There are such criteria, and we will spend considerable time examining them in the following chapters. But first there are two fundamental concepts that must be understood in order for this criteria to be meaningful. Together, they form the basis of all truth and knowledge. Truth Corresponds to Reality Truth is a fact that, by its very nature, is immutable—it cannot change. As James Sire put it, truth is “propositional: a statement is true if what it says is so is so, or if what it says is not so