The aim of this article is to show that Veblen and Commons’ Institutional Economics is an original translation of philosophical pragmatism in social science. The link between pragmatism and institutionalism is analyzed at two relied levels: the first concerns the conception of science and reality; the second concerns the conception of economic rationality and human behavior in society. We underline that the pragmatist vision about processes of thought linked to action and experience imply a renewal of the method as well as the subject of knowledge in economics, renewal which is characteristic of old institutionalism.