In Logic and Conversation, Grice (1975) considers the difference between what is uttered and what is meant. The main idea of this difference is that the addresser might mean more than what is actually uttered, i.e. by implying something different than what is said in a given context. Grice refers to these differences as implicatures and states that there are two ways in which the information can be implicated by the speaker: conventionally by conventional implicatures, closely related to what is said, and nonconventionally by conversational implicatures, closely related to certain features of the conversation.
Conventional implicit meaning refers to the information meant by the addresser without actually being part of what he/she utters, it is that information which is attached by convention to particular words or expressions, e.g. actually, moreover, therefore, but, yet, still. etc. In the example given by Grice (1975:44) "He is an Englishman; he is, therefore, brave." the word "therefore" implicates that his bravery is a consequence of his being an Englishman. According to Grice, the conventional implicatures do not affect the basic speech acts, but the less central ones, those that explain, compare, offer additional information, etc. Because of their connection to the words used by the addresser, they are closer to what is said than the conversational implicatures, still both types of implicatures offer additional information, an additional meaning to what is said, thus no implicature is directly connected to what is said. Conventional implicatures are very similar to presuppositions, Karttunen and Peters (1979) state that there is no clear distinction between them, Gazdar (1979) treats presuppositions as part of the conventional meaning of utterances and Yule (1996) connects the two notions by their association with specific words which result in additional meanings.
In the communication process the addresser treats some pieces of information as being already known by the addressee, it is the "given information" which is referred to as presupposition, some of the meanings being "encoded at this level" (Goddard, 2001:52). This information is usually not uttered, being treated as known, but it is taken as being part of the communication process even if it is not directly communicated. According to Goddard (ibid.) "Speech acts theorists would claim that presupposition is a necessary aspect of conversation, because it makes for economy, without which interactions would be hopelessly long-winded".
Besides what is assumed to be known and taken for granted, presuppositions are also characterised as having some assumed "common ground" between the participants (Stalnaker, 1978) or as an inference which is based "more closely on the actual linguistic structure of sentences" (Levinson, 1983:167). A distinction has been made between semantic and pragmatic presuppositions. Semantic presuppositions deal with the relationship between propositions or sentences while pragmatic presuppositions deal with propositions whose truth value have been taken for granted by the addresser, consisting of "previous information about the knowledge, beliefs, ideology and scale of values that the addressee must be acquainted with in order to understand the meaning of an utterance" (Alcaraz, 1999 cited in Bonyadi and Samuel, 2011:2). The assumed common knowledge is not always true, some propositions being accepted as true, but actually they are "not true, at all, or at least controversial" (van Dijk, 2000:10), therefore presuppositions may be used to influence the audience, to create different effects on the addressee. However, different alternative definitions have been proposed, there being no conflict between the semantic and pragmatic notions of presupposition.
The examples given by Yule (1996:26) who writes about presupposition as a relationship between two propositions, demonstrate that presuppositions have the property of remaining unchanged, true even if the statement is negated, this being actually one of the properties of presuppositions which is called constancy under negation:
"Mary's dog is cute." (=proposition p)
"Mary has a dog." (=proposition q)
"p presupposes (>>) q."
Even if we negate the first sentence, the relationship of presupposition remains the same:
"Mary's dog isn't cute." (=NOT p)
"Mary has a dog." (=q)
"NOT p >> q."
Properties of presuppositions
Constancy under negation
As it has already been illustrated with the examples cited from Yule (1996), presuppositions stand firm against negation, the negation actually sustaining the presuppositions, thus both the utterance and its opposite variant have the same presuppositions.
This property refers to the fact that presuppositions seem to be attached to some aspects of the surface structure of an utterance. In the case of proper names, for example, we can speak of presuppositions of existence, in the case of factitive or judgement verbs, there is the presupposition of truth related to the complement clauses which are attached to them.
The projection problem is related to the context as presuppositions sometimes survive or do not survive in different linguistic contexts. Presuppositions behave differently in simple sentences than in complex sentences as they may sometimes fail to be projected on a complex sentence.
This property refers to certain contexts in which presuppositions can be eliminated, cancelled. Levinson (1983:186) states that "one of the peculiar things about presuppositions is that they are liable to evaporate in certain context". This defeasibility is related to the common knowledge of the participants, the presuppositions arising when being consistent with this knowledge and disappearing when they are no longer consistent.
Types of presuppositions
As we have already stated in the detachability property of presuppositions, they are attached to different constructions, which are known under the name of presupposition triggers and which generate different types of presuppositions. The presuppositions triggers presented below are the most commonly used. Karttunen (1974), for example, has made a list of thirty-one presupposition triggers, but our aim is not to present all these types, but to categorize presuppositions according to the most common triggers. For this purpose, we are mainly going to use Yule's (1983) category of presuppositions.
In this type of presuppositions the addresser is bound to the existence of the things/beings presented. These presuppositions are present in the following constructions:
e.g. "Mary's brother bought three horses." (Yule, 1983:25) which presupposes, among other things, that Mary exists and that she has a brother.
Definite noun phrases
e.g. "the King of Sweden", "the cat", "the girl next door", "the Counting Crows" are all entities to the existence of which the speaker is assumed to be committed. (ibid.:27)
These presuppositions are linked to certain verbs, the information that follows these verbs being treated as true. Factive verbs treat their complements as fact: "know", "be aware", "regret", "realize", etc.
e.g. "She didn't realize she was ill." >> "She was ill."
"We regret telling him." >> "We told him."
"I wasn't aware that she was married." >> "She was married." (ibid.:28)
"The use of one form with its asserted meaning is conventionally interpreted with the presupposition that another (non-asserted) meaning is understood." The difference between factive and lexical presuppositions is that with factive presuppositions the information that follows a certain expression is considered to be true, while with lexical presuppositions the expression used is taken to presuppose something that has not been stated.
In the case of lexical presuppositions, we can refer to lexical items such as:
e.g. "John managed/didn't manage to open the door." >> "John tried to open the door." (Levinson, 1983:181). The idea that the person tried to open the door is the non-asserted meaning, the direct assertion being actually that the person succeeded in opening the door.
Change of state verbs
They describe a new state or a sort of change of state, presupposing that the new state din not exist before.
e.g. "He stopped smoking." >> "He used to smoke."
"They started complaining." >> "They weren't complaining before." (Yule, 1983:28).
e.g. "Jimmy is/isn't as unpredictably gauche as Billy." >> "Billy is unpredictably gauche." (Levinson, 1983:183).
Such adverbs as "again" or "too" presuppose the repetition of something.
This category refers to verbs which are usually constructed with the morpheme "re", for example "reuse", "reinvent", "reapply", etc.
In the case of structural presuppositions the given information is assumed to be true by the addresser who expects that the addressee also accepts it as being true. They are usually associated with Wh-questions or Yes/No questions, the information following these questions being presupposed as necessarily true by both addresser and addressee. These types of presuppositions that are based on the sentence structure represent subtle ways of making the addressee believe something that the addresser wants him to believe.
e.g. "How fast was the car going when it ran the red light?" - If the question is answered as asked, then the addressee would appear to be accepting the truth of the presupposition, i.e. the car ran the red light. (Yule, ibid.:29).