 At around the same time that Kaplan began developing his account of indexicals, logicians working on tense and modal logic had begun using 2D semantic frameworks to explain the behavior of sentential operators like ‘now’ and ‘actually’ (Åqvist 1973; Kamp 1971; Segerberg 1973; Vlach 1973). Unlike Kaplan, these logicians were not primarily concerned with the semantic rules governing natural languages. In particular, modal logicians were not focused on how the context in which an expression is used can affect its reference. Rather, they were interested in developing formal systems for representing valid inferences about time and possibility. It turns out that tense and modal logic are formally very similar and that both require double-indexing for expressive adequacy. Thus, to fully capture reasoning about what’s necessary and possible, we need to move from standard possible worlds semantics to a 2D semantic framework.