"Nothing" is an awe-inspiring yet essentially undigested concept, highly esteemed by writers of a mystical or existentialist tendency, but by most others regarded with anxiety, nausea, or panic. Nobody seems to know how to deal with it (he would, of course), and plain persons generally are reported to have little difficulty in saying, seeing, hearing, and doing nothing. Philosophers, however, have never felt easy on the matter. Ever since Parmenides laid it down that it is impossible to speak of what is not, broke his own rule in the act of stating it, and deduced himself into a world where all that ever happened was nothing, the impression has persisted that the narrow path between sense and nonsense on this subject is a difficult one to tread and that altogether the less said of it the better.

This escape, however, is not so easy as it looks. Plato...