 Many types of conditional sentences, such as counterfactual conditionals, cannot be adequately expressed with truth-functional implication (material implication). Several formal interpretations of conditional sentences have been proposed. One of them, namely the Ramsey test, is particularly well suited to the formal framework of belief revision. It is based on a suggestion by F. P. Ramsey that has been further developed by Robert Stalnaker and others (Stalnaker 1968). The basic idea is that “if \(p\) then \(q\)” is taken to be believed if and only if \(q\) would be believed after revising the present belief state by \(p\). Let \(p\Rightarrow q\) denote “if \(p\) then \(q\)”, or more precisely: “if \(p\) were the case, then \(q\) would be the case”. In order to treat conditional statements on par with statements about actual facts, they will have to be included in the belief set, thus: