How do I know that I know?

The eponymous character of the Meno introduces the Debater’s Argument after suffering various setbacks in the pursuit of virtue.  As a solution to this apparent paradox, Plato offers the theory of recollection.  Plato did not introduce the Debater’s Argument to philosophy, and his solution was not the only one proffered.  In Posterior Analytics, Aristotle rejects Plato’s solution as well as another popular solution before supplying his own.  Of these, Aristotle’s solution best proves this argument false.

Plato presents the Debater’s Argument in this manner:

“How will you look for it, Socrates, when you do not know at all what it is?  How will you aim to search for something you do not know at all?  If you should meet with it, how will you know that this is the thing that you did not know?

I know what you want to so, Meno.  Do you realize what a debater’s argument you are bringing up, that a man cannot search either for what he knows or for what he does not know?  He cannot search for what he knows—since he knows it, there is no need to search—nor for what he does not know, for he does not know what to look for.”  (Meno, 80d)

Socrates responds with Plato’s famous theory of recollection because he cannot accept the implications of this argument’s conclusion, which would make men idle and fainthearted.  He disproves the first premise by challenging the assumption that man cannot learn what he already knows.  He states that the immortality of the soul provides it with the knowledge of all things, and that the teacher merely aids the learner in the recollection of this knowledge.  This theory of recollection enables Plato to reject the Debater’s Argument and preserve the validity of the philosophic life.

The theory of recollection has several advantages at first glance.  As Socrates demonstrates immediately following his revelation of the theory, one can teach another without ever giving him knowledge.  He guides a slave boy to know the square root of eight through a series of questions, and Meno himself admits that the boy had never learned geometry.  If the knowledge had not been given to the slave boy, he must have already had it without being aware of it.  This theory also recognizes that one cannot come to know what he does not already know, for the man who recollects something, does know it without knowing that he knows it.  For all this, the theory of recollection seems an adequate solution to the Debater’s Argument.

As strong as Plato’s theory may seem, a close examination reveals many weaknesses.  The strongest obstacle lies in its reliance on an existence for the soul before human life.  As Socrates says, “during the time he exists and is not a human being he will have true opinions which, when stirred by questioning, become knowledge” (Meno, 76a).  Even with this objection eliminated, or with reincarnation accepted, the theory of recollection does not provide an ultimate source of knowledge; it merely states that at some time in the life of the soul, it learns.  When Plato sees that some knowledge exists in man, seemingly source-less, he attributes it to a priori knowledge; as Alpharabius realizes, man acquires some principles without any awareness and because of this he does not recognize their empirical character (Black 2008, 22).  In a similar manner, the man born to an enslaved father will not know of his family’s past freedom and consider his family perpetually enslaved.  Aristotle continues in this manner in the Prior Analytics.  He states, “along with the process of being led to see the general principle [man] receives a knowledge of the particulars, by an act (as it were) of recognition (67a22).  Here he suggests that Plato confused the instantaneous syllogistic process following sensory knowledge with recollection (Gifford 1999, 13).  Plato alone, however, did not possess the only solution to the Debater’s Argument.

In the Posterior Analytics, Aristotle describes a solution to the Debater’s Argument.  Some men proposed that when someone says that he knows something, he does not mean that he knows it absolutely, but that he knows it of every instance of which he is aware.  Thus the man who knows that every pair is even does not know that every pair is even, but that every pair which is knows to be a pair is even.  Aristotle has little patience for this solution.  He answers that the man declaring that he knows by a demonstration, declares that he knows absolutely, not that he knows in part.  As Thomas observes, “in the premises no proposition concerning number or straight line is stated with the addition, ‘which you know,’ but it is stated of all without qualification” (Expositio Libri Posteriorum Analyticorum, lib. 1 l. 3 n. 5).  It remains for Aristotle to answer the question in his own manner.

Aristotle proves in the Posterior Analytics that innate knowledge is impossible.  To do this, he discusses demonstrable knowledge and proves that it is the most exact and sure type of knowledge which a man may acquire.  Innate knowledge, he says, would be more exact than demonstrable knowledge.  Such a thing is impossible due to the nature of demonstrable knowledge.  The man who possesses demonstrable knowledge has knowledge without qualification, or absolute knowledge.  This man knows the explanation behind a thing and that it is necessarily so.  This type of knowing must be true knowledge, for anyone who believes that he has the truth thinks in this manner.  Besides truth, demonstrable knowledge has five other characteristics; it is “primary, immediate, better known than, prior to, and explanatory of the conclusion” (71b21-22).  Each of these characteristics aids Aristotle in the disproval of the Debater’s Argument.

That demonstrable knowledge must be true hardly needs to be proven; one cannot know something without qualification if that thing does not exist.  It must derive from primary premises and be immediate because anything else than primary and immediate premises would have a demonstration of its own.  An immediate and primary premise needs so explanation; it is something natural, which as Aristotle says in the Physics, is so evident that the man who needs to prove it has “an inability to discriminate what is known because of itself from what is not” (193a6).  It must be explanatory because no one considers a thing known if he does not have its explanation.  To explain something, the knowledge must be prior to the thing by nature (to say that something is prior by nature means that it had to exist before it could be perceived).  The knowledge must be better known by nature than its conclusion because one always has a better understanding of causes than the effects.  With demonstrable knowledge possessing all these characteristics, one sees that demonstrable knowledge is that of which the knower is completely convinced.

Aristotle continues to discuss how demonstrable knowledge is necessary.  Something is necessary when it belongs in every case, of its own right, and universally.  To belong in every case means that it “belongs not merely in some cases, or at some times, as opposed to others” (Posterior Analytics, 73a29-30) but in every case.  To belong of its own right, a thing must belong to its subject in what it is, as line belongs to triangle or point to line.  It may also contain the subject in its definition while belonging to the same subject, as straight and curved belong to line.  To be universal, the knowledge must be applicable to anything of which it can be said.  Thus, demonstrable knowledge is necessary.

As said above, Aristotle considers it absurd to believe that man possesses innate knowledge, for it would be a type of knowledge of which the knower is unaware, but more exact than demonstration (Posterior Analytics, 99b27-29) and demonstrable knowledge is such that man cannot possess it without being aware of it, as the reasons given above have proven.  One can scarcely admit that one who possesses demonstrable knowledge will be unaware; each of the characteristics given above implies one’s awareness of their possession.  The opposite cannot be true, that man acquires knowledge without prior knowledge, for that has also been proven impossible.  With Plato’s theory of innate knowledge proven false, his theory of recollection can no longer stand.

Aristotle gives his solution to the Debater’s Argument at the beginning of the Posterior Analytics.  He observes that one can come to know what he already knows, if he comes to know it in a different manner than he already knows.  It is only absurd to say that one seeks to know something in the same way as he already knows it, as the man literate in English learning to read English.  In this manner, he agrees and disagrees with Plato that one cannot know learn something if he does not already know it.

The question remains as to the nature of learning, as to what man comes to know.  With absolute knowledge and absolute ignorance proven impossible, something must remain, for man certainly learns.  Until the nature of learning has been uncovered, any solution to the Debater’s Argument lacks teeth, for the conclusion of the Debater’s Argument is that man cannot learn, and while Plato’s theory has its faults it does solve the argument.  As Professor Barnes says, Aristotle does not deny that the learner does not know what he seeks (Barnes 1994, 88).  He knows it; he does not know it.  Thomas likens it to potency (Expositio , lib. 1 l. 3 n. 5).  Aristotle calls this “potential knowledge.”

In the Physics, Aristotle defines a potential thing.  A potential thing does not exist in act, but only in potency.  Potential knowledge exists just as matter exists.  Unformed matter never exists apart from form, but it still exists.  In a similar way, unknown knowledge never exists until it is formed by some formative principle.  In man, this formative principle is the agent intellect while the unformed knowledge is the passive intellect.  The passive intellect is the part of man which may know everything, but actually knows something.  To come to know something, the agent intellect must extract the universal from a thing already perceived by the senses—and thus known in a particular sense—and impress it upon the passive intellect, which comes to know in a universal sense.  In this manner, the man who comes to know already knew it from sensation, but never had it impressed upon his passive intellect.  Thus Aristotle may be said to have solved the Debater’s Argument by answering that when man comes to know, it is not from actual knowledge or actual ignorance, but from potential knowledge.  If it is from potential knowledge, then he knows particularly and does not know absolutely while the thing known still exists particularly.

In addition to these proofs, Aristotle’s solution also better explains Socrates’ example from the Meno.  The slave in question already knows potentially the square root of eight.  At the same time, he does not know it, as he shows when he gives a mistaken answer.  If actual knowledge of the square root existed in the slave, he would never have erred, for innate knowledge would be true and impossible to deceive.  If the knowledge were demonstrable, he would not have answered falsely due to its characteristics.  He knows the square root of eight potentially.  Socrates’ questions provide him with particular things from which he gains sense knowledge of the square root in a particular instance.  When enough of these particular things have been presented to the slave, he makes the logical conclusion about the individual instance of the square root of eight along with a simultaneous conclusion about the nature of all square roots of eight, to which Plato makes the conclusion noted earlier by Professor  Gifford, that Plato confuses instant logical conclusions with innate knowledge.  Thus one perceives that Aristotle’s solution to the Debater’s Argument not only solves it, but explains Plato’s example better than his own theory.

From these examples, it is evident that Aristotle and Plato have provided the two main solutions to the Debater’s Argument.  Plato says that man has innate knowledge acquired during a time before life and in this way knows without knowing that he knows.  Aristotle holds that man has potential, but not actual, knowledge of things and thus knows without knowing that he knows.  The third solution, that man does not state his absolute knowledge of things by his statement of knowledge, easily fails.  Of the two remaining, Aristotle has the best.  Not only does his solution provide an ultimate source of knowledge in material things, not only does it explain Plato’s example better than Plato, but it also renders Plato’s theory of innate knowledge impossible to hold.  In any estimation, the combatant who renders his opponent immobile attains the crown, and thus does Aristotle.


Barnes, Jonathan, trans. 1994.  Posterior Analytics.  2nd ed. Clarendon Aristotle Series.  Oxford: New York: Clarendon Press.

Black, Deborah.  2008. “Al-Fārābī on Meno’s Paradox.”  In In the Age of al-Fārābī: Arabic Philosophy in the Fourth/Tenth Century, edited by Peter Adamson, 15–34.  London: Warburg Institute.

Cohen, S. Marc, Patricia Curd, and C. D. C. Reeve.  2011.  Readings in Ancient Greek Philosophy: From Thales to Aristotle.  4th ed.  Indianapolis: Hackett.

Gifford, Mark.  1999. “Aristotle on Platonic Recollection and the Paradox of Knowing Universals: Prior Analytics B.21 67a8-30.”  Phronesis XLIV, no I (February): 1–29.

Kenny, Joseph, ed. 2013.  Expositio Libri Posteriorum Analyticorum.  Translated by Fabian R. Larcher.  Accessed November 30, 2013.

McKeon, Richard, ed. 2001.  The Basic Works of Aristotle.  The Modern Library Classics.  New York: Modern Library.

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