In the linguistic branch of pragmatics
, a presupposition 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:
- Do you want to do it again?
- Presupposition: You have done it already, at least once.
- Jane no longer writes fiction.
- Presupposition: It is assumed that Jane once wrote fiction.
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.
Crucially, negation of an expression does not change its presuppositions: I want to do it again and I don't want to do it again both presuppose that the subject has done it already one or more times; My wife is pregnant and My wife is not pregnant both presuppose that the subject has a wife. In this respect, presupposition is distinguished from entailment and implication. For example, The president was assassinated entails that The president is dead, but if the expression is negated, the entailment is not necessarily true.
Negation of a sentence containing a presupposition
If presuppositions of a sentence are not consistent with the actual state of affairs, then one of two approaches can be taken. Given the sentences My wife is pregnant
and My wife is not pregnant
when one has no wife, then either:
- Both the sentence and its negation are false; or
- Strawson's approach: Both "my wife is pregnant" and "my wife is not pregnant" use a wrong presupposition (that there exists an object which can be described with the noun phrase my wife) and therefore can not be assigned truth values.
Russell tries to solve this dilemma with two interpretations of the negated sentence:
- "There exists exactly one person, who is my wife and who is not pregnant"
- "There does not exist exactly one person, who is my wife and who is pregnant."
For the first phrase, Russell would claim that it is false, whereas the second would be true according to him.
Projection of presuppositions
A presupposition of a part of an utterance is sometimes also a presupposition of the whole utterance, and sometimes not. We've seen that the phrase my wife
triggers the presupposition that I have a wife. The first sentence below carries that presupposition, even though the phrase occurs inside an embedded clause. In the second sentence, however, it does not. John might be mistaken about his belief that I have a wife, or he might be deliberately trying to misinform his audience, and this has an effect on the meaning of the second sentence, but, perhaps surprisingly, not on the first one.
- John thinks that my wife is beautiful.
- John said that my wife is beautiful.
Thus, this seems to be a property of the main verbs of the sentences, think and say, respectively. After work by Lauri Karttunen, verbs that allow presuppositions to "pass up" to the whole sentence ("project") are called holes, and verbs that block such passing up, or projection of presuppositions are called plugs. Some linguistic environments are intermediate between plugs and holes: They block some presuppositions and allow others to project. These are called filters. An example of such an environment are indicative conditionals ("If-then" clauses). A conditional sentence contains an antecedent and a consequent. The antecedent is the part preceded by the word "if," and the consequent is the part that is (or could be) preceded by "then." If the consequent contains a presupposition trigger, and the triggered presupposition is explicitly stated in the antecedent of the conditional, then the presupposition is blocked. Otherwise, it is allowed to project up to the entire conditional. Here is an example:
- If I have a wife, then my wife is blond.
Here, the presupposition triggered by the expression my wife
(that I have a wife) is blocked, because it is stated in the antecedent of the conditional: That sentence doesn't imply that I have a wife. In the following example, it is not stated in the antecedent, so it is allowed to project, i.e. the sentence does
imply that I have a wife.
- If it's already 4am, then my wife is probably angry.
Hence, conditional sentences act as filters
for presuppositions that are triggered by expressions in their consequent.
A significant amount of current work in semantics and pragmatics is devoted to a proper understanding of when and how presuppositions project.
Accommodation of presuppositions
A presupposition of a sentence must normally be part of the common ground
of the utterance context (the shared knowledge of the interlocutors
) in order for the sentence to be felicitous. Sometimes, however, sentences may carry presuppositions that are not part of the common ground and nevertheless be felicitous. For example, I can, upon being introduced to someone, out of the blue explain that my wife is a dentist,
this without my addressee having ever heard, or having any reason to believe that I have a wife. In order to be able to interpret my utterance, the addressee must assume that I have a wife. This process of an addressee assuming that a presupposition is true, even in the absence of explicit information that it is, is usually called presupposition accommodation
. We have just seen that presupposition triggers like my wife
) allow for such accommodation. In important unpublished work, the philosopher Saul Kripke
noted that some presupposition triggers do not seem to permit such accommodation. An example of that is the presupposition trigger too
. This word triggers the presupposition that, roughly, something parallel to what is stated has happened. For example, if pronounced with emphasis on John
, the following sentence triggers the presupposition that somebody other than John had dinner in New York last night.
- John had dinner in New York last night, too.
But that presupposition, as stated, is completely trivial, given what we know about New York. Several million people had dinner in New York last night, and that in itself doesn't satisfy the presupposition of the sentence. What is needed for the sentence to be felicitous is really that somebody relevant to the interlocutors
had dinner in New York last night, and that this has been mentioned in the previous discourse, or that this information can be recovered from it. Presupposition triggers that disallow accommodation are called anaphoric
Other uses of the term
Critical discourse analysis
identifies the ideological function of presuppositions, particularly in the concept of synthetic personalisation
In epistemology, presuppositions relate to a belief system, or Weltanschauung, and are required for it to make sense. A variety of Christian apologetics, called presuppositional apologetics, argues that the existence or non-existence of God is the basic presupposition of all human thought, and that all men arrive at a worldview which is ultimately determined by the theology they presuppose. Evidence and arguments are only marshalled after the fact in an attempt to justify the theological assumptions already made. According to this view, it is impossible to demonstrate the existence of God unless one presupposes that God exists; modern science is incapable of discovering the supernatural because it relies on methodological naturalism and thereby fashions a Procrustean bed which rejects any observation which would disprove the naturalistic assumption. The best the apologist can do is to argue that the resulting worldview is somehow inconsistent with itself (for example, via the Argument from morality or via the Transcendental argument for the existence of God).