Linguistic entailments occur when one may draw necessary conclusions from a particular use of a word, phrase or sentence. Entailment phrases are relations between propositions, and are always worded as, "if A then B," meaning that if A is true, then B must also be true. Another way of phrasing this is, "if A is true, then B must necessarily be true."
In semantics, entailments depend entirely on the denotation (also called the "dictionary definition" of the words in question). An example of this, as shown in M. Lynne Murphy's Lexical Meaning would be, "If it is a shoe, then it is made to be worn on a foot." This example references the 'footwear' meaning of the word shoe, and not the adjective, which is considered a different use of the word and thus a different meaning. For an entailment to be true, the then statement must always be true when the if statement is true. To judge whether an entailment is true, one can ask, "Could it ever be the case that B isn't true while A is true?" In order to accurately recognize entailments, a strong knowledge of the denotation of the word is required.
In pragmatics, entailment falls in a category with implicature and presupposition. All three deal with assumptions made by the listener or reader about a situation.
Entailment differs from implicature in that for the latter the truth of A suggests the truth of B, but does not require it. For example, the sentence "Jack missed the meeting after his car broke down" implies that Jack missed the meeting because his car broke down; but in reality Jack could have missed the meeting four days after his car broke down because he slept in too late. Entailments do not allow these reinterpretations.
Entailment also differs from presupposition in that in presupposition, the truth of what one is presupposing is taken for granted. The classic and often mentioned example of this is, "the king of France is not ill". This sentence presupposes that there is a king of France, which there is currently not. This means that though the sentence can be seen as logically true, it is normally interpreted as incorrect because there is no referent for "the king of France". Entailment also does not allow for a lack of referent.
- Beth, Evert Willem (1955). Semantic Entailment and Formal Derivability.
- Murphy, M. Lynne (2010). Lexical Meaning. Cambridge: Cambridge Textbooks in Semantics. pp. 31–40.
- Sauerland, U (2007). Presupposition and Implicature in Compositional Semantics. Pelgrave.