probably attack. He could argue that unless we allow that there is such a thing as rational insight, we will fall into scepticism. For example, the first knowledge of the Forms we have is through mathematical reasoning. If he can argue successfully that this knowledge is based on reason, but isn’t analytic, then his theory is supported – even if he can’t then give us an account of how we have knowledge of the Forms. In other words, Plato can argue that we need rational insight to account for mathematical knowledge. If the argument from mathematical knowledge doesn’t work, Plato could try the same argument in some other area of knowledge, e.g. moral knowledge.
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