 C.I. Lewis (1912, 1914) defended the strict conditional analysis of subjunctives and developed an axiomatic system for studying their logic, but offered no semantics. A precise model-theoretic semantics for the strict conditional was first presented in Carnap (1956: Ch. 5). However, that account did not appeal to accessibility relations, and ranged only over logically possible worlds. Since counterfactuals are often non-logical, it it was only after Kripke (1963) introduced a semantics for modal logic featuring an accessibility relation, that the modern form of the strict analysis was precisely  formulated:[25]