Grundy (2000: 121) divides presupposition into pragmatic presupposition and semantic presupposition. Pragmatic presupposition is cancelable where inconsistent with speaker or hearer knowledge about the world. Semantic presupposition is non-defeasible, contributes to the truth conditional meaning of the sentences. Brown and Yule (1983: 30) state that all of these presupposition are the speaker’s and all of them can be wrong or can be interpreted in other interpretation, since this sentences not speakers have entailment. Entailment means a term taken from logic, thus what is conveyed in an utterance will typically consist of what is said or entailed on the one hand and what is implied (Grundy, 2000: 81). Then, he asserts that entailments are conventional or semantic meanings that cannot by definition be cancelled without creating contradiction.
Renkema (1993: 154) says that presupposition is used to denote a special type of implicit information. In addition, presupposition is about the existing knowledge common to the speaker or the hearer that the speaker does not therefore need to assert. So, when the speaker or hearer, because of certain knowledge between them, understands certain information, the speaker does not need to assert that information explicitly (Grundy, 2000: 119).
