Ramsey test

The Ramsey test (also called the Ramsey test for conditionals) is a proposal for how to evaluate and accept conditional sentences of the form ifp(then)q. Informally, the guiding idea is that, to decide whether to accept a conditional if-p-then-q in a given belief state K, one must hypothetically add p to K and revise K in a minimal and rational way to accommodate p; then, one must accept if-p-then-q if, and only if, q would be accepted in the resulting belief state. In contemporary formulations, the "minimal" change of belief is made precise by a belief revision operation or by a rule for changing probabilities or possible-world rankings, depending on the framework.

The test originates in a brief footnote in Frank P. Ramsey's 1929 essay General Propositions and Causality, but has since been developed in several overlapping research traditions, namely, in the theory of § Belief revision, in § Probabilistic approaches to conditionals, in § Possible-worlds semantics, and in dynamic and non-monotonic logics. The Ramsey test has also been shown to generate various "triviality" results when combined with seemingly natural constraints on rational belief change, leading to an extensive literature on how it should be formulated and where its limits lie.