 As previously noted, early work on presupposition was primarily focused on definite descriptions, and definite descriptions have continued to be the paradigmatic example of a presupposition trigger in philosophical literature over the last fifty years. However, by the early 1970s, more linguistically oriented work had expanded the empirical domain of presupposition theory from definite descriptions to other trigger types, including factives (Kiparsky and Kiparsky, 1970), implicatives (Karttunen, 1971a), focus particles (Horn, 1969), verbs of judging (Fillmore, 1971) and sortal constraints (Thomason, 1972). Stalnaker’s discussion of Karttunen’s semifactives provides an early example of how this linguistic expansion of the empirical domain has impacted philosophical work. Also by the early 1970s, linguists had expanded the empirical domain in another direction. The philosophical literature was largely oriented towards unembedded presupposition triggers and triggers under negation, but as we have already mentioned, Morgan (1969) and Langendoen and Savin (1971) generalized the issue by considering arbitrary embeddings. However, it was not until Karttunen (1973) that the full complexity of the projection problem became apparent. By methodically considering projection behavior construction by construction, Karttunen showed that there was more variation in projection behavior than had been previously described, making it quite clear that none of the extant Frege-Strawson derived systems could hope to cover every case, and this ultimately led to the application of dynamic models of meaning to the problem of presupposition projection.