'Might', 'Would', 'Could' and a Compositional Account of Counterfactuals

International audienceThis paper has two purposes. We first give a new dynamic account of epistemic modal operators that account for both their test-like behaviour with respect to whole information states and their capacity to induce quantificational dependencies across worlds (modal subordination). We then use this theory, together with an analysis of conditionals and irrealis moods, to give a fully compositional semantics of indicative and counterfactual conditionals. In our analysis, the distinction between counterfactual and indicative conditionals follows directly from the interaction between the semantics of the conditional and irrealis operators and the semantics of the particular modals involved in the conditional consequent. We indicate some theoretical and logical consequences of our approach