Thus far in the Theaetetus Socrates, Theodorus and Theaetetus have begun to discuss the nature of knowledge, discussing the Protagorean (and simplistic) ‘man is the measure’ tagline as a prompt to their first candidate: perceiving is knowledge.[1]  What does Socrates mean, or more properly, what does he take Theaetetus to have accepted, by “perceiving is knowledge?”  One thoughtful and easily producible experiment on this thesis is offered by Socrates at 165a, to which I will now turn.

 Socrates: In fact I say this is the most incredible question, and I think it is something like this: is it possible for the same man to know what he knows and not to know what he knows?

 

Theodorus: What then do we reply, Theaetetus?

 

Theaetetus: It is impossible, I think.

 

Socrates: It is not impossible, if you make seeing knowing. How would you deal with the inescapable question, trapped inside a well, so to speak, when some intrepid person asks you, placing his hand on one of your eyes, “Do you see my cloak with your covered eye?”

 

Theaetetus: I will deny I see it with this eye, but with the other I say I can see it.

 

Socrates: So then, do you both see and not see the same thing?

 

Theaetetus: Indeed–– yet in this specified way.

 

Socrates: Yet I did not arrange the question in this way nor did I ask how, but whether that which you know is also that which you do not know. But now what you do not see you appear to see. And you happened to agree that seeing was knowing and not seeing was not knowing. Therefore from these things consider how it turns out for you.

 

Theaetetus: Yet I do consider that it is at odds with what I hypothesized (Translation mine, Theaetetus 165a2-d1). [2]

(Not all Platonic experiments on the eye are so compelling or provocative. Notably in the Timaeus, I think, it is given out as proof that light emanates from the eye on the grounds that if you squeeze it a light is seen!)

I really am attracted to this little scenario, especially in light of the current investigation as to whether perception is knowledge.  Perhaps I am taken in by the simple novelty of the experiment, attributing too much to it–– for example, Cornford seems to dismiss it as a “cavil” and sophistry unfair to Protagoras’ position.  Yet what is going on philosophically when the eye is covered?

Assuming that perceiving is knowledge, say we then proceed to cover one eye and look at an eye chart with our uncovered eye.  Socrates says this shows that we both know and don’t know, since we both see (with one eye) and don’t see (with the other eye).  This seems like an easy position to refute, even from a Platonic standpoint.  Elsewhere Socrates says that the eyes are merely instruments and that the soul is that which really sees; so in this case the soul, qua self, would know, yet could not be said to not know.

However, playing along, what does covering one eye and seeing with the other prove if perceiving is knowing?  That we neither know nor not know?  This seems absurd.  That we know?  Yet we also do not know, with the eye that is covered.  That we don’t know?  Yet we do know with the eye that is uncovered.  Perhaps then, it is a proof that we don’t know whether we know or don’t know, since we perceive that we both see/know with one eye and don’t see/know with the other, and to perceive is to know.  This then would be a self-defeating belief, it seems.

Furthermore, stepping away from the confines of this dialogue for a moment: is this a proof that seeing does not occur in the eye(s), but in the mind, and thus one explanation for how or why Plato created a distinction between the instruments of the self (body) and the self itself (soul)?

REFERENCES: 

[1] Starting at about 165a
[2] ΣΩ. Λέγω δὴ τὸ δεινότατον ἐρώτημα, ἔστι δὲ οἶμαι
τοιόνδε τι· “Ἆρα οἷόν τε τὸν αὐτὸν εἰδότα τι τοῦτο ὃ οἶδεν
μὴ εἰδέναι;”
ΘΕΟ. Τί δὴ οὖν ἀποκρινούμεθα, ὦ Θεαίτητε; (5)
ΘΕΑΙ. Ἀδύνατόν που, οἶμαι ἔγωγε.
ΣΩ. Οὔκ, εἰ τὸ ὁρᾶν γε ἐπίστασθαι θήσεις. τί γὰρ
χρήσῃ ἀφύκτῳ ἐρωτήματι, τὸ λεγόμενον ἐν φρέατι συσχό-
μενος, ὅταν ἐρωτᾷ ἀνέκπληκτος ἀνήρ, καταλαβὼν τῇ χειρὶ
(c) σοῦ τὸν ἕτερον ὀφθαλμόν, εἰ ὁρᾷς τὸ ἱμάτιον τῷ κατειλημ-
μένῳ;
ΘΕΑΙ. Οὐ φήσω οἶμαι τούτῳ γε, τῷ μέντοι ἑτέρῳ.
ΣΩ. Οὐκοῦν ὁρᾷς τε καὶ οὐχ ὁρᾷς ἅμα ταὐτόν;
ΘΕΑΙ. Οὕτω γέ πως. (5)
ΣΩ. Οὐδὲν ἐγώ, φήσει, τοῦτο οὔτε τάττω οὔτ’ ἠρόμην
τὸ ὅπως, ἀλλ’ εἰ ὃ ἐπίστασαι, τοῦτο καὶ οὐκ ἐπίστασαι.
νῦν δὲ ὃ οὐχ ὁρᾷς ὁρῶν φαίνῃ. ὡμολογηκὼς δὲ τυγχάνεις
τὸ ὁρᾶν ἐπίστασθαι καὶ τὸ μὴ ὁρᾶν μὴ ἐπίστασθαι. ἐξ
οὖν τούτων λογίζου τί σοι συμβαίνει. (10)
(d) ΘΕΑΙ. Ἀλλὰ λογίζομαι ὅτι τἀναντία οἷς ὑπεθέμην.