“Counterfactual” readings of might/could have were previously analyzed using metaphysical modal bases. This paper presents examples and scenarios where the assumptions of such a branching-time semantics are not met, because there are facts at the base world that exclude the complement of the modal becoming true. Additional arguments show that counterfactual readings are context-dependent. These data motivate a semantics using a circumstantial (or factual) modal base, which refers to context-dependent facts about a world and time. The analysis is formulated in a version of the premise semantics for modality.