Reflecting on the philosophical roots of the precautionary principle, this paper shows that two of its roots can be found in Hans Jonas’ Responsibility Principle: first, the idea of an (ethical) mastery of our (technical) mastery of nature, and second, the catastrophe threat and the adoption of the worst-case scenario. However, these ideas were first considered separately and then transformed. The idea of the mastery of our mastery was politically reinterpreted as a means of including citizens in technological choices. Jean-Pierre Dupuy has revisited the catastrophe idea in an attempt to give it a rationalist interpretation. Only by understanding the idea of nature as a complex notion can one overcome the limitations of each of these interpretations.