What can we Communicate?
The obvious answer to the question how we know about the experiences of others is that they are communicated to us, either through their natural manifestations in the form of gestures, tears, laughter, play of feature and so forth, or by the use of language. A very good way to find out what another person is thinking or feeling is to ask him. He may not answer, or if he does answer he may not answer truly, but very often he will. The fact that the information which people give about themselves can be deceptive does not entail that it is never to be trusted. We do not depend on it alone; it may be, indeed, that the inferences which we draw from people's non-verbal behaviour are more secure than those that we base upon what they say about themselves, that actions speak more honestly than words. But were it not that we can rely a great deal upon words, we should know very much less about each other than we do.
At this point, however, a difficulty arises. If I am to acquire information in this way about another person's experiences, I must understand what he says about them. And this would seem to imply that I attach the same meaning to his words as he does. But how, it may be asked, can I ever be sure that this is so? He tells me that he is in pain, but may it not be that what he understands by pain is something quite different from anything that I should call by that name? He tells me that something looks red to him, but how do I know that what he calls 'red' is not what I should call 'blue', or that it is not a colour unlike any that I have ever seen, or that it does not differ from anything that I should even take to be a colour? All these things would seem to be possible. Yet how are such questions ever to be decided?
In face of this difficulty, some philosophers have maintained that experiences as such are uncommunicable. They have held that in so far as one uses words to refer to the content of one's experiences, they can be intelligible only to oneself. No one else can understand them, because no one else can get into one's mind to verify the statements which they express. What can be communicated, on this view, is structures. I have no means of knowing that other people have sensations or feelings which are in any way like my own. I cannot tell even that they mean the same by the words which they use to refer to physical objects, since the perceptions which they take as establishing the existence of these objects may be utterly different from any that I have ever had myself. If I could get into my neighbour's head to see what it is that he refers to as a table, I might fail to recognize it altogether, just as I might fail to recognize anything that he is disposed to call a colour or a pain. On the other hand, however different the content of his experience may be from mine, I do know that its structure is the same. The proof that it is the same is that his use of words corresponds with mine, in so far as he applies them in a corresponding way. However different the table that he perceives may be from the table that I perceive, he agrees with me in saying of certain things that they are tables and of others that they are not. No matter what he actually sees when he refers to colour, his classification of things according to their colour is the same as mine. Even if his conception of pain is quite different from my own, his behaviour when he is in pain is such as I consider to be appropriate. Thus the possible differences of content can, and indeed must be disregarded. What we can establish is that experiences are similarly ordered. It is this similarity of structure that provides us with our common world: and it is only descriptions of this common world, that is, descriptions of structure, that we are able to communicate.
On this view, the language which different people seem to share consists, as it were, of flesh and bones. The bones represent its public aspect; they serve alike for all. But each of us puts flesh upon them in accordance with the character of his experience. Whether one person's way of clothing the skeleton is or is not the same as another's is an unanswerable question. The only thing that we can be satisfied about is the identity of the bones.
(From The Problem of Knowledge, By A. J. Ayer.)