 If an argument is necessarily truth-preserving, the improbability of its conclusion cannot exceed the sum of the improbabilities of the premises. The latter was the criterion Adams used in constructing his logic. So Stalnaker’s logic for conditionals must agree with Adams’s over their common domain. And it does. The argument forms we showed to be invalid in Adams’s logic (§3.2) are invalid on Stalnaker’s semantics. For instance, the following is possible: in the nearest possible world in which you strike the match, it lights; in the nearest world in which you dip the match in water and strike it, it doesn’t light. So Strengthening fails. (By “nearest world in which …” I mean the possible world which is minimally different from the actual world in which … .) 