The theory of Forms is Plato's attempt to explain how we can group non-identical items under the same label, such as 'pen.' It is a result of Socrates' investigations into the real meaning of moral terms such as piety and justice, and how do we come to know what these are, even if we cannot express them. This seems to have spread in Plato's theories into what makes a particular object what we recognise it as, i.e. what is it that a fountain pen and a biro have in common that allows us to call them both pens.
There are two steps to the theory of Forms. The first is the Forms themselves, and whether they exist. The second is how we come to know them. According to Plato, Forms are the perfect template for each possible object and idea. Thus, there is a Form of Cat, of Triangle, of Piety, and so on. Anything which exists in this world has an ideal Form, and is perhaps a mixture of Forms, since an object can contain both Cat and Black. However, these objects that exist in our world, as opposed to the Forms, are not identical to the Forms, they are as it were imperfect copies. What allows us to recognise these dissimilar items as being grouped under the same name is that each relates to the perfect Form, if not to each other. Thus the diverse things we call leaves we recognise as such because they are all related to the perfect Form of leaf. One particular point that Plato makes about Forms is that they are eternal and unchanging, that although the shape of leaves may change throughout history, that is only because the process of copying the object from the Form changes, being imperfect anyway.
The second part of the theory is perhaps the more contentious. Plato claims that the Forms exist in another world, an intellectual realm, and that this is also where our soul goes when our bodies die. Our soul then encounters all the possible Forms, and they are stored in its memory (Plato believes that the soul and the rational part of the mind are one and the same) to be recalled later. He also claims that this had happened to us before we had been born, since he believes that the soul passes through infinite incarnations. The reason that we do not recognise everything from birth is that the very act of giving the soul a body obscures the memory. As Plato says "the soul ... is imprisoned in and clinging to the body", and the use of senses clouds the soul, since they are inaccurate. It is only through intellectual contemplation that the soul can be somewhat separated from the body, and in this way thought becomes clearer. In the Phaedo, Plato asserts that it is the job of all philosophers to try to separate the soul from the body, in order to think the clearer. This is why they should shun earthly pleasures, since ëvery pleasure and every pain provides ... another nail to rivet the soul to the body".
A problematic area in relation to the other world of Forms being a physical reality is the idea of Forms of concepts. If there is a physical world of Forms, and all the Forms are totally separate, then that would surely suggest that concepts such as justice would have to exist in a physical form, without recourse to any other Forms. This seems to bring about problems reminiscent of those surrounding primary and secondary qualities. Surely moral concepts and the like would be similar to secondary qualities, unable to exist in isolation, but having to exist in relation to something. That is like you have to have 'a brown table' rather than just 'brown', you have to have 'a just man' rather than merely 'justice'.
There are also problems with Plato's argument for the existence of the soul, it being slightly circular, since he claims that the soul is the Form of life, and that being a Form, is eternal, and also cannot admit its opposite, death, and therefore our soul lives forever. However, his argument for the theory of Forms relies upon the existence and transmigration of the soul. Without the soul, there is no mechanism for us to discover the Forms in their intellectual realm, and thus the theory falters. This minor point is not fatal to the argument, since alternative mechanisms could be postulated, it is just that Plato doesn't, since he sees no need to.
Plato's argument for his theory is twofold. His initial argument is very simple, and yet quite persuasive. He claims that since when we view objects, we realise that they are not the perfect form of that object, we must have some conception of what the perfect Form of the object is. This assumes that we, as imperfect beings, cannot be the creators of a perfect concept, a not unreasonable assumption. Thus, we must have encountered the Form, and he places that meeting in pre-life. The second argument is a little more complex, and much more persuasive. Plato claims that because one can elicit answers to questions that a person has not previously 'known' the answer to, it is innate from birth. He illustrates this in the Meno by questioning a servant about the mathematical problem of doubling the size of a square. He claims that because he is able to get the servant to realise that doubling the side more than doubles the area, that that knowledge is innate. There are several possible counter-arguments to this. The first is purely stylistic, that the questions that Plato asks, through Socrates, are leading questions. From each one it is reasonably obvious what answer is expected, or at least if the last answer given was wrong. Thus when the servant initially claims that doubling the side will double the area, he is asked a series of questions leading to the question Ïs this square then, which is four times as big, its double?" This is obviously nothing to do with recollection, but is really teaching. Having demonstrated that the servant is wrong, he leads him into the correct answer. This may just be a bad example by Plato, but it seems like damning evidence against his theory of recollection if it is the best he can produce. The second argument against this knowledge being innate is that one could say that it is the ability of humans to reason that allowed the servant to derive the true answer. This may seem like just using a different label, but it does mean that there would be no need for innate knowledge, and thus the majority of the theory of forms. One could also postulate reason instead of recollection as a response to the first argument. Having viewed several non-identical instances of 'stick', a person comes to realise that no stick is the perfect stick.
There are three other main arguments against the theory of Forms. First is one that has been already touched upon, the fact that to fully accept the theory, one has to accept the existence of the soul. This means that should one believe that there is no such thing as the soul, or even no form of existence outside of our time in these bodies, then one has to instantly reject half of Plato's theory. One can no longer believe in the postulated mechanism for our knowledge of the Forms, and in fact the conception of another physical place where the Forms exist seems ridiculous. However, the theory can be salvaged by suggesting that there are perhaps not a set of overall Forms, but that each person builds their own Forms. Forms would then be an amalgam of all our data, sensory and otherwise, about an object, or indeed a concept, since there is now no problem in concepts having a physical existence.
Second is one of the side issues that Plato raises. He claims that contemplation of the Forms is 'good', indeed it is perhaps the highest 'good' we can achieve, since it is attempting to separate the soul from the body, and move it up Plato's Line, into the intellectual realm. However, this can lead to some unpleasant conclusions. Since every object and concept must have a Form, violence, crime and torture devices would all have perfect Forms, and the contemplation of these would be 'good'. It seems counterintuitive to suggest that what would be perceived as bad can be considered good. However, a way out of this problem is to note that contemplation of these Forms does not necessarily relate to their acceptance. Indeed, perhaps the understanding of the perfect murder could lead to someone being able to combat or prevent it.
The third argument is one that seems to have totally escaped Plato's notice. He claims that objects are just imperfect copies of the Forms, but provides no mechanism for this to come about. This leaves us with a large hole in the argument, how do objects come to resemble their Forms. In the absence of an explanation, it seems that the theory reverses, Forms resembling the objects, since the objects exist seemingly without needing to rely upon the Forms, but the Forms need the objects to exist. This would be another reason to modify Plato's theory to the idea that we create our own Forms. This is no longer Plato's theory, but is recognisably similar.
It seems therefore that Forms do exist, in a sense. Plato's theory has been found lacking in several aspects, but perhaps he had answers to these, but we do not know what they were. Whatever, through several modifications of his theory, we have been able to give it a firm grounding. While there is room for doubt on the existence of Forms, they do explain how we can recognise non-identical objects as falling into the same group. Any objections would have to postulate a new mechanism for this. The modified theory also returns to humans the power of reason, such as had been taken away by Plato, dismissing it as recollection. This was perhaps one of the more unpopular aspects of the theory, so removing it should placate some of those who object to the theory on the grounds that it demeans the power of the mind.
J. Cottingham, Western Philosophy: An Anthology (Oxford: Blackwell Publishers, 1997) Plato, The Republic (London: Penguin Classics, 1987) Plato (Trans. G.M.A.Grube), Five Dialogues (Indianapolis: Hackett Publishing Co., 1981) B. Russell, History of Western Philosophy (London: Routledge, 1995)