This paper defines “institutions” in terms of saving-rationality devices. The first section draws a scheme of institutions’ evolution, from individual play to collective games until institutions properly so called. The second one deals with institutional rationality, by integrating into the classic explanatory/justificatory model of homo oeconomicus two other complementary models, homo sociologicus and homo psychologicus. The third section applies such conceptual tools to populism, defined in terms of adaptation of democracy to a mediatisated environment, in order to raise the problem of evolution/involution of institutions.
