Plato’s theory of the forms is developed in several different places.  Most famously, Plato describes the world of the forms and how it relates to the world of human experience through his Allegory of the Cave, found in Book VII of The Republic.  Here, Plato describes how human beings are like prisoners, trapped by the cave of sense-experience and how it is possible to escape – through reason – coming to the realization that Ultimate Reality is metaphysical in the world of the “forms.”  Elsewhere, Plato used the analogies of the Sun and the Divided Line to explain his theory differently, but nowhere did Plato provide any systematic account of or argument for the theory.  It seems that for Plato, a form is the essence of something, what makes it what it is.  It is what enables us to recognize what something we encounter is and what makes it possible to judge whether it is a good (or bad) example of its type.  The word “form” is also used to refer to the model which a mason used to ensure all his carvings were the same; it is the blueprint, the type, the design.  Unlike things that we encounter through our senses, the form is unchanging, perfect, complete and it is this which makes it more “real” than physical things in the ever-changing partial and imperfect world of the senses.  “The Platonic idealist,” said George Santayana, “is the man by nature so wedded to perfection that he sees in everything not the reality but the faultless ideal which the reality misses and suggests.”  However, Plato is not clear how many forms exist – is there a form of everything or only a few or even one ultimate form?  Further, Plato fails to argue for his position, preferring to describe a worldview using allegories and analogies.  Julia Annas observed that

“Plato not only has no word for “theory”; he nowhere in his dialogues has an extended discussion of Forms in which he pulls together the different lines of thought about them and tries to assess the needs they meet and whether they succeed in meeting them” An Introduction to Plato’s Republic, p217 

While it has been enormously influential and while it does have intuitive appeal, Plato’s theory of the forms is unconvincing because of this lack of coherent argument. 

Further, nothing much seems to separate Plato’s theory of the forms from speculation.  As Aristotle pointed out in Metaphysics Book 1,

“… If, then, a man has the theory without the experience, and recognizes the universal but does not know the individual included in this, he will often fail” 

Plato’s focus on reason as the only source of wisdom – and his belief that sense-experience could actually mislead people – means that his theory is not supported by any observable evidence.  There is no way to see, hear, smell, taste or touch the forms and, while Plato would suggest that this is just the point, what then distinguishes Plato’s theory from baseless speculation?  Take flat-earth theory or young earth creationism.  It is, as Bertrand Russell pointed out, impossible to disprove the idea that the universe was created with all the appearance of age 5 minutes ago… or indeed something over 6000 years ago in a period of 6 days.  While this would raise serious questions over His goodness, a mischievous creator could well have planted “fossils” in rock strata and rigged the moon-landings to deceive credulous scientists and identify those few with unshakable blind faith in what goes against the evidence to elevate to their eternal reward.   In the same way – in the absence of the sort of freak-chance-escape Plato describes in his allegory – it is impossible to disprove Plato’s proposal that we exist in a shadowy prison of the senses and that ultimate reality exists beyond in some forever-unattainable world of the forms.  Plato even acknowledges how the revelation of such news would be received by those still in the cave. In the absence of supporting evidence – and when Plato’s theory seems to call for an active suspension of disbelief – how is it more credible than flat-earth theory or young earth creationism?  In this way as well, Plato’s theory of the forms is unconvincing. 

Aristotle also criticized Plato for being inconsistent in his speculations; must there me a form of the yellow pencil with blunt lead and the form of my half-drunk cup of tea?  Why shouldn’t there be a form of evil, sin etc?  Also, what prevents there being an infinite regress of forms?  Plato himself acknowledged this as a problem for his theory in the dialogue Parmenides – in what Bertrand Russell in his “History of Western Philosophy” described as “one of the most remarkable cases in history of self-criticism”.  Here,Plato seems to suggest that where things display a particular quality, such as greatness, there must be a form through which we perceive it to have this quality, a form of greatness through which to appreciate its greatness. The Form of greatness must be unchangeably perfect, supremely great as an example of greatness, but if the form of greatness is itself great, and thereby an example of greatness, there must be a separate form through which we perceive the greatness of the form of greatness… and another form through which we perceive the greatness of the form of the form of greatness and so on to infinity.  A similar problem was highlighted by Pelletier and Zalta in their 2003 article “How to Say Goodbye to the Third Man.”  They use the example of ‘Loveliness’: If all things lovely become such and acquire their loveliness by virtue of partaking in the respective Form of Loveliness, then they must themselves be ‘like’ that Form. Following from the “symmetry of likeness” it can be said that the Form must, then, be ‘like’ the objects which partake in it. If this is true, the Form of Loveliness and the lovely objects must resemble one another by virtue of a further Form, of which they both partake. This, again, continues ad infinitum, creating Forms interminably to explain the likeness of the Form to its instantiations.  Plato had no satisfactory answer to these problems, as Aristotle made clear in the Metaphysics, using the example of the third man.  In this way Plato’s theory of the forms is philosophically unconvincing. 

Nevertheless, George P Simmonds argues that Plato’s theory of the forms could survive Aristotle’s criticisms.  He points out that

“the Third Man Argument relies too heavily on assumptions generated by a swift and unsophisticated interpretation of Plato’s thinking.”

And goes on to point out that far from being a sign that Plato was abandoning his theory of the forms, Plato’s inclusion of this line of criticism in Parmenides points to Plato’s confidence in his theory and in his students’ ability to see the weakness of this line of criticism. In particular, Simmonds takes issue with Aristotle’s assumption that Plato’s argument with respect of particular things also applies to the forms. Just because the greatness of things in the world necessitates the existence of a form of greatness through which we perceive that greatness, does not mean that the same applies in the world of the forms. Having said that, Simmonds’ defence of Plato fails to justify Plato in being inconsistent in his treatment of the forms or for failing to provide a systematic defence of his own work, so it goes only so far in making Plato’s theory more convincing.  

In conclusion, Plato’s theory of the forms is unconvincing because Plato fails to give a clear, consistent account of his theory.  While this conclusion it may be a little unfair to Plato, given that he lived nearly 2500 years ago and given the fragmentary nature of our records of his work, his theory is frequently presented as a philosophical argument today, and in this context it must be evaluated as such. Further, just because Plato’s theory of the forms is unconvincing does not mean it is not worthy of serious study and development into what may be far more convincing theories.  Indeed, Plato’s belief that ultimate reality is metaphysical is gaining popularity today through theories like the holographic universe and the simulated universe. 

Bibliography

• Plato, Republic Books 5, 6, 7 and 10
• Aristotle, Metaphysics Book 1
• Julia Annas “An Introduction to Plato’s Republic” Chapters 9 & 10
• George P Simmonds “The Third Man Argument” in Philosophy News, January 2018 https://www.philosophynews.com/post/2014/03/10/The-Third-Man-Argument-Parts-3-4.aspx
• Pelletier and Zalta “How to Say Goodbye to the Third Man.” (2003)