Even though Plato pursues the problem of the nature of knowledge in many of his dialogues, nowhere does he develop an exhaustive theory of knowledge. He principally dismisses experience as the source of certain knowledge, and indicates education and diligent intellectual exercise as the method of attaining the knowledge of the Forms.

Ontology and Theory of Knowledge

Questions on knowledge theory are often raised throughout the Platonic corpus. That said, no particular dialogue takes up an exhaustive illustration of the philosopher's knowledge theory. Although, the subject of the Theaetetus is the nature of knowledge, the discussion boils down to the refutation of empiricism - and concludes in aporia over the nature of knowledge. It is also clear that Plato never subscribed to the thesis that experience can provide true knowledge; this is a position that the philosopher ascribes to the sophist Protagoras.

Only the knowledge of purely intelligible Forms is, for Plato, equal to certain knowledge. The existence of the Forms is an unexceptionable premise at work throughout the platonic corpus; it is a "basic thesis" (a hypothesis) which is postulated but not proven. Nevertheless, it is worth noting that, when Plato attempts at "demonstrating" the existence of the Forms, he adduces an argument from the field of epistemology.

"So here’s how I cast my own vote: If understanding and true opinion are distinct, then these “by themselves” things definitely exist—these Forms, the objects not of our sense perception, but of our understanding only. But if—as some people think—true opinion does not differ in any way from understanding, then all the things we perceive through our bodily senses must be assumed to be the most stable things there are. But we do have to speak of understanding and true opinion as distinct, of course, because we can come to have one without the other, andthe one is not like the other" (Timaeus 51d-e).
Socratic Dialogues

It is certain that, with regards to Plato's view on knowledge, we cannot draw sufficient information from his early dialogues, where Socrates proclaims, self-complacently, to "know that I know nothing". In these dialogues, Socrates comes out with an innate ability to conceive moral truths - an ability that sets him apart from his adversaries, the Sophists. However, this ability is not predicated on intellectual training, nor does it extend to matters beyond morality. Thus, if we take (the well beaten path) that Plato gradually moves away from Socrates -towards a more positive pronunciation of basic philosophical theses- we confirm the requirement for an unshakable foundation upon which true knowledge can rear.

Knowledge as 'Recollection'

In Meno and Phaedo, Plato propounds the distinction between a mortal body and an immortal soul. By adopting the language of the mysteries, the philosopher seems to endorse the doctrine of reincarnation, according to which the soul is consecutively incarnated in different bodies, and lives many lives. Nevertheless, the way Plato introduces the belief in reincarnation shows that his intention is not to affirm widespread mystic doctrines, but to raise questions regarding the nature of knowledge. The paradox put forward in the Meno refers precisely to the question of knowing: if we already know something, then there is no reason for us to learn it; on the other hand, if we had not known it already, how would we know that we learned it? To answer the paradox Plato adduces a version of the doctrine of reincarnation: what we learn, we do not learn it ab initio, but through recollection.

Given that the soul survives the death of the body, she becomes eligible to contact the eternal Forms. This knowledge is obliterated when the soul enters a new body. However, under the right conditions, the soul can retrieve the knowledge it had acquired - and, therefore, true knowledge is in essence a "recollection". In this context, it is appropriate to ask whether Plato, the rationalist, adheres to the -obviously arbitrary- doctrine of reincarnation, or not. Is the allegorical trope of the myth resolute for a tough philosophical problem? The answer should not be precipitated, for Plato, before all else, is an author of remarkable skills. At any rate, those who wish to purge platonic philosophy of any arbitrary, religious-esque believes can be lent support by the argument that the philosopher uses the dogma of reincarnation as an allegory. Its purpose is to flesh out the conviction that human kind is endowed with innate rationality and the possibility of knowledge. This conviction anticipates the kind of knowledge that modern philosophy named 'a priori', and which is common in every rationalist epistemology.

The allegory of the "Line" in the Republic

None of Plato's late texts prompts any doubt to the possibility of valid knowledge. No matter if the course to knowledge is not clearly described, or if it is rendered accessible only to an ingenious elite, knowledge of the Forms, that is, true knowledge, remains graspable.

In the 6th book of the Republic, Plato elaborates on beings and knowledge by appealing to the image of a line, which is divided into two unequal sections. The wider section of the line corresponds to the intelligible beings, whereas the shorter to the sensible objects - knowledge of the former yields belief, and of the latter truth. Each section is further dichotomized into two unequal parts; thus, sensible objects are divided into physical objects and their images, while the intelligible beings into the Forms and the mathematical objects. The corresponding cognitive operations are "imagination" (eikasia) for images, "belief" (pistis) for sensible objects, "thought" (dianoia) for mathematics, and "understanding" (noēsis) for Forms. By means of the parable of the Divided Line, Plato illustrates a cognitive course that sets out with the delineation of the images that belong to the sensible objects, moves onto the sensible description of existing beings, advances to the rational elaboration of the mathematical concepts, and culminates to the understanding of the Forms. By way of analogy, Plato designs the curriculum of his ideal city: just a few among the citizens will be selected for a 10-year study program in mathematical science, and even less, the philosophers-kings, will achieve the knowledge of the Forms.

So the path to true knowledge is that of long-term, rigorous education into progressively advancing subjects. This view is not at odds with the claims vented in the Phaedo, where philosophy is called "training for death" (67d-e): appropriate education enables the power of the student to "recollect" whatever his soul cognized before its embodiment. The path to true knowledge can be also put in the perspective of joining in love (eros) as it is propounded in the Symposium. According to Plato, love is a "philosophical" motivation, which drives man through ascending stages to the understanding of the Forms. That said, the final stage of this cognitive (as well as loving) process remains obscure. In two cases -in the Symposium (210e) and in the Seventh Letter (341cd)- Plato uses the adjective suddenly to describe the cognitive lip of the soul unto the understanding of the Forms.

In any case, an interpretation of this sudden illumination as an irrational epiphany would be misleading. Plato considers that the conditions for the successful ascension unto the final stage of knowledge are: the natural qualifications of man, the rigorous intellectual effort, and the long-term study under an appropriate mentor. The understanding of the Forms (or of the superior Form of the Good, or the One) figures as an intellectual transcendence; this transcendence, however, occurs only to him who has prepared himself in the right way, and, furthermore, is not a final step. Philosophy remains the "love for wisdom", that is, an interminable progress in wisdom; for it is god alone who can be properly called wise (Phaedrus 278d).

Author: Vassilis Kalfas
  • Cooper, J. ed. Plato: Complete Works. Indianapolis, 1997.
  • Fine, G. ed. Plato 1: Metaphysics and Epistemology. Oxford, 1999.
  • Kraut, R. "Plato." Zalta, E.N ed. Stanford Encyclopeidia of Philosophy http://plato.stanford.edu/entries/plato. 2013.
  • White, N. P. Plato on Knowledge and Reality. Indianapolis, 1976.
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