Systems' rationality is an example of epistemology in Niklas Luhmann's work, for it produces a theoretical development that is critical of Jurgen Habermas' corresponding notion, prominent in its manifestation and promising in its proliferation. Luhmann owes much inspiration for his systems theory to the structural understanding of society and science. Thus, he attempts a deconstruction of the modern. In his understanding, since the Enlightenment, the modern presupposes but also produces reason, dialectics and the rationality of the sciences. The main argument of this chapter holds that instead of the formalism of systems theory, social enlightenment and political rationality are the outcomes of normative theory and rational praxis, which owe their validity and applicability to the formation of dialectical reason. Luhmann's reversal of critical theory into a traditional theory takes the form of a distortion of modernity in which systems theory is presented as the novel and innovative epistemology for modernity.