 There is a contrast among pragmatic approaches to presupposition as regards whether the source of presuppositions is discussed. The approaches mentioned in the preceding paragraph, which attempt to derive presuppositional inferences from general conversational principles, aim to explain both the source of presuppositions, and the phenomenon of projection. But Stalnaker made no attempt whatsoever to explain where presuppositions came from, beyond indicating that they are inferential tendencies that might or might not be associated with semantic presuppositions. This emphasis on the projection of presuppositions rather than their source, which holds also of the contemporaneous work by Karttunen (1974; 1973), to which we shall turn shortly, lived on in much of the work influenced by these theories. It is particularly obvious in what we can collectively term cancellation-based theories of presupposition, led by Gazdar (1979a; 1979b), and including Soames (1979; 1982), Mercer (1987; 1992), Gunji (1981), Marcu (1994), Horton (1987), Horton and Hirst (1988), Bridge (1991), and van der Sandt (1982; 1988).