Pragmatics
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. It is an implicit
assumption about the world or background belief relating to an utterance whose
truth is taken for granted in discourse. Examples of presuppositions include:
Amanda doesn’t sing anymore.
Presupposition: Amanda used to sing.
A presupposition must be mutually known or assumed by the speaker and addressee
for the utterance to be considered appropriate in context. It will generally remain a
necessary assumption whether the utterance is placed in the form of an assertion,
denial, or question, and can be associated with a specific lexical item or grammatical
feature (presupposition trigger) in the utterance. Negation of an expression does not
change its presuppositions:
I want to do it again
I don't want to do it again
Both presuppose that the subject has done it already one or more times;
An implicature, on the other hand, is something the speaker suggests or implies with
an utterance, even though it is not literally expressed. Conversational implicatures
are pragmatic inferences: unlike entailments and presuppositions, they are not tied
to the particular words and phrases in an utterance but arise instead from contextual
factors and the understanding that conventions are observed in conversation.
Implicatures can aid in communicating more efficiently than by explicitly saying
everything we want to communicate.
A (to a girl): I need some water.
B: I am not your housekeeper.
1
Here, B does not say (no), but conversationally implicates, that she won’t get him
water, because otherwise her utterance would not be relevant in the context.
One sentence may present both presupposition and implicature at the same time as
in the example:
John ate some of Judith’s cookies.
The implicature here is that John didn’t eat all of Judith’s cookies and the
presupposition is that Judith has cookies.