This essay is written in the belief that it is possible to say both where Max Weber’s philosophy of social science is mistaken and how these mistakes can be put right. Runciman argues that Weber’s analysis breaks down at three decisive points: the difference between theoretical pre-suppositions and implicit value-judgements; the manner in which ‘idiographic’ explanations are to be subsumed under causal laws; and the relation of explanation to description in sociology. The arguments which Weber put forward are fundamental to the methodology of the social sciences, and since his death it has come to be increasingly widely held that with perhaps the sole exception of Mill’s System of Logic there is still no other body of work of comparable importance in the academic literature on these topics. Runciman’s attempt to correct Weber’s mistakes therefore constitutes in itself a valuable contribution to the philosophy of social science.