The paper starts with a presentation of three interrelated theses based on conceptual differentiations needed to account for the semantic complexity of the concept of rationality. The first thesis relates to the concept of observer's rationality. The logic of observation does not differ in respect to different types of object. Therefore rationality in the social sciences is in accordance with scientific rationality in general. The second thesis argues that the rationality of the observer is sufficient for economic and sociological inquiry, as demonstrated by the example of time series analysis. The third thesis refers to particular characteristics of human action that pertain to analysis in the social sciences. In many cases rationality of the observer in economics and sociology is tied to an assumption that the actor behaves with rationality (subjective rationality) in selecting the ends of action and the norms regulating social relationships. The three theses are then discussed in a context of reexamination of the works of historically important theorists, including the physiocrats, Bentham , Marx , Marshall , and Pareto , as well as more general methodological and philosophical traditions. (Eds.)