Presupposition
Authors: Sudo Yasutada 
Published: August 2014

Presupposition, broadly conceived, is a type of inference associated with utterances of natural-language sentences. Presuppositional inferences are distinguished from other kinds of inferences, especially from at-issue inferences (a.k.a. assertive contents), in that they generally convey backgrounded, uncontroversial information with respect to the context of utterance. For example, an utterance of “John forgot to call Mary” typically has a presuppositional inference that John was supposed to call Mary. It is intuitively clear that this is not the main point the speaker wants to make by the utterance. Rather, the at-issue content is that John didn’t call Mary (despite the fact that he was supposed to). Typically, the presuppositional inferences of an utterance are already known to be true and accepted by the conversational participants, or, at least, the speaker assumes so when the utterance is made. One caveat here is that presuppositional inferences may convey new information in some cases, although they are arguably exceptions rather than the rule. This exceptional behavior of presupposition is generally termed “accommodation” and has been treated as an important topic in the pragmatics of presupposition. Notice that in the pragmatic sense of the term, presuppositions include all sorts of assumptions that the speaker makes in uttering a sentence. In the above example, for example, it is also a presupposition of the utterance that the hearer or hearers understand English. Along with this pragmatic sense of the term, it is common in the literature to speak of presuppositions as part of the conventional semantic properties of sentences. To explicitly distinguish between these two uses of the term, the former is often called “pragmatic presupposition” and the latter is called “semantic presupposition.” Pragmatic and semantic presuppositions are closely related, in that an utterance of a sentence that has a semantic presupposition is associated with a pragmatic presupposition about the semantic presupposition, while a pragmatic presupposition does not necessarily stem from a semantic presupposition. For example, all sentences of the form “Subject forgot to VP” give rise to a pragmatic presupposition “Subject was supposed to or required to VP.” It is reasonable to assume that this pragmatic presupposition is due to the use of the word “forgot,” and the analysis of “forgot” as having a certain semantic presupposition as part of its meaning. On the other hand, the pragmatic presupposition that the hearers understand English is not attributable to the semantics of expressions used in this sentence. Recognizing semantic presuppositions leads to a number of theoretical questions: How does a semantic presupposition result in a pragmatic presupposition? What exactly are the semantic presuppositions and how should they be represented? Which expressions (words or constructions) have what kind of semantic presuppositions and why? How are semantic presuppositions of sentences computed in the compositional semantics? This last question, in other words, has to do with the way in which semantic presuppositions interact with other words and phrases, especially logical operators. For example, consider an utterance of the negation of the earlier sentence; that is, “John didn’t forget to call Mary.” It is noticeable that an utterance of this sentence has the same presuppositional inference as an utterance of its positive counterpart. More generally, presuppositional inferences are not negated by “not.” Such behavior of semantic presuppositions under various logical operators is called “projection”; projection of semantic presuppositions figures particularly prominently in the formal linguistic literature.