History of Western Philosophy - Bertrand Russell [92]
That two shades of colour, both of which I am seeing, are similar or dissimilar as the case may be, is something which I, for my part, should accept, not indeed as a 'percept', but as a 'judgment of perception'. A percept, I should say, is not knowledge, but merely something that happens, and that belongs equally to the world of physics and to the world of psychology. We naturally think of perception, as Plato does, as a relation between a percipient and an object: we say 'I see a table.' But here 'I' and 'table' are logical constructions. The core of crude occurrence is merely certain patches of colour. These are associated with images of touch, they may cause words, and they may become a source of memories. The percept as filled out with images of touch becomes an 'object', which is supposed physical; the percept as filled out with words and memories becomes a 'perception', which is part of a 'subject' and is considered mental. The percept is just an occurrence, and neither true nor false; the percept as filled out with words is a judgment, and capable of truth or falsehood. This judgment I call a 'judgment of perception'. The proposition 'knowledge is perception' must be interpreted as meaning 'knowledge is judgments of perception'. It is only in this form that it is grammatically capable of being correct.
To return to likeness and unlikeness, it is quite possible, when I perceive two colours simultaneously, for their likeness or unlikeness to be part of the datum, and to be asserted in a judgment of perception. Plato's argument that we have no sense-organ for perceiving likeness and unlikeness ignores the cortex and assumes that all sense-organs must be at the surface of the body.
The argument for including likeness and unlikeness as possible perceptive data is as follows. Let us assume that we see two shades of colour A and B, and that we judge 'A is like B'. Let us assume further, as Plato does, that such a judgment is in general correct, and, in particular, is correct in the case we are considering. There is, then, a relation of likeness between A and B, and not merely a judgment on our part asserting likeness. If there were only our judgment, it would be an arbitrary judgment, incapable of truth or falsehood. Since it obviously is capable of truth or falsehood, the likeness can subsist between A and B, and cannot be merely something 'mental'. The judgment 'A is like B' is true (if it is true) in virtue of a 'fact', just as much as the judgment 'A is red' or 'A is round'. The mind is no more involved in the perception of likeness than in the perception of colour.
I come now to existence, on which Plato lays great stress. We have, he says, as regards sound and colour, a thought which includes both at once, namely that they exist. Existence belongs to everything, and is among the things that the mind apprehends by itself; without reaching existence, it is impossible to reach truth.
The argument against Plato here is quite different from that in the case of likeness and unlikeness. The argument here is that all that Plato says about existence is bad grammar, or rather bad syntax. This point is important, not only in connection with Plato, but also with other matters such as the ontological argument for the existence of the Deity.
Suppose you say to a child 'lions exist, but unicorns don't', you can prove your point so far as lions are concerned by taking him to the Zoo and saying 'look, that's a lion'. You will not, unless you are a philosopher, add 'And you can see that that exists.' If, being a philosopher, you do add this, you are uttering nonsense. To say 'lions exist' means 'there are lions', i.e. '"x is a lion" is true for a suitable x.' But we cannot say of the suitable x that it 'exists'; we can only apply this verb to a description, complete or incomplete. 'Lion' is an incomplete description, because it applies to many objects: 'The largest lion in the Zoo' is complete, because it applies to only one object.
Now suppose that I am looking at a bright red patch.