Marx uses the term "praxis" to refer to the free, universal, creative and self-creative activity through which man creates and changes his historical world and himself. Praxis is an activity unique to man, which distinguishes him from all other beings. The concept appears in two of Marx's early works: the Economic and Philosophical Manuscripts of 1844 and the Theses on Feuerbach (1845). In the former work, Marx contrasts the free, conscious productive activity of human beings with the unconscious, compulsive production of animals. He also affirms the primacy of praxis over theory, claiming that theoretical contradictions can only be resolved through practical activity. In the latter work, revolutionary practice is a central theme: