In the course of the nineteenth century it became clear that the unfettered speculation obtaining in philosophy frequently could not be useful in science. However, in the Soviet Union it is asserted that natural science can draw its correct "theoretical conclusions" only by relying upon the philosophic and the methodological teachings of dialectical materialism. Certain Soviet Marxists have, on allegedly philosophic grounds, rejected Western genetics, the resonance theory of the chemical bond, the principle of uncertainty of quantum mechanics, relativist cosmology, the relativization of space, time, and matter, probability theory, and symbolic logic. The intriguing question then remains whether Soviet dialectical materialists determine the validity of scientific theories and accomplishments on the basis of a priori judgments derived from philosophic analysis or whether the Soviet attacks on Western scientific thought are, rather, political and ideological in nature.