The paper gives an analysis of the conception of rationality of two influential representatives of the 20th century theory of urbanism, and their philosophical grounds. It also outlines the problem of modern rationality, questions its character and points out, that for the time being the transition to a new way of thinking is problematic.

The paper offers a brief outline of the presuppositions and consequences of modern urbanism, as well as of its ontology. The stress is put on the historical transformations of modern rationality and on depicting its efforts in carrying out its project.