Willard Van Orman Quine was one the leading philosophers and logicians of the twentieth century, and perhaps the most prominent American philosopher of that century. A longtime professor at Harvard University, Quine is famous for defending a broad cluster of interrelated, "hard-headed" theses. There is no principled way to draw the distinction between analytic and synthetic propositions, he argued, and there is no principled way to fix on a single translation of a proposition in one language into another language. Quine had a long correspondence with Rudolf Carnap and shared in the scientism of the Vienna Circle, saying, for example, that the best method to fix on an ontology is to accept the existence of whatever entities are necessary in the refined language of science.