Solving the Riddle of Coherence

A coherent story is a story that fits together well. This notion plays a central role in the coherence theory of justification and has been proposed as a criterion for scientific theory choice. Many attempts have been made to give a probabilistic account of this notion. A proper account of coherence must not start from some partial intuitions, but should pay attention to the role that this notion is supposed to play within a particular context. Coherence is a property of an information set that boosts our confidence that its content is true ceteris paribus when we receive information from independent and partially reliable sources. We construct a measure cr that relies on hypothetical sources with certain idealized characteristics. A maximally coherent information set, i.e. a set with equivalent propositions, affords a maximal confidence boost. cr is the ratio of the actual confidence boost over the confidence boost that we would have received, had the information been presented in the form of maximally coherent information, ceteris paribus. This measure is functionally dependent on the degree of reliability r of the sources. We use cr to construct a coherence quasi-ordering over information sets S and S’: S is no less coherent than S’ just in case cr(S) is not smaller than cr(S’) for any value of the reliability parameter. We show that, on our account, the coherence of the story about the world gives us a reason to believe that the story is true and that the coherence of a scientific theory, construed as a set of models, is a proper criterion for theory choice. When we are curious about what some corner of the world looks like, we can do all kinds of things to find an answer. We can go take a look ourselves, ask experts, consult textbooks, ... Sometimes the story that we get nicely falls into place like a jigsaw puzzle and we are confident that the story is true. Sometimes the story that we get just does not hang together and we are doubtful that the story is true. Philosophers have been very impressed by this item of common sense and have made it into the corner stone of their