Let me begin by recounting a story I first heard almost fifty years ago. This is, of course, a long time and over the intervening years I have lost contact with the people involved. So it may well be that I have misremembered parts of it and the actual event may well have been somewhat different in its details. However, I will tell it as I recall it, and its general gist is enough to introduce my topic for this column.
Two graduate students, contemporaries of mine, married, saw the birth of a son and went together to study abroad. On one occasion, the wife went to the dentist, leaving the youngster in the care of his father, a somewhat absent-minded man. Sitting in the dentist's chair, the wife suddenly had an overpowering feeling that something awful had happened to the boy. So strong was this feeling that she got up at once and rushed home, to find that he had indeed fallen down a flight of stairs and suffered concussion, without the father's being aware of the event.