The coherence theory of truth, or coherentism, asserts that truth is found in its coherence with a particular set of propositions. That is, we can know that an idea is “true” when it fits logically into a larger, more complex system of beliefs without contradicting anything. Looked at together, all the various parts of the belief system cohere, or unite, and this provides the basis for truth, at least within that set of beliefs. According to the coherence theory of truth, that which is false can be identified by the contradictions it raises within an existing framework of belief. Philosophers who have held to the coherence theory of truth include Leibniz, Spinoza, and Hegel.
To illustrate how the coherence theory of truth works, we can think of a child being told that 2 + 2 = 4. To determine if this is true, the child screens the idea through the belief system that he already has in place: he believes his teacher is honest, and he believes his experience is trustworthy—every time his teacher adds two blocks to the two already on the table, he counts four. So, he accepts the idea that 2 + 2 = 4; that notion coheres with what he already accepts as true.
Conversely, a man is told there is a ghost in the house, but he rejects the news because it conflicts with everything he already believes about life and death and spirituality. The idea of ghosts and hauntings does not cohere with the man’s existing set of beliefs. As a result, he considers the ghost theory to be false.
The coherence theory of truth diverges from its chief competing theory, the correspondence theory of truth, which says truth is that which corresponds to reality. That is, a truthful statement will describe things the way they really are. Truth will match reality, whether or not it coheres with a person’s framework of belief.
The coherence theory of truth is helpful in that it describes how we normally process new information, but it cannot truly tell us if something is true or false. In relation to the correspondence view, coherentism suffers from at least two shortcomings. To begin with, the statement truth is that which coheres is offered as a statement that corresponds to reality; therefore, the coherentist must depend on the correspondence theory of truth just to express what he believes.
A further weakness of the coherence view of truth is that a set of statements or propositions can be internally consistent even though they are false, i.e., the propositions present an argument for something that is not true. The child may believe that 2 and 1 are different ways of writing the same number, and his trusted teacher may use sleight-of-hand with the blocks to give him a validating experience. The child may then accept that 2 + 1 = 4, because it coheres with his set beliefs, as manipulated as they are. According to the correspondence theory of truth, however, 2 + 1 can never equal 4.
In the end, the correspondence theory of truth stands superior to the coherence theory of truth and any other proposed theories of truth. The correspondence theory of truth is based on objectivity, and the coherence theory of truth is based on subjectivity. Plus, all non-correspondence views are self-defeating. They imply a correspondence view of truth because the argument being made is said to correspond to what truly is, i.e., reality.