Traditionally, truth has been defined in philosophy as the agreement of the mind with reality. Pragmatists have no objection to this definition, but disagreement comes in when we try to define exactly what is meant by “agreement” and “reality.” The most common explanation of agreement is that it occurs when the mind copies reality. However, James criticizes this definition because it implies that truth is “inert and static” (77). Pragmaticism is interested in the impact something being true will make in our lives. He states a major principle: “True ideas are those that we can assimilate, validate, corroborate and verify”; and, conversely, “[f]alse ideas are those that we cannot” (77). For James, this means that truth is essentially a process: Things become true as we test and verify them by a process of being led from one idea to another. As we are led successively to new inferences and conclusions, we test them against the original idea, and if it harmonizes with the new ideas then we judge them to be true.

Elaborating on this pragmatic theory of truth, James starts with the premise that “the possession of true thoughts means everywhere the possession of invaluable instruments of action” (78).