In their search for truth, many of the great philosophers have looked to mathematics as a paradigm for how such a search should be undertaken. The reason is that mathematicians have a very precise notion of what truth is within their discipline. A proposition in mathematics is true if and only if it has been rigorously proved according to the very stringent laws of logic. Not everything can be proved, of course; we must start somewhere by making a few definitions and assumptions, but logicians and mathematicians keep these to a bare minimum. Moreover, they assume only those things that any reasonable person would agree to. Beyond that, deductive mathematics is essentially about seeking the truth, or falsity, of propositions by proof. In no other discipline is the standard of truth so high. No proposition, no matter how obvious, can be accepted as true until it has been...