  A striking feature of Kaplan’s logic is that some valid sentences are contingently true, at some contexts in some LD structures. One example is ‘I exist’. We saw above that it is valid. Now consider an LD structure \(M\) in which Mary exists at some of the worlds in \(M\) but fails to exist at others. (More exactly, Mary is in the extension of ‘Exist’ at some pairs \(\langle t, w \rangle\) but is not in the extension of ‘Exist’ at some other pairs  \(\langle t, w' \rangle\).) Next, consider a context \(c\) in which Mary is the agent. The formal analog of the sentence ‘I exist’ is true with respect to \(c\) and the time and world of \(c\) in \(M\), and so is true at \(c\) in \(M\). But that sentence is false with respect to \(c\), \(t\), and other worlds in \(M\). Therefore, ‘Necessarily, I exist’ (or its formal analog) is false at \(c\) in \(M\). Thus, ‘I exist’ is only contingently true at some contexts in some LD structures. Parallel points holds for ‘I am here now’: it is valid, but only contingently true at some contexts in some structures. Similarly, every sentence of the form “\(S\) if and only if actually \(S\)” is valid, but some sentences of this form are only contingently true at some contexts in some structures.