The major philosophical points I wish to make in this essay are not fully original, although I hope that what I have to say makes a coherent and persuasive whole. I shall be discussing a predominating philosophy of science that has held the field against most other systematic philosophies of science for at least five decades. Sometimes this philosophy has been called "Neo-Positivism," (in part to distinguish it from the nineteenth-century positivism of Comte) sometimes, "Logical Empiricism." It shares much with the early "Logical Positivism" of Schlick and other members of the Vienna Circle — a sophisticated philosophical position not to be confused with the positivism of Ayer's shallow Language, Truth and Logic — but for many advocates the historical roots lie elsewhere. The labels are not that important, especially since every essential ingredient of the philosophy of science I shall be discussing is to be found in much earlier, diverse philosophies. It is important, however, to pause and consider this historical situation. There are many twentieth-century philosophers who think that philosophy is an autonomous discipline whose history can be ignored; some contemporary philosophers regard philosophy of science as having come into existence only in this century, or maybe in the late nineteenth century.