Scientists follow the scientific method, within which theories must be verifiable by physical experiment. The majority of prominent conceptions of God explicitly or effectively posit a being whose existence is not testable either by proof or disproof. Therefore, the question of God's existence may lie outside the purview of modern science by definition. The Catholic Church maintains that knowledge of the existence of God is the "natural light of human reason". Fideists maintain that belief in God's existence may not be amenable to demonstration or refutation, but rests on faith alone.