Action at the crossroads of its rationalities. prosaic aporias concerning cognitive individualism : raymond boudon and le sens des valeurs Cognitive individualism as developed by Raymond Boudon attempts to overcome the congenital limitations of rational choice models by restoring the Weberian concept ofaxiologic rationality, which would attest the scope and diversity of behaviors based on reason. Focussing exclusively on the case of traffic lights at crossroads - an example frequently used by Boudon to illustrate his theory - the article presents the various logical and methodological aporias of this typology of rationalities. In the case under consideration, instrumental rationality and axiological rationality prove to be indistinguishabl...