  Each context \(c\) is associated with a world, called ‘the world of \(c\)’. When a sentence is true with respect to context \(c\) and the world of \(c\), we say simply that the sentence is true at \(c\), without mentioning a world. But the notion of a sentence’s being true at context \(c\) and world \(w\) is more fundamental than the notion of a sentence’s being (simply) true at \(c\), for the latter notion is defined in terms of the previous notion. Now suppose that the two contexts mentioned above, \(c_1\) and \(c_2\), have the same associated world \(w_1\) (in which, recall, Mary is a philosopher but John is not). Then the sentence ‘I am a philosopher’ is true at context \(c_1\) and false at context \(c_2\).