The Genesis and Motivation for Plato’s Theory of Forms: Summary and Comments on Harold Cherniss’ “The Philosophical Economy of the Theory of Ideas”

Harold Cherniss’ “The Philosophical Economy of the Theory of Ideas”: Summary and Comments  

Pdf of Cherniss’ article available here:

Key terms: A Priori, Recollection Argument, Eristic Argument, Hypothesis, Early Dialogues, Middle Dialogues, Fifth Century, Theory of Forms

Topics: The hypothetical method as leading to the theory of forms (the intellectual genesis of the theory of forms), the 5th Century background to the development of the hypothetical method, the importance of and need for an absolute ethical standard/underivative standard of reference,  the result of the “dialogues of search,” the eristic argument in the Meno, the recollection argument, teaching and knowing, the epistemological necessity of the theory of ideas


  1. Introduction
  2. Cherniss’ Account of the Fifth Century Background to Plato’s Discussion of Ethics in the Early and Middle Dialogues
  3. Plato and Relativism/Plato’s Motivation for Developing his Theory of Forms
  4. The Eristic Argument
  5. Comment: Text and Formalization of the Argument
  6. Comment: Evaluation
  7. Plato’s Response to the Eristic Paradox: the Recollection Theory of Knowledge
  8. Final Comments and Further Remarks on the Application of the Eristic Argument and Recollection Theory to the Contemporary Scene


Harold Cherniss’ “Philosophical Theory of Ideas,” originally published in 1936 in the American Journal of Philology, concerns the genesis of Plato’s theory of Ideas or Forms, its rationale, and Plato’s own discussion of its attendant epistemological difficulties. The article may be divided into two parts, one that concerns the genesis of the theory in relation to ethics in the early and middle dialogues, and a second part that concerns epistemological questions in Plato’s later dialogues. The following will discuss the first part of the article (pp. 445-448).

Cherniss’ article has the special merit of providing a clear explanation for why the theory of Ideas or Forms was developed at all-a discussion that may well be very important for a proper appreciation and enjoyment of their content. Cherniss locates the primary texts for his theory within the dialectical battlefield of the Meno, specifically in two arguments labelled the “eristic argument” given by Meno (Socrates’ opponent in the debate) and Socrates’ response, an argument that produced his theory of “recollection.” After a brief discussion of the fifth century background to the discussion and the development of a criterion for an ethical absolute, the stage is set for the discussion in the Meno. The stage is then set for a summary of what Plato hoped to show and for further consideration of its significance.  

Cherniss’ Account of the Fifth Century Background

Plato’s development of his theory of Ideas or Forms grew out of his concern with ethical absolutes.  Cherniss describes Plato as having been concern to defend the possibility of such absolutes against a tide of relativism that had surfaced in the 5th century. Cherniss refers to such 5th century sources as the “dissoi logoi,” which he describes as discussing the relativity of such concepts as good and evil, the just and unjust, “fair” vs. “foul,” and even the possibility of teaching virtue (Cherniss 446). A further source is a papyrus fragment attributed to Antiphon the Sophist which Cherniss reads as contrasting conventional and natural justice, where conventional justice is “adventitious” and natural justice is simply what is “truly advantageous to each individual.  Those familiar with the Platonic dialogues will, of course, recognize these points of debate as their main themes.  The fact that they were so prominent as themes in the dialogues gives further evidence of the influence they likely had upon Plato.  

Plato and the Relativists/Plato’s Motivation for Developing the Theory of Forms

In seeking to contest the influence of these fifth century sources, Cherniss describes Plato as having recognized that an independent measure of goodness, justice, etc. would be necessary if he was to succeed.  Cherniss, considers that the early dialogues provide clear enough evidence of this point to venture to remark that the point ought not to be labored (Cherniss 447). Socrates does, in fact, repeatedly lead his interlocutors back to the methodological aim of discovering what justice, piety, love, etc. themselves are as opposed to their particular instances of them. Using individual examples of goodness or justice as standards of goodness and justice merely leads back into the trap of relativism: to do so is merely to “measure individuals against one another” leaving us without an independent standard for determining what makes some things, for example, just while others are unjust, and without a way to determine the similarities and differences among things one might want to classify as just or unjust (Cherniss 447). It might be considered that the refusal to accept particular instances amounts to Socrates’ way of funneling his interlocutor into a non-relative conception of ethical standards even as they fail to arrive at one.   

Thus, we arrive at the first step in the development of what Cherniss sees as Plato’s motivation for the theory of Forms or Ideas: “The possibility of ethical distinctions, then, implies objective differences which can be accounted for only by the hypothesis of objective ideas” (Cherniss 447). The justification for such an hypothesis is that it makes ethical absolutes possible, thereby making the determination of the true nature of justice, goodness, etc. possible; however, the defense and development the theory requires that it face certain epistemological (as opposed to methodological) questions-questions that properly concern knowledge itself as a subject of investigation.

One such question arises in the Meno, where the possibility of knowing such ethical paradigms as the Forms are supposed to represent is raised in the context of a discussion of whether virtue may be taught. After all, can what Socrates is searching for be discovered at all? The question is certainly worth asking. Cherniss comments that “a consistent and practical ethical theory depends upon an adequate epistemology” writing that the discussion of the nature of virtue underway in the Meno demands “a prior determination of the nature of virtue itself” (Cherniss 447-448). The dialogue brings the reader to consider these points when, after failing to give Socrates a satisfactory definition of virtue, he introduces a skeptical paradox designed to show that the search for knowledge is self-defeating in nature.    

The Eristic Argument

Enter the “eristic” argument. When Meno is unable to give a proper definition of virtue, he presents one that one might be recognized as being very much in tune with the skeptical tendencies of Plato’s 5th century adversaries.  It may be expressed concisely as the self-defeating proposition, “It is impossible to search either for the known or for the unknown” (cf. Cherniss 447).

Comment: The Text of the Eristic Argument

Going beyond Cherniss for a moment, It might be said, by way of initial clarification, that, while (a) it defies common sense and even logic to imagine searching for something one already has (since searching seems to imply something that is, at least in some sense, lost); on the other hand, (b) if one has no knowledge of what one is looking for, there is no means of finding it or even of knowing when one has found it (some means of discovery and of proof are equally essential for real  knowledge). Thus, it appears impossible to search either for what one already knows or for what is yet unknown. The Greek text and my own literal translation are placed below for the reader’s convenience.

The Greek text (Meno 80 d-e) may be translated as follows:


καὶ τίνα τρόπον ζητήσεις, ὦ Σώκρατες, τοῦτο ὃ μὴ οἶσθα τὸ παράπαν ὅ τι ἐστίν; ποῖον γὰρ ὧν οὐκ οἶσθα προθέμενος ζητήσεις; ἢ εἰ καὶ ὅτι μάλιστα ἐντύχοις αὐτῷ, πῶς εἴσῃ ὅτι τοῦτό ἐστιν ὃ σὺ οὐκ ᾔδησθα;


And how will you look for something when you do not in any way know what it is?  What sort of thing is it you do not know that you are making the object of your search? Or above all, even if you should find it, how will you know that the former was what you did not know?

Notice that Socrates’ gloss of Meno’s objection is different:


μανθάνω οἷον βούλει λέγειν, ὦ Μένων. ὁρᾷς τοῦτον ὡς ἐριστικὸν λόγον κατάγεις, ὡς οὐκ ἄρα ἔστιν ζητεῖν ἀνθρώπῳ οὔτε ὃ οἶδε οὔτε ὃ μὴ οἶδε; οὔτε γὰρ ἂν ὅ γε οἶδεν ζητοῖ—οἶδεν γάρ, καὶ οὐδὲν δεῖ τῷ γε τοιούτῳ ζητήσεως—οὔτε ὃ μὴ οἶδεν—οὐδὲ γὰρ οἶδεν ὅτι ζητήσει.

I understand what you want to express, Meno.  Do you see what a contentious argument you are introducing, that is it not possible for anyone to inquire either into what he knows or into what he does not know? For he would neither seek what he does, in fact, know-for he [already] knows, and no one goes searching for that kind of thing-nor for what he does not know-since he knows nothing about what he will be looking for.

The gloss given above attempts to capture all the elements. It can be seen, in summary, that once Socrates’ own version of it is added to Meno’s, three basic elements of inquiry are in play: the starting point of an inquiry, the end point, and how one knows when the end has been reached.  These elements might, in turn, be related to Plato’s favorite key epistemological terms: a belief as a starting point, knowing as an end-point, and justification as a way of knowing one’s search is complete.  

[The following may be skipped if the reader is not inclined toward symbolic logic]

The search itself is paradoxical in nature because if one knows beforehand, there is no need to search, but if one doesn’t, one cannot find what one is looking for. It may be expressed succinctly in symbolic form as the proposition

                                                        ~K -> ~F & K -> ~F

where K represents “knowing” and F represents “finding knowledge.” As the formula shows, whether one knows or not, finding knowledge does not occur.  Assuming that one must be in either state (K v ~K), one cannot but help to fall into either side of the dilemma. This may be shown (purely for the reader’s enjoyment as it may happen) as follows:

  1. K V ~K
  2. ~K -> ~F & K -> ~F
  3. Assume K is true, then
  4. ~F
  5. Assume ~K is true
  6. Then ~F
  7. Therefore, K v ~K -> ~F

This amounts to a proof that, if the primary premisses (1 and 2) are true, it is useless to search for knowledge (self-defeating) because one either begins with knowledge or without knowledge-and it is impossible to avoid being either state.  

Comment: Evaluating the Eristic Argument

At this point, the reader may be experiencing a sense of exasperation. It appears that the premise, “We must either know, or not know” creates a false dilemma. The argument seems to overlook the distinction between partial and full knowledge. When the claim is made that in order to search for some x one must “know” x, apparently only the strong sense of knowing is considered. One might both have partial knowledge of what a Red Tailed Deer is, for example, and yet not “know” what it is in the stronger sense of the term. Not initially knowing in the strong sense does not appear to present any difficulty for really knowing what a Red Tailed Deer is later.  

In other words, it appears that the solution is simply to acknowledge that some form of induction or perhaps Aristotelian epagoge (lit. “going up”) is a valid method for arriving at full knowledge of a given thing. Setting aside the regress problem of numerical induction or verification (always another case), perhaps the best way to see why the eristic argument should have been taken seriously is to consider it in the context of an axiomatic model of knowledge.  Suppose we begin with partial knowledge and proceed on that basis: according to an axiomatic model, the partial knowledge we have won’t count as real knowledge until some principle is formulated that secures that what we think we know can really be considered knowledge at all.  We may, in other words, proceed inductively (or by epagoge) on the basis of a belief that we are right-but we might also be quite mistaken in that belief.  Examples of proceeding in the wrong direction on the basis of a false belief are not hard to find in the history of science: alchemy or ether theory in the early 20th century come to mind. In contemporary physics, string theory may or may not take us anywhere.  It is not until partial knowledge, based upon hypothesis or belief, is secured as an axiom that we can claim any real knowledge. That, in turn, leaves in doubt whether our starting point will lead us where we want to go.  

In such a context, really knowing will allow us to deduce whatever consequences we have not already drawn, and thus, to really know them too. Nevertheless, it might be insisted that unless some sort of “way up” involving induction or generalization of some kind is allowed, the search for knowledge really will be impossible. Certainly this is right.  But, by the same token,what the eristic argument points out is right.  It points out a problem with knowledge: we don’t really “know” anything until we know it, making it quite possible that, until we have arrived at a principle/axiom that secures our knowledge as knowledge, we may be mistaken.  In such a case, prior knowledge is vital to the search, inasmuch as it helps us to disregard beliefs that are likely to be false before pursuing them. Without prior knowledge, one might very well wonder how anyone can hope to find what they are looking for without prior knowledge of some kind to guide them.

Meno seems to find himself in such a case.  He believes he knows what virtue is, but his accounts of it, playing the role of axioms in Socrates’ critique, fail to secure his accounts as  knowledge.  They run into contradictions with other things we believe we know, making them appear unreliable-and knowledge, more than belief, ought to be reliable. Moreover, nothing he has said has even appeared to be partially correct, which would seem to leave him at a loss as to how to proceed. When he asks how it is possible to look for something lacking any knowledge of what it is, Meno may be read as having reached a point of exasperation either a) as to how to proceed b) as how to proceed lacking any idea of whether he is heading in the right direction (because he lacks any real knowledge of it) or c) as comprehending the problem of how the two are intertwined.  Socrates does intertwine them, by re-framing his question as the eristic argument formalized above with its apparently self-defeating results. What may be seen now is perhaps the extent to which it is, as representing a genuine problem about the search for knowledge-and at the same time isn’t.  

The Recollection Theory of Knowledge

Whatever possible solutions might be given for the dilemma, Socrates’ response is to hypothesize the “recollection” theory of knowledge.“Recollection” involves a prior direct knowledge of the Forms of things (absolute standards for things such as justice, goodness, virtue, etc.) that were available to known prior to one’s birth. One might alternatively think of such knowledge as “innate,” but Cherniss emphasizes that such knowledge of the Forms or Ideas was “direct” in nature, citing Meno 81 D 4-5 (Cherniss 448). Its application to the eristic argument might be given as follows:

  1. Such innate knowledge would give one a prior knowledge of virtue.
  2. The search, in this case, is for a definition of virtue, which would require a knowledge of its essential nature-a non-relative kind of knowledge of what it truly is.
  3. The eristic argument states that one cannot search either for what one knows or for what one does not know, but (1) presupposes that even the essential nature of virtue actually exists, was directly available, and may be known (in the strong sense of the term).

The way in which these premises lead to a solution might be made more explicit than the way in which Cherniss presents the argument as follows:

  1. Such knowledge has a dual nature that defies the paradoxical/self-defeating nature of the eristic argument: firstly, (1) secures the assumption that a true, non-relative definition of virtue really does exist; secondly, (1) allows for both potential and actual knowledge of that definition. This is illustrated by the example of Socrates helping the slave boy to discover knowledge of geometry within himself.
  2. According to the innate hypothesis (1), it would be possible to search for the definition of virtue because, although one does not know what one is searching for, in another sense there is the potential for it to be discovered since:
    1. One once had actual, direct, prior knowledge of it.  
    2. Finally, the process of acquiring such knowledge can be furthered by the efforts of a figure like Socrates, who can help to “learner” to recall it by giving clues that assist in the recollection process. This same process is sometimes described as Socratic midwifery.

It might be noticed that by posing the argument in this way, an overall coherence emerges among the elements of Cherniss’ depiction of the 5th century background, the motivation Socrates had for developing the recollection hypothesis, and the introduction of the eristic argument and its solution.  

The Recollection Hypothesis and A Priori Knowledge

A further implication is that a priori knowledge appears to be required in the search for genuine knowledge of virtue. Plato does not explore the path of reasoning on the basis of prior knowledge through generalization in order to arrive at full knowledge of virtue. One suspects that Cherniss is on the the right track in taking the relativism of the fifth century to be a foil for the present discussion, since a non-relative answer to the problem of what virtue is could not reliably be deduced from experience, since experience is always bound to the time, place, and circumstances of those who are acquiring it. In that case, any real answer would require a priori knowledge of virtue that does not come from our experience. Innatism is at least a way of meeting that requirement. With the supposition of an innate idea of virtue, it will at least be possible, in theory, to proceed from our experience to a true definition, even if that search is not carried out in the dialogue. The recollection argument attempts to provide some basis for such knowledge, which, if the paradox is taken seriously, appears to be necessary for any knowledge-a result which appears to have motivated the theory of Forms.

Final Comments and Further Remarks on Contemporary Application  

In sum, Cherniss’ basic position regarding the progression from the early to middle dialogues is that they can be read together as laying the groundwork and finding a solution to the problem of ethical relativism. What is at stake is that unless some solution to the eristic paradox is given, we must “surrender all possibility of considering ethical problems” (Cherniss 448). Unless some solution can be offered, the relativists have the upper hand and morality is ultimately a matter of custom or persuasion. But the even more serious result is that without some means of acquiring a priori knowledge, even the attempt to discover a non-relativistic way of knowing is doomed to failure.

The supposition of such hypotheses as the recollection theory requires, namely, that we have an immortal soul and that it, in some sense, exists in a “realm” wherein it may acquire direct knowledge of the Forms, may well appear extravagant to contemporary readers. These additional hypotheses might even seem to fatally weaken Plato’s argument; nevertheless, together, they do at least provide a working solution to the problem of a priori knowledge developed thousands of years before Kant’s approach to the same problem and the development of modern genetics. But finally, through Cherniss’ analysis, the eristic argument and its response had three further results for the progress of Plato’s dialogues: (a) as providing a motive for Plato’s discussion of the soul; (b) as a solution to the problem of ethical relativism; and (c) as foundational material for understanding the theory of Forms and its development. Finally, (d) it may be considered that problems the eristic argument raises have led to many of the “perennial” problems of philosophy.

The study of the eristic problem helps illuminate when, where, and why innatism might become necessary as a hypothesis: when the foundations for knowledge, whether universal or absolute enter into our consideration; where the problem of discovering a foundation for our knowledge prior to our everyday experience comes into view, and because, unless it is taken seriously, no other explanation for universal knowledge can be found. Are there other ways to satisfactorily oppose ethical relativism? Is there any other way to approach the problem of absolute knowledge? At the very least, because of its preliminary nature, it seems easy to conclude that the problem of a priori knowledge can be ranked as a meta-ethical question.  

Chomsky’s hypothesis of a universal grammar and Kant’s hypothesis of a set of ultimate mental categories provide two applications. In the case of Chomsky’s “universal grammar,” the problem is not so much related to the problem of absolute knowledge but to an absolute way of processing language, which is encoded in our DNA. If correct, the hypothesis would account for our ability to learn and master language use more easily than we otherwise would be able to. The same attempt to discover a foundation for a universal way of knowing (as opposed to theorizing for specific content) may be seen in the Kantian approach to cognition.  In either case, a point was reached where empirical investigation gave way to supposition and hypothesis.  That point, in each case, was reached when an evident fact could not be directly explained by empirical means.

Whatever course research takes, it begins with hypotheses, some of which are of sufficient generality that they may serve to direct it. The eristic problem and Plato’s solution impact investigations directly where the search for knowledge is required to reflect upon itself, its ultimate directives, and foundations. It would seem that if the apparent result of the eristic problem is taken seriously, a priori knowledge will always be necessary as a foundation for empirical, scientific knowledge.    

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