Thought: A Journal of Philosophy
Making sense of our reasoning in disputes about necessary truths requires admitting nonvacuous counterpossibles. One class of these is the counteressentials, which ask us to make contrary to fact (and therefore contrary to possibility) suppositions about essences. A popular strategy in accounting for nonvacuous counterpossibles is to extend the standard possible worlds semantics for subjunctive conditionals by the addition of impossible worlds. A conditional A □ → C is then taken to be true if all of the nearest A worlds (whether possible or impossible) are C worlds. I argue that a straightforward extension of the standard possible worlds semantics to impossible worlds does not result in a viable account of counteressentials and propose an alternative covering law semantics for counteressentials.
Pearce, Kenneth L., "Counteressential Conditionals" (2016). Christ College Faculty Publications. 21.