A general approach for determining the validity of commonsense assertions using conditional logics

An approach to theorem proving for the class of normal conditional logics is presented. These logics have been shown to be appropriate for representing a wide variety of commonsense assertions, including default and prototypical properties, counterfactuals, notions of obligation, and others. the logics are based on a possible worlds semantics but unlike the better‐known modal logics of necessity and possibility, they contain a binary “variable conditional” operator, ⟹, rather than a unary modal operator. the truth of a statement A ⟹ B depends both on the accessibility relation between worlds and on the proposition expressed by the antecedent A.