Abstract: typical of some contemporary theories of rationality is the pithily formulated idea stated almost 20 years ago by Gillian Rose (1947-1995) in her autobiography: «Reason, the critical criterion, is forever without ground». One important way of understanding this statement is found in the early writings of Karl R. Popper (1902-1994). This statement expresses the conviction at the root of Popper’s theory of rationality. This article begins with a brief presentation and analysis of Popper’s theory of rationality as it bears upon the question of violence. Afterwards, I turn to consider Ratzinger/Benedict XVI’s theory of rationality—as a response to Popper’s theory of rationality where critical reason is forever without ground. For Popp...