These words are comparable in denoting statements of fact or generality which are universally or widely considered to be true and fundamental. Principle has the greatest range of meaning of all the terms in this group, but in the context of this discrimination it refers to an elementary proposition held to be basic in any system or chain of reasoning, conduct or procedure: a theological principle ; the principle of self-government. In logic, an assumption specifically designates the minor or second premise in a syllogism. Less specifically, assumption refers to any assertion about reality which is unproved or debatable: the danger of basing scientific conclusions upon assumption . Axiom originally denoted a proposition, usually one agreed upon as the basis of an argument or demonstration, whose truth was so self-evident as to be indisputable: using the axiom that every effect must have a cause to prove the existence of God. In current usage, axiom often indicates any principle that men universally receive and act upon as if it were true, rather than something deemed necessarily true. A theorem is a proposition that is not self-evident but that is susceptible to rational proof. Since theorems are deduced from axioms , axioms are often called first principles , and theorems are called secondary principles .