A philosophical theory that it is impossible to arrive at a knowledge of reality, either because it is of its nature unknowable or because the human mind is unable to apprehend it. Its chief use is to deny that human reason can arrive at a knowledge of God and some truths of religion. This is opposed to Catholic Faith. The Vatican Council declares that "God, the beginning and end of all, can by the natural light of human reason, be known with certainty from the works of creation." The intention of the council was to reassert the historic claim of Christianity to be in accord with reason and to condemn the theory that all knowledge of God is derived from a primitive revelation.