ENTAILMENT AND PRESUPPOSITION
Entailment is a relation between sentence meanings, or propositions. (Sometimes, speaking loosely, we talk as though it were a relation between sentences.) Presupposition can also be seen as a relation between propositions, although many linguists (including George Yule) prefer to see presupposition as strictly pragmatic, and a relation between a speaker and a proposition. In any case it is important to see that these are two independent kinds of relations. A proposition which is presupposed in a particular utterance may or may not also be entailed.
II. Entailment (||-).
A. A sentence (meaning) A entails B (A ||- B) if whenever A is true, then B must also be true. Entailment is a very strong kind of implication. It is a semantic relation — thus, it holds no matter what the facts of the world happen to be (it holds in all possible worlds).
(1) a. Mary broke the window ||- The window broke
b. Sue and Fred went to the party ||- Sue went to the party
III. Presupposition (>>).
A. Presuppositions are implications that are often felt to be in the background — to be assumed by the speaker to be already known to the addressee.
B. A good diagnostic: presuppositions are shared by members of ‘the S family’ — that is, they remain constant under
1. Negation (denial)
3. Embedding under modals (e.g. might, it is possible that)
4. Embedding as the antecedent of a conditional (i.e. in an if-clause).
Example: A speaker of any of the sentences below would be presupposing that there is a king of France.
(2) a. The king of France is bald.
b. The king of France is not bald.
c. Is the king of France bald?
d. The king of France might be bald/Possibly the king of France is bald.
e. If the king of France is bald, he should wear a hat in the winter.
C. A presupposition of the S family may or may not be entailed by S itself (as it is in the example above — see (2a)), but in any case it will not be entailed by the negated, questioned, modalized, or conditionalized sentences.
D. Some examples — the presupposition triggers are underlined in each example. For the first three categories, the presupposition is also an entailment of the S sentence (though not the negated version of S). For the last two, the presupposition is not entailed by S — these are sometimes called conventional implicatures.(3) Mary saw/didn't see the horse with two heads >> There exists a horse with two heads1. Definite referring expressions (singular terms).
(4) Kepler died/didn't die in misery >> There is some individual named Kepler
(5) Joan began/didn't begin planting tomatoes >> Joan had not been planting tomatoes before2. Change of state verbs (start, stop, continue, etc.).
(6) What Bill lost was/wasn't his wallet >> Bill lost something3. Clefts, other focusing constructions.
(7) It was/wasn't his wallet that Bill lost >> Bill lost something
(8) Bill lost/didn't lose HIS WALLET >> Bill lost something
(9) Tu es/n’es pas très grande (Fr., ‘You (fam.) are/are not very tall’) >> The addressee is a close friend, a social4. Honorific terms.
(10) He is an Englishman; he is therefore brave >> Being brave is a consequence of being English5. Various modifiers.
(11) Even Bill could solve that problem >> Bill is the last person you’d expect to be able to solve the problem