Schumpeter wrote that a “scientific” economist is competent in three “techniques”: economic theory, economic history, and statistics. In addition, he mentions economic sociology. The current interpretation is that theory, history, and statistics refer to aspects of research that can emerge in any field of science. Their content and relations can be clarified with Mach's writings. Economic sociology is not a technique within economics, but a part of general sociology. The rationale of economic and general sociology becomes clear by considering Schumpeter's interpretations of Marx's ideas. Schumpeter's ultimate ambition may have been a grand theory following Marx's vision.