 Stalnaker 1973 takes presupposition to be based on presumed common knowledge. Uttering a sentence like  (13) takes for granted that it is common knowledge that John is late. In this sense,  (13)  requires the context of utterance to be such that this common knowledge is in place. In contrast,  (14)  lacks such a requirement simply because the first conjunct in  (14)  asserts what the second conjunct takes for granted. The crucial assumption made by Stalnaker is that interpretation is incremental in the following sense: for a sentence of the form [\(S\)1 and \(S\)2], the interpretation of \(S\)2 occurs in a context which is already updated with \(S\)1. Schematically: