Natural science is differentiated from other modes of knowledge by method, not by subject matter. The revolutionary concept that social phenomena are natural phenomena and therefore can be studied by natural-science methodology is being rapidly accepted. Some of the most frequently used arguments that sociology "cannot be scientific" are refuted by showing the relative orderliness and approximate predictability of certain classes of social phenomena. Such prediction will never cover all aspects of social behavior. The same is true of the prediction of physical and biological phenomena.