Overt intelligent performances are not clues to the workings of minds; they are those workings. Boswell described Johnson's mind when he described how he wrote, talked, ate, fidgeted and fumed. His description was, of course, incomplete, since there were notoriously some thoughts which Johnson kept carefully to himself and there must have been many dreams, daydreams and silent babblings which only Johnson could have recorded and only a James Joyce would wish him to have recorded.

Contemporary philosophers have exercised themselves with the problem of our knowledge of other minds. Enmeshed in the dogma of the ghost in the machine, they have found it impossible to discover any logically satisfactory evidence warranting one person in believing that there exist minds other than his own. I can witness what your body does, but I cannot witness what your mind does, and my pretensions to infer from what your body does to what your mind does all collapse, since the premises for such inferences are either inadequate or unknowable.

To see is one thing; to picture or visualise is another. A person can see things, only when his eyes are open, and when his surroundings are illuminated; but he can have pictures in his mind's eye, when his eyes are shut and when the world is dark.

... my today's self perpetually slips out of any hold of it that I may try to take.

So too Plato was, in my view, a very unreliable Platonist. He was too much of a philosopher to think that anything he had said was the last word.

Only through the medium of the public physical world can the mind of one person make a difference to the mind of another. The mind is in its own place and in each of us lies an inner life, the life of a ghostly Robinson Crusoe. People can see, hear, and jolt one another's bodies, but they are irremediably blind and deaf to the workings of one another's minds

Absolute solitude is on this showing the ineluctable destiny of the soul. Only our bodies can meet.