Rationalism is the view that “regards reason as the chief source and test of knowledge” or “any view appealing to reason as a source of knowledge or justification”. More formally, rationalism is defined as a methodology or a theory “in which the criterion of the truth is not sensory but intellectual and deductive”. Rationalists believe reality has an intrinsically logical structure. Because of this, rationalists argue that certain truths exist and that the intellect can directly grasp these truths. That is to say, rationalists assert that certain rational principles exist in logic, mathematics, ethics, and metaphysics that are so fundamentally true that denying them causes one to fall into contradiction.