K. Truth
1. The nature of truth
a. Truth may be descriptive, applying to statements, propositions, or beliefs that are a) necessarily, i.e., analytically, true, as, e.g., "If p implies q and p is the case, then q is the case," or b) contingently, i.e., empirically, true, as, e.g., "The earth is round." "Truth" functions as an adjective, e.g., true beliefs.
b. Truth may be instrumental, applying to beliefs that guide thought or actions successfully, as, e.g., acting on the belief that fire burns helps one avoid getting burned. "Truth" functions as an adverb, e.g., One believes truly.
c. Truth may be substantive or ontological, referring to the real, as in "God is truth". Truth then functions as a noun.
d. Truth may be existential, referring to one's way of life or ultimate commitment. One lives rather than knows the truth. "Truth" then functions as a verb.
2. The criteria of truth
a. correspondence theory
That idea or proposition is true which accurately and adequately resembles or represents the reality it is supposed to describe; e.g., "It is raining now" is true if as a matter of fact rain is now falling.
This theory is usually that of epistemological realism (Aristotle, Locke, Russell).
An objection: it may be impossible to establish correspondence: "How can I know that my idea corresponds to its object even if in fact it does?"
Ideas are radically different from objects.
Austin modifies the theory to hold that the correspondence is in the nature of an appropriate correlation rather than congruity or resemblance. "The truth of a statement is a matter ... of the words used being the ones conventionally appointed for situations of the type to which that referred to belongs."
b. Coherence theory
That idea or proposition is true which "fits in" or is consistent with or is necessitated by the totality of truth of which it is a part. This theory is usually, though not necessarily, held by idealists (Hegel, Bradley, Blanshard). It is also held by nonidealists like Carnap and Neurath. An objections is that this theory assumes a metaphysical unity which may not exist. Also, as Russell points out, coherence may be a test or even a necessary condition of truth, but it is not what is meant by truth.
c. pragmatic theory
That idea or proposition is true which works or satisfies or is capable of doing so. Specifically:
1) James: "We cannot reject any hypothesis if consequences useful to life flow from it...If the hypothesis God works [for the individual]...it is true." Initially James defined truth as that which works. Later he defined it as
a) that which has "cash value"; i.e., is verifiable in principle
b) that which has coherence; i.e., fits present or anticipated facts
c) that which favors higher values; i.e. encourages progress
2) Pierce and Dewey: They give a social interpretation in terms of predictive power. Truth must be socially as well as experimentally verifiable -- not just privately useful. Truth is public, not private. "The opinion which is fated to be ultimately agreed to by all who investigate is what we mean by truth."