 Ernest Adams, in two articles (1965, 1966) and a subsequent book (1975), gave a theory of the validity of arguments involving conditionals as construed by Supp. He taught us something important about classically valid arguments as well: that they are, in a special sense to be made precise, probability-preserving. This property can be generalized to apply to arguments with conditionals. The valid ones are those which, in the special sense, preserve probability or conditional probability. 