Plato
Phaedo
Penguin Classics. Translated by Christopher Rowe.

74b-84b
'Well, then,' said Socrates, 'see what you think of the following. We say, I suppose, that there's something that's equal – I don't mean a stick that's equal to a stick, or a stone that's equal to a stone, or anything like that, but some further thing over and above all of these, that is, the equal itself: are we to say that something of the sort exists,1 or not?'

'Zeus! Yes,' said Simmias; 'indeed we are, most emphatically!'

'And do we also know what it is?'

'Yes, definitely,' said Simmias.

'And where have we got our knowledge of it from? Isn't it from the things we were mentioning just now, that is, through seeing equal sticks or equal stones, or whatever else it may be - isn't it from these that we come to have that other equal in mind, even while it's distinct from them? Or perhaps you don't think it's distinct from them? Here's another consideration for you: even while being the same stones and sticks, aren't equal stones and equal sticks sometimes clearly equal to one stick or stone but not equal to another?'

'Yes, certainly.' -

'Well, did the equals by themselves2 ever appear clearly unequal to you, or equality inequality?'

'Not so far, Socrates.'

'In that case,' Socrates said, 'those other equals'3 and the equal itself are not the same thing.'

'It doesn't appear so at all, to me, Socrates.'

'And yet it's from these equals', said Socrates, 'even while they're distinct from that other one, that you've nevertheless come to have in mind, and gained, your knowledge of it?'

'Very true,' said Simmias.

'Then you've got that knowledge of it from them – whether it was like them or whether it was unlike them?'

'Yes, absolutely.'

'In any case it makes no difference. So long as, on seeing one thing, you come to have something else in mind, like or unlike, from seeing the first one,' Socrates said, 'what occurs must be recollection.'

'Yes, definitely.'

'Now do we have the following sort of experience in relation to what we perceive in the case of the sticks, and in general with all those pairs of equal things we were talking about just now: do they appear to us to be equal in the way that what's equal by itself is equal, or do they fall a bit short of that, in respect of being the kind of thing the equal is? Or are they entirely up to the mark?'

'They fall short by a long way,' replied Simmias.

'Well, do we agree that, when a person looks at something and thinks to himself, "This thing that I'm now seeing means to be the sort of thing that something else in the world actually is, but it's falling short, and is in fact incapable of being the kind of thing the other is; it's just not up to it" - someone who's thinking that must, I imagine, inevitably have had actual knowledge beforehand of the thing he's claiming that this other thing, the one in front of him, resembles but falls rather short of?'

'He must.'

'Well, then, is it or isn't it this sort of experience that we ourselves have in relation to those equal pairs and the equal itself? '

'It is, absolutely.'

'In that case we must have known the equal before the time when we first saw those equal pairs and thought to ourselves, "All these equals strive to be the sort of thing the equal is, but they fall rather short of it.'"

'That's so.'

'But we're also in agreement that we haven't got this thought, and couldn't have got it, from anywhere except from seeing, touching or one of the other kinds of perceiving; I'm counting all of them as the same in this case.'

'Yes, they are the same, Socrates, in relation to what the argument means to show.'

'But then it's precisely from our acts of perceiving that we must get the thought that all the equal things we perceive in those acts strive after what's equal by itself and fall rather short of it - or is this what we're saying?'

'Yes, it is.'
'In that case it must have been before we began seeing and hearing and using our other senses that we