What are commonly said to be communicated, apart from diseases, are ideas. An idea that has been occupying one mind gets duplicated, it would seem, in another mind. "Peering into the darkness of another's mind," in Santayana's phrase, we cannot easily say how faithful the duplication is. Such is the vagueness of the very idea of IDEAS, q.v., indeed, that it is anybody's guess what the form, content, and limits even of one of our own idea might be said to be. Anybody's guess including our own.
The nature and limits of communication can be somewhat clarified if we put the vaporous idea of ideas aside and address ourselves to tangible, visible, and audible reality. Simple sentences about this robust subject matter are apt to be unfailing vehicles of communication, especially if the objects concerned are of kinds that both we and our communicants continue to encounter from time to time. . . .
Examples taper off to where communication is less firmly assured, as when Hegel writes "Truth is in league with reality against consciousness," or I write "Logic chases truth up the tree of grammar." I am confident that I grasp and appreciate this message of Hegel's, and that there are philosopher's of logic who grasp mine. But mere acknowledgement, however sincere—"I dig you," or "I read you. Roger and over"—is not conclusive evidence of successful communication. The Latin pupil gets low marks who says "Oh, I know what it means, but I can't quite put it into words." Stage comics have dramatized failure of communication by protracted cross-purpose dialogue in which the audience is privy to the misunderstanding while the performers ostensibly are not.
There are objective checkpoints. We are content that we have communicated if our interlocutor reacts appropriately, perhaps by stepping briskly up onto the curb, or by looking up at a particular quarter of the night sky, or by continuing the dialogue in so penetrating way as to render cross purposes unthinkable. . . .
The farther we venture from simple discourse about familiar concrete things, however, the farther apart the checkpoints tend to be spaced and the less decisive each checkpoint tends to be. We discourse blithely to patiently receptive ears and pick up only an occasional inconclusive indication, if any, that we have communicated our idea (excuse the expression) or perhaps engendered some unintended one. No news is good news. We read the listener's mind by what Neil Wilson called the principle of charity. We get an exaggerated idea of how well we have been understood, simply for want of checkpoints to the contrary. The miracle of communication, in its outer reaches, is a little like the miracle of transubstantiation: what transubstantiation?
W.V.O. Quine on communication in Quiddities, 1987