  Sentences that are valid in standard (modal) first-order predicate logic are also valid in Kaplan’s logic of indexicals. But there are also valid sentences peculiar to Kaplan’s logic of indexicals. For instance, the formal analogs of ‘I exist’ and ‘I am here now’ are true in every context in every structure, and so are valid. This result is due to Kaplan’s stipulations that the agent of a context \(c\) exists at the time and world of \(c\), and that the agent of \(c\) is located at the position of \(c\) at the time and world of \(c\). In addition, every (formal) sentence of the form “\(S\) if and only if actually \(S\)” is valid. This is so because \(S\) is true at a context (in a structure) if and only if “Actually \(S\)” is.