The philosopher, John Wisdom once wrote, is like the obsessional neurotic who cannot leave his apartment without checking again and again to see whether he has turned off the lights or locked the door. These doubts of the neurotic seem peculiar in much the way that the "doubts" of the philosopher seem peculiar to the nonphilosopher. I speak here of skeptical doubts: Do we have knowledge of the "external" world? Can we have knowledge of other cultures? Can I even know my own mind?