This paper explores the sense in which modern societies can be said to be rational. Social rationality cannot be understood on the model of an idealized image of scientific method. Neither science nor society conforms to this image. Nevertheless, critique is routinely silenced by neo-liberal and technocratic arguments that appeal to social simulacra of science. This paper develops a critical strategy for addressing the resistance of rationality to rational critique. Romantic rejection of reason has proven less effective than strategies that (...) conceptualize modern artefacts, systems, and organizations as rationally underdetermined. This approach first appears in Marx's analysis of capitalist economics. Although he lacks the concept of underdetermination, Marx gets around the silencing effect of social rationality with something very much like it in his discussion of the length of the working day. Frankfurt School Critical Theory later blended romantic elements with Marxian ones in a suggestive but ambiguous mixture. The concept of underdetermination reappears in contemporary science and technology studies, now clearly articulated and philosophically and sociologically elaborated. But somewhere along the way the critical thrust was diluted. Critical theory of technology attempts to recover that thrust. Here its approach is generalized to cover the three main forms of social rationality. (shrink)