allegation [Lat. allegare ‘to send on an errand, to cite’] (also necessitation)

Term introduced by Sgall (Sgall et al. 1973:108-11) for a special type of implicational relations, which he defines as: from S follows A, but from not S, neither A nor not A follows. Along these lines, the concept of allegation lies between that of assertion, whose meaning is reversed through negation, and that of presupposition which remains constant under negation. The relation of allegation corresponds to the ‘if-verbs’ in Karttunen (1971). Applications for relations of this sort are found primarily in text linguistics.