Karl Popper and Amartya Sen have developed social theories, which are very close to each other, though neither has taken notice of the other. The independent programs they propose for the development of their theories go astray, because they build on standard economic methods, albeit in different ways. A better approach for the development of each program can be found by using Popper's important, but in the methodology of the social sciences hitherto ignored discovery, that rationality is social. Important contributions of Sen to economic theory may then be developed in ways which also contribute to Popper's social theory.