THE ESSENCE OF TRUTH
'In regard to sound and colour: don't you first of all perceive, taking them in, that they both are?'
We perceive both colour and sound, both the blue of the sky and the song of the lark, first and foremost as existing, πρῶτον μὲν, 'in the first place', can be said only if something else is also perceivable, indeed something over which this 'in the first place' has priority. Thus Socrates says:
Οὐκοῦν καὶ ὅτι ἑκάτερον ἑκατέρου μὲν ἕτερον, ἑαυτῷ δὲ ταὐτόν;
[Theaetetus] Τί μήν;
'Not also (besides that they are perceived as beings) this, that each is different from the other and the same as itself?'
We perceive, therefore, the existing objects of perception: colour and sound. Colour is one being, sound is another; or to put it the other way around, the one exists as something different in relation to the other. As beings, both colour and sound are different to each other and the same as themselves. Different with respect to each other, the same with respect to themselves, the one and the other existing: just this is meant when we say that we perceive both as beings.
Καὶ ὅτι ἀμφοτέρω δύο, ἑκάτερον δὲ ἕν;
[Theaetetus] Καὶ τοῦτο.
Therefore both together, the one and the other, are two, and each on its own account is one?'
'Yes, that also.'
Only because the one being and the other being are perceived is it possible to count them. The one and the other are not already as such two; we must first add 'and' as a 'plus'. Every plus is an and, but not every and is a plus. A plurality is still not something countable as such, it is not yet a so-and-so-many. Both must first be given as beings, one and the other, and then we can take them as two, although we need not do so.
Οὐκοῦν καὶ εἴτε ἀνομοίω εἴτε ὁμοίω ἀλλήλοιν, δυνατὸς εἶ ἐπισκέψασθαι;
'Are you not also able to tell whether they are like or unlike each other?'