Here Sokrates makes out a good case against the answer in its present wording. But we may fairly doubt whether those who affirmed the matter of knowledge to consist in the facts of sense, ever meant to exclude memory. They meant probably the facts of sense both as perceived and as remembered; though the wording cited by Plato does not strictly include so much. Besides, we must recollect, that Plato includes in the meaning of the word Knowledge or Cognition an idea of perfect infallibility: distinguishing it generically from the highest form of opinion. But memory is a fallible process: sometimes quite trustworthy — under other circumstances, not so. Accordingly, memory, in a general sense, cannot be put on a level with present perception, nor said to generate what Plato calls knowledge.
Argument from the analogy of seeing and not seeing at the same time .
The next argument of Plato is as follows. You can see, and not see, the same thing at the same time: for you may close one of your eyes, and look only with the other. But it is impossible to know a thing, and not to know it at the same time. Therefore to know is not the same as to see.[89]
[89] Plato, Theætêt. p. 165 B.
This argument is proclaimed by Plato as a terrible puzzle, leaving no escape.[90] Perhaps he meant to speak ironically. In reality, this puzzle is nothing but a false inference deduced from a false premiss. The inference is false, because if we grant the premiss, that it is possible both to see a thing, and not to see it, at the same time — there is no reason why it should not also be possible to know a thing, and not to know it, at the same time. Moreover, the premiss is also false in the ordinary sense which the words bear: and not merely false, but logically impossible, as a sin against the maxim of contradiction. Plato procures it from a true premiss, by omitting an essential qualification. I see an object with my open eye: I do not see it with my closed eye. From this double proposition, alike intelligible and true, Plato thinks himself authorised to discard the qualification, and to tell me that I see a thing and do not see it — passing à dicto secundum quid ad dictum simpliciter. This is the same liberty which he took with the Protagorean doctrine. Protagoras having said — “Every thing which any man believes is true to that man” — Plato reasons against him as if he had said — “Every thing which any man believes is true”.
[90] Plato, Theætêt. p. 165 B. τὸ δεινότατον ἐρώτημα — ἀφύκτῳ ἐρωτήματι, &c.
Mr. Campbell observes upon this passage:— “Perhaps there is here a trace of the spirit which was afterwards developed in the sophisms of Eubulidês”. Stallbaum, while acknowledging the many subtleties of Sokrates in this dialogue, complains that other commentators make the ridiculous mistake (“errore perquam ridiculo”) of accepting all the reasoning of Sokrates as seriously meant, whereas much of it (he says) is mere mockery and sarcasm, intended to retort upon the Sophists their own argumentative tricks and quibbles. — “Itaquè sæpe per petulantiam quandam argutiis indulget (Socrates), quibus isti haudquaquam abstinebant: sæpè ex adversariorum mente disputat, sed ita tamen disputat, ut eos suis ipsorum capiat laqueis; sæpè denique in disputando iisdem artificiis utitur, quibus illi uti consueverant, sicuti etiam in Menone, Cratylo, Euthydemo, fieri meminimus”. (Stallbaum, Proleg. ad Theæt. pp. 12-13, 22-29).
Stallbaum pushes this general principle so far as to contend that the simile of the waxen tablet (p. 191 C), and that of the pigeon-house (p. 200 C), are doctrines of opponents, which Sokrates pretends to adopt with a view to hold them up to ridicule.
I do not concur in this opinion of Stallbaum, which he reproduces in commenting on many other dialogues, and especially on the Kratylus, for the purpose of exonerating Plato from the reproach of bad reasoning and bad etymology, at the cost of opponents “inauditi et indefensi”. I see no ground for believing that Plato meant to bring forward these arguments as paralogisms obviously and ridiculously silly. He produced them, in my judgment, as suitable items in a dialogue of search: plausible to a certain extent, admitting both of being supported and opposed, and necessary to be presented to those who wish to know a question in all its bearings.
Again, argues Plato,[91] you cannot say — I know sharply, dimly, near, far, &c. — but you may properly say, I see sharply, dimly, near, far, &c.: another reason to show that knowledge and sensible perception are not the same. After a digression of some length directed against the disciples of Herakleitus — (partly to expose their fundamental doctrine that every thing was in flux and movement, partly to satirise their irrational procedure in evading argumentative debate, and in giving nothing but a tissue of mystical riddles one after another),[92] Sokrates returns back to the same debate, and produces more serious arguments, as follows:—