 Adams’s theory of validity emerged in the mid-1960s. “Nearest possible worlds” theories were not yet in evidence. Nor was Lewis’s result that conditional probabilities are not probabilities of the truth of a proposition. (Adams expressed scepticism about truth conditions for conditionals, but the question was still open.) Stalnaker’s (1968) semantics for conditionals was an attempt to provide truth conditions which were compatible with Ramsey’s and Adams’s thesis about conditional belief. (See also Stalnaker (1970), where the probabilistic aspects of his proposal are developed.) That is, he sought truth conditions for a proposition \(A\gt B\) (his notation) such that \(\mathbf{p}(A\gt B)\) must equal \(\mathbf{p}_A (B)\): 