Jan Patočka, a disciple of Husserl and Heidegger, was the most eminent Czech philosopher of the 20th century. The article focuses on his concept of practical philosophy, which is seen as a constitutive force in European modernity. As such it has critical, dynamic, and stabilising effects. In this sense it is always closely related to politics and can both motivate social change and legitimise stable political orders. The consequences of this are demonstrated in liberalism and socialism as the two major projects of modern thought.