An analysis of Pareto’s action theory making use of practical syllogism has as a result the differentiation of an externalist and an internalist part of his model of action. The externalist part is positivist in character and therefore unacceptable. It contains two classical positivist positions: a strict demarcation between metaphysics and science and the conspiracy-theory of error. Both were rightly criticised by Karl Popper. The internalist part contains the principle “reasons as causes”, which was later made famous by Donald Davidson. In comparison with Max Weber it will be shown that this is the rationality principle of interpretative sociology. Bringing internalist and externalist perspective together Pareto’s position can be called hermeneutical positivism. The article describes an hitherto neglected effect of positivist epistemology on sociology, and specifies action-theoretical fundaments of interpretative and explanative sociology.