A discussion of the 'projection problem' of presuppositions. The idea that the presuppositions of a complex sentence can be defined as the logical sum of the presuppositions of its constituent sentences plus those of the main clause itself, is refuted. An instrument K. constructs for his argumentation is this threefold distinction in the set of predicates: 'plugs' (predicates blocking off all the presuppositions of the complement sentence; e.g. 'accuse' in 'Sheila accuses Harry of beating his wife'), 'holes' (predicates which let all the presuppositions of the complement sentence become presuppositions of the matrix sentence; e.g. 'surprise' in 'It surprised Mary that Fred had stopped beating his wife'); and 'filters' (predicates - in the logical sense - which , under certain conditions, cancel some of the presuppositions of the complement; e.g. 'if ... then' as in 'If baldness is hereditary, then all of Jack's children are bald' and 'If Jack has children, then all of Jack's children are bald').