He was a towering figure of the Enlightenment, influenced nearly all modern philosophers. In his writings, including his masterpiece, the Critique of Pure Reason (1781), he argued that we can only truly know that which can be proven by evidence. He placed the active, rational human being at the center of the cognitive and moral worlds. He suggested that we have a moral obligation, which he called the "categorical Imperative," to behave in an intrinsically good way under all circumstances -- not necessarily in ways that would make us happy, but in ways that would make us worthy of being happy. In his 1795 work Perpetual Peace, he quoted the Latin phrase "Fiat justitia, pereat mundus" ("Let justice be done, though the world perish"). He also criticized those who focused too much on religious ritual and church hierarchy as attempts to please the Creator without having to practice the actual principles of religion and righteousness.