Action research and activity theory are considered by a number of followers as socio-critical approaches, whereas others do not relate them to social-criticism and use them merely as methods to improve practice. This article searches for general insights in Kurt Lewin's and Lev S. Vygotsky's work into how one proceeds and acts critically. In their methodological writings, different levels of critique can be determined: First, there is a critique of psychology's scientific state of the art compared to modern natural sciences. This critique includes the demand not to divide issues of method from methodological ones. Second, both thinkers relate knowing to the power to intervene; they both perceive a close connection between scientific progress and the improvement of social practice. However, their standpoints diverge here. Lewin favors a mutual inspiration between science and social practice in terms of "art" and "revolutionary progress" but does not theorize a more fundamental connection between these domains. By contrast, Vygotsky assumes interdependence between scientific progress and the liberation of the entire societal basis of human development. This assumption was encouraged by his historical experience of the Russian Revolution, yet needs to be rethought in light of subsequent historical developments.