Rudolf Carnap and W. V. Quine, two of the twentieth century's most important philosophers, corresponded at length--and over a long period of time--on matters personal, professional, and philosophical. Their friendship encompassed issues and disagreements that go to the heart of contemporary philosophic discussions. Carnap (1891-1970) was a founder and leader of the logical positivist school. The younger Quine (1908-) began as his staunch admirer but...