Critical theory's epistemological arguments were marshalled in a vehement critique of positivism, which marked its claims as a reaction against rational normativity, or as the new empiricist epistemology safeguarding scientific orthodoxy. This chapter explores the relevant exchange of arguments between critical theorists and positivists. It discusses the analysis of the three major thinkers of the Frankfurt School, Max Horkheimer, Theodor W. Adorno and Herbert Marcuse. The critical theory of the Frankfurt School challenged instrumentality whereby human beings become mere instruments along the lines set out by modern science. In order to deal with what constitutes science, epistemologically speaking, critical theory tackles the problem of scientific laws. The answer remains straightforward: whereas natural sciences facilitate the formation of scientific laws, it is rather unfeasible to expect the same degree of certainty in the humanities and social sciences. This chapter also presents an overview of the key concepts discussed in this book.