 The product of modal systems, with its n-dimensional nature, is a very useful tool and, in particular, it has been of help for dealing with the philosophical semantics technique of  two-dimensionalism  (see also Chalmers 2006; Stalnaker 1978). This technique has been applied in different fields. In linguistics, it is the basis of David Kaplan’s semantic framework for  indexicals  (Kaplan 1989), which in turn has been used to explain conventional semantic rules governing context-dependent expressions as ‘I’ and ‘now’. Consider, for example, a setting built to talk about the features of a group of friends at different times; the context in which formulas will be evaluated can be defined as a tuple \((w, a, m)\), with \(w \in W\) a possible world, \(a \in \ttA\) an agent within that world and \(m \in T\) a moment in time when the agent exists in that world. Then, a sentence of the form “I am tired now” corresponds simply to an atom “tired”, with its truth-value being potentially different in different contexts, depending on whether, in the given world w, the given agent a is tired at the given moment m. Moreover: suppose the setting contains an alethic possibility relation between worlds \((R \subseteq W \times W)\), a friendship relation between agents \(({\asymp} \subseteq \ttA\times \ttA)\) and a temporal future relation between moments \((R_G \subseteq T \times T)\). Then, one can use matching modalities (the universal ones, \(\oBox\) and \([\asymp]\), for the first two; the existential one \({F}\) for the third) to express sentences as “I have a friend who is playing right now and necessarily will be tired at some moment later” \((\langle \asymp\rangle(\textit{playing} \land \oBox F\textit{ tired}))\) and “if one of my friends is playing now, all of them might be playing later” \((\langle\asymp\rangle \textit{playing} \rightarrow \Diamond F[\asymp]\textit{playing})\).