Since the two critiques [Iain McLean, Samual Postbrief, ‘"The Scientific Status of Political Science” — Two Comments,’ II (1972), 383–8] have little in common, I shall answer them separately beginning with McLean's. The main difficulty with McLean's argument is that he assumes that we know, or can know, that there cannot be a science of politics or, better still, laws of political behaviour as rigorous as the laws of the natural sciences. His assumption is supported by familiar arguments: men are not as passive and as homogeneous as silver nitrate; men have free will and could wilfully go against the predictions of the social scientist if only to show him that their behaviour cannot be predicted.