The sciences are differentiated precisely on the basis of the particular contradictions inherent in their respective objects of study. Thus the contradiction peculiar to a certain field of phenomena constitutes the object of study for a specific branch of science. For example, positive and negative numbers in mathematics; action and reaction in mechanics; positive and negative electricity in physics; dissociation and combination in chemistry; forces of production and relations of production, classes and class struggle, in social science; offence and defense in military science; idealism and materialism, the metaphysical outlook and the dialectical outlook, in philosophy; and so on—all these are the objects of study of different branches of science precisely because each branch has its own particular contradiction and particular essence.