On the Evidential Import of Unification

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Myrvold, Wayne C.
preprint description
This paper discusses the evidential import of two senses in which a hypothesis may be said to unify evidence. One is the ability of the hypothesis to increase the mutual information of a set of evidence statements; the other is the ability of the hypothesis to explain commonalities in observed phenomena by positing a common origin for them. On Bayesian updating, it is only Mutual Information Unification that contributes to the incremental support of a hypothesis by the evidence unified. This poses a challenge for defenders of a view that explanation ought to be taken as a confirmatory virtue that makes a contribution in its own right to incremental support; in order for such a view to be defensible, its advocates must ground it in some relevant difference between humans and a Bayesian agent. Options for such a defense are considered, and it is concluded that common origin unification has at best a limited heuristic role to play in confirmation. Finally, it is shown how Reichenbachian common cause hypotheses fit into the schema of mutual information unification.