Contrarian is our own category, and we'll admit it: it isn't a school you'll find in a textbook. It's the thread of doubt that runs through all the others — the temperament of the questioner who pokes at received wisdom and refuses to take consensus on faith. Socrates played the gadfly of Athens; Diogenes mocked the powerful; Montaigne questioned everything, including himself; and later voices like Voltaire and Nietzsche made an art of it. Every era has had one — and every school was started by one.