Presupposition Accommodation in Update Semantics

84 Pages·2007·0.73 MB·English

Presupposition Accommodation in Update
Semantics
Joris Hulstijn
(cid:3)
[email protected]
august 1995
Abstract
The study of presuppositions lies on the border of semantics and pragmatics. It concerns
information, assumed to be part of the discourse context by the speaker, as apparent in the
syntactic form of the utterance. Missing presupposed information will normally be (cid:12)lled in
bythehearer,provideditiscompatiblewiththecontext. Mythesistriestocharacterisethis
process of presupposition accommodation.
part I
In the (cid:12)rst part of this thesis I introduce some of the basic approaches to presuppositions.
First, I formulate some general characteristics. Then I present the ideas behind semantic
theories of presupposition: presupposition as a precondition on successful interpretation. I
introducetheprojectionproblemofpresuppositionsandtheproposedsolutionbyKarttunen.
Idiscussthein(cid:13)uenceofcontextandtherelatedpragmatictheoryofpresupposition: presup-
positionsaretakentobepartofthediscoursecontext,already. Iargueforanexplicitnotion
of presuppositionaccommodation: adjustment of the contextwhenpresupposed information
is missing. I discuss Gazdar's approach and compare it with Heim and Van der Sandt. My
approachis similarto Heim's.
part II
UpdateSemanticshasprovidedaframeworkinwhichthesebasicapproachescanbecompared.
Thecontext,roughlytheinformationstateofthehearer,canbemodelledasasetofepistemic
alternatives: ways the world can be according to the information. Increasing information by
updates, means eliminating alternatives. Presupposition accommodation can be modelled
using updates on stacks of information states. The di(cid:11)erent approaches from part I are
reformulatedasaccommodation strategies. Usingonlyafewbasictypesofstack-updates,the
strategies can becharacterised andcompared inthelogicalframework.
part III
Theoretical linguistics cannot do experiments to test its hypotheses. What we can do is
formalise our theories. The next step is to try and implement the theory in a computer
program. Ihavedone thisfor severalof theupdatesystems de(cid:12)nedinpartII.
I found a grammar that translates simple example sentences into the logical language. I
have chosen to use semantic tableaux to represent information states in the program. The
semantic tableaudeductionmethod can be seen as a Constructive Update System. Branches
playtheroleofepistemicalternatives. Forpropositionallogicthiscanbeimplementeddirectly
intoProlog. Thegreatestproblemhasbeenwiththeinterplaybetweennegationanddiscourse
referents in the predicate logic version of the program. Stacks of information states can be
simulated using a preprocessing approach. The formula is (cid:12)rst brought into normal form,
resolvingoraccommodatingpresuppositionsusingasimulatedstackstructure. Thenupdates
canbe dealtwithbya simpletheorem provercalledLeanTap.
0Thisthesisistheresultofmyresearchprojectat(cid:11)-Informatica,Faculty ofArts,University ofAmsterdam.
I like to thank my supervisor, Henk Zeevat forhis trust in the project. I also like to thank Frank van Harmelen,
Jelle GerbrandyandJanJaspersfortheiradviceandforcorrecting earlydrafts. Allmistakesaremine.
0
Contents
I In Which Several Accounts of Presupposition Are Introduced and
Discussed 3
1 Characteristics 3
2 Semantic Presupposition 5
3 Presupposition Projection 6
4 Pragmatic Presupposition 8
5 Gazdar 13
6 Heim 15
7 Van der Sandt 19
8 Conclusions 24
II A Presupposition Operator in Update Semantics 26
9 Update systems 26
9.1 Update SemanticsUS : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 28
9.2 Dynamic Logicsfor PredicateLogic : : : : : : : : : : : : : : : : : : : : : : : : : : 30
9.3 Attitudes and Modals : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 32
10 Presupposition in Updates 34
10.1 Local Strategies : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 36
10.2 InformationStacks : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 39
10.3 Strategies with Stacks : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 40
11 Conclusions 43
III Implementing Alternatives 45
12 Grammar 46
13 Representation 48
13.1 Semantic Tableaux : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 48
13.2 Constructive Update Semantics(CUS): : : : : : : : : : : : : : : : : : : : : : : : : 49
13.3 Constructive Update Semanticsfor PredicateLogic(CUSPL) : : : : : : : : : : : 53
13.4 implementing(M)DL : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 55
1
13.5 LeanTap : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 58
14 Presupposition Implementation 61
14.1 Direct Implementation : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 61
14.2 Abstract Implementation : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 65
14.3 PreprocessingImplementation : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 67
15 Conclusions 69
IV Appendices 71
A CUSPL 71
0
B implementing US 72
C LeanUpd 76
D Preprocessing 77
2
Part I
In Which Several Accounts of
Presupposition Are Introduced and
Discussed
1 Characteristics
In this section will outline the main characteristics of presupposition using examples from the
linguistic literature. I will discuss several accounts of presuppositional inference that have been
proposed to deal with these examples.
The following sentences contain examples of linguistic constructions that give rise to presup-
positions. The presupposition inducing constructions, or triggers, in the (a) and (b) sentences
1
presuppose the (c) part. That is, we can infer that the (c) part must be true.
(1) de(cid:12)nite descriptions
a. The chief of Buru-Buru is bald.
b. The chief of Buru-Buru is not bald.
c. There exists a chief of Buru-Buru.
(2) factives
a. John regrets that he killedhis wife.
b. John does not regret that he killedhis wife.
c. John killedhis wife.
(3) lexicals
a. Jack is a widower.
b. Maybe Jack is not a widower.
c. Jack is an adult male.
(4) proper names
a. Bill willhelp you out.
b. ProbablyBill willhelp you out.
c. There is somebody calledBill.
(5) quanti(cid:12)ers
a. Most of Jack's childrenare happy.
b. If Jack buys ice-cream,most of Jack's childrenare happy.
c. Jack has children.
(6) clefts
a. It was Julius who solved the problem.
b. Jack believesthat it was Juliuswho solvedthe problem.
b. There is somebody who solved the problem.
Itseemsimpossibletobringsuchdiverselinguisticconstructionsunderoneheading. Yetallthese
constructions share some important characteristics. The characteristics set apart presupposition
1Amoregeneral notion of presupposition: what needs to be presumed in orderto understand an utterance, is
dealtwithinsection 4.
3
from other types of inference. They are also what makes presupposition such an interesting
2
phenomenon. How can we explainthe followingthree types of characteristicbehaviour?
(i) Presupposition triggers can be embedded under a negation or under other constructions, es-
peciallymaybe, without losingthe inference that the presuppositionmust be true. Example(1a)
presupposes there is a chief of Buru-Buru. The embedded (1b) still presupposes there is a chief
of Buru-Buru. Using a factive verb like regret in (2a) presupposes its complement. The negation,
(2b), only asserts something about John's lack of hard feelings towards the killing. It still pre-
supposes he did kill her. In general an expression has an assertive and a presuppositional part.
3
Embedding constructions like negation or maybe only a(cid:11)ect the assertive part. For instance
(3b) asserts that it is conceivable Jack did not lose his wife. The presupposition that Jack is
an adult male remains. There are all kinds of embedding constructions that do not a(cid:11)ect the
presuppositionalinference. In (4b) the modalityprobably , in(5b) the hypotheticalcircumstances
described in the if-clauseand in (6b) the propositionalattitude belief do no limitthe presupposi-
tionalinference. Thischaracteristicmarksthemaindi(cid:11)erencebetweenpresuppositionalinference
and normalentailment.
(7) a. Nine of the ten marblesare in the bag.
b. It is not the case that nine of the ten marblesare in the bag.
c. Maybe nine of the ten marblesare in the bag.
d. John believesthat nine of the ten marblesare in the bag.
Thepresuppositionoftheexpressionthetenmarblesthattherearetenmarblesof(7a)ispreserved
in (7b), (7c) and (7d) . The content of the sentence entails by some simple arithmetic, that one
marbleismissingfromthebag. Thisentailmentisnotpreservedin(7b). Thatitisnotpreserved,
can be tested by a follow-up sentence that needs the entailment. For instance we can't say `it is
under the couch.' referring to the missing marble. In (7c) and (7d) the entailment is limited to
the contexts introduced by maybe or by John's beliefs.
(ii) On the other hand, in particular circumstances presupposed information is not preserved.
Examples(8)and(9)containthesametriggersasexamples(5a)and(2a)above. Yettheinferences
to(5c)and(2c)cannotbemade. Insomeframeworkssuchnon-preservedpresuppositionsaresaid
to be blocked or cancelled.
(8) If Jack has children,most of his children are happy.
(9) John does not regret that he killedhis wife, because he did not do it.
(iii) In case a presupposition is known not to be ful(cid:12)lled, the result of the interpretation of the
sentence that triggered it, becomes undetermined. Compare the followingexample with example
(1).
(10) a. The present King of France is bald.
b. The present King of France is not bald.
EverybodyknowsthatthereisnoKingofFranceatthistimeandplace. Howcanwesayofanon
existing referent that it be bald? Or indeed, how can we say that it is not bald? Suppose that
sentences are interpreted to be either true or false. Now suppose, like Russell, (e.g. [37]) that we
take it to be part of the meaning of a de(cid:12)nite descriptionlikethe king of France that there exists
4
a unique such thing, then (10a) must be false. Now since (10b) is the logical complement of
2I realise that these characteristics are not theory independent. I hope to show in the following sections from
whattheorytheyoriginate.
3Theassertivepartisalsocalled thesemanticortruth conditionalcontent.
4IntherestofthethesisIwillnotdiscusstheuniquenesspresupposition.
4
(10a), we expect (10b) to be true. But that is just as wrong! So it seems that we cannot give a
5
de(cid:12)nite truth value. The result of interpretationremainsundetermined.
These combined characteristics make presuppositional inference hard to explain. Theories that
explain one or two characteristics often miss out on a third. In this part I will present some
accounts of these and other characteristics of presuppositions. In the end I will have collected a
number of principleseach presuppositiontheory should satisfy.
2 Semantic Presupposition
Take a sentence with a non-referring expression like (10). How did the notion of presupposition
get into the picture? Assume an intensional semantics. Expressions both have a referent and a
sense. The referent of a sentence is it's truth value. The sense of a sentence can be seen as the
circumstances under which the sentence would be true. Both de(cid:12)nite descriptions and proper
names have the object or person they refer to as their referent, provided such object exists. The
sense of a de(cid:12)nite descriptionisgivenby the descriptivecontent of the noun. Propernameshave
6
nosensethatisdirectlyavailablefromitsform. Thereferentofacomplexsentenceisdetermined
compositionally from the referents of its parts.
We know what it would mean for some King of France to be bald, if there were one. Sentence
(10a) does have a sense. The de(cid:12)nite description the present king of France has no referent.
Becauseofthe compositionalityof referencethe completesentencewillalsolackareferent: it has
no de(cid:12)nite truth value. Can we predict under what condition a sentence will lack a truth value?
Yes,accordingtothepreviousreasoning,whenasub-expressionlacksareferent. Suchacondition
for sentences lacking a de(cid:12)nite truth value is called a presupposition. So a de(cid:12)nite description
presupposes the existence of a referent.
If we extend the account from referring expressions to other constructions that would make the
sentence truth valueless, we get the following semantic de(cid:12)nition of presupposition. (Strawson
7
[45] )
de(cid:12)nition 1 (semantic presupposition)
(cid:30) presupposes (cid:31) just in case (cid:30) is true nor false unless (cid:31) is true.
Suppose we wouldwant to makethe semanticnotion of presuppositionprecisein a logicalframe-
work. Obviously we would need a non-bivalent base-logic. So assume we have a logic with truth
values f1;0;#g. (true, false, unde(cid:12)ned) A trigger with assertive part (cid:30) and potential presup-
position (cid:31) is written in the logical language as (cid:30)(cid:31). We now need to (cid:12)nd a truth table for the
8
construction (cid:30)(cid:31). Soames[42] and Van der Sandt [38] showed that such a truth table can never
befound. Hereanexplanationofcharacteristics(i)and(iii)clasheswith(ii). Reconsiderexamples
(5b) and (8). Their logicalform can be brought out as:
(5b) !:(cid:30)(cid:31) presupposes (cid:31)
(8) :(cid:31)!:(cid:30)(cid:31) does not presuppose (cid:31)
In both cases we come across the construction (cid:30)(cid:31). In (5b) the presuppositional inference is
preserved: the sentence lacks a truth value when the presupposition is not ful(cid:12)lled. So for all
valuations v, (rows in the truth table) if v((cid:31)) = 0 or #, then v((cid:30)(cid:31)) must be #. In (8) the
presuppositionalinferenceislost. If thepresuppositionisnotful(cid:12)lled,thesentencemaystillhave
atruth value. Soif v((cid:31))=0or#, then v((cid:30)(cid:31))=1or0. Notruth tablede(cid:12)nitioncansatisfyboth
requirements. The only way to save this, would be to make the construction (cid:30)(cid:31) or the de(cid:12)nition
of negation ambiguous. However, that would be very unsatisfactory. It would not really explain
5The alternative is that (10b) is false. In Russell's view all presuppositions that are known to be untrue, lead
tofalsity. Thatwouldmeanthat(10b)isnolongerthelogical complement of(10a).
6Orpossiblynosenseatall. Thisisquestion ismuchdebated.
7Disregardingthedi(cid:11)erencebetween FregiansentencesandStrawsonian statements
8Fortheotherconnectives, takeeitherKleene'sstronglogic orsomeothernon-bivalent logic.
5
the phenomenon. The ambiguity only comes up in connection with presuppositions. There are
no independent reasons for assuming ambiguity of negation or the (cid:30)(cid:31) construction. So a purely
semanticaccount fails. (see also section 4)
However a weaker version of the semantic de(cid:12)nition remains possible. In the rest of the paper I
willassumethefollowingprinciple. Itholdsforlexicalpresuppositionsandforthefactives. Italso
seemstoo hold for existentialpresuppositions,likethe de(cid:12)nites and possessives. It is unclearif it
wouldholdforaclassofpresuppositionsthatIdonotdiscussinthisthesis,namelypresuppositions
induced by connectives liketoo, even or but.
principle 1 (presupposition as precondition)
A presupposition is a precondition on successful interpretation.
This is meant as a principle to guide intuitions. I believe that the analogy with the technical
term precondition is appropriate, because I believe that presupposition in natural language plays
the same role as preconditions in mathematics or computer science. If the presupposition is not
ful(cid:12)lled, the expression or program becomes meaningless. It is uninterpretable or unexecutable;
the result of the calculationor programbecomes unde(cid:12)ned.
p
(11) a. f(x)= x presupposes that x(cid:21)0
b. for i := 1 to 100 do
begin array[i] := get record(a file)
end
presupposes enough memoryfor a 100 records at the array'saddress
3 Presupposition Projection
Characteristic(ii) obviouslyraisesthe questionunder what circumstancesa presuppositionalele-
ment will or willnot be preserved in a complex sentence. In other words: how can the presuppo-
sition of a compound sentence be determined given the presuppositions of its parts? This problem
has been studied as the Projection Problem for Presuppositions.
Karttunen[30]hasacompositionalmechanismfordeterminingthepresuppositionofacompound
sentence. It depends on three features of constituents: semantic content, presupposition triggers
and the (cid:12)ltering conditions of several embedding operators. There are three kinds of embedding
operators: plugs that block all presuppositions (e.g. indirect speech, say , claim, tell), holes
that let through allpresuppositions(e.g. :, modaloperators likepossibly and most propositional
attitudes) and (cid:12)nally (cid:12)lters that preserve a presupposition depending on the application of the
(cid:12)lteringconditionson the logicalform of a sentence. (e.g. ^;_;!)
The (cid:12)ltering conditions predict when a presuppositional element will be preserved in the com-
pound sentence. This is the natural way of approaching presuppositions from the standpoint of
a compositionalgrammar. The lexiconcontainsthe semanticcontent and informationabout pre-
suppositionsof expressions. The grammarcombinesexpressions. The meaningof a grammarrule
(e.g. some logicalconnective) speci(cid:12)es how the meaning of the expressions is to be combined. It
would be natural to suppose that the connective also speci(cid:12)es whether the presupposition of the
expressionsistobepreservedinthecombination. Iwilldiscussthethreemainlogicalconnectives
9
_;^;!.
Consider implication. Both the presuppositional elements from the antecedent and from the
consequentarepreserved,providedtheyarelogicallyindependent. So(12a)and(12b)presuppose
9Incidentally, (cid:12)ltering conditions use the same concept as strictness analysis from the theory of functional
languages. (Bird and Wadler[7]) An n-ary functional operator f is called strict in its k-th argument i(cid:11) 8xi (1 (cid:20)
i (cid:20) n) fx1::xk(cid:0)1;undefined;xk+1::xn = undefined. A strict function is one that preserves unde(cid:12)nedness. So
functionsthatarestrictinallargumentsareholes. Strictnessanalysisisusedintheparallelexecutionoffunctional
programstodetermine whenitissavetosparko(cid:11)aparallel subprocess.
6
(12d).
(12) a. If baldness is hereditary , most of Jack's childrenare happy.
b. If all of Jack's children are bald, baldness is hereditary.
c. If Jack has grandchildren,his childrenwillbe happy.
d. Jack has children.
But if there is a logical dependency, presuppositions can be blocked or cancelled. In (12c) the
presupposition is already entailed in that context by the antecedent and therefore blocked. Con-
junction behaves in a similarway: presuppositionsfrom both conjuncts are preserved, unless the
(cid:12)rst conjunct alreadyentails the presupposition.
de(cid:12)nition 2 (presupposition projection !;^)
For all (cid:30), if (cid:30) is of the form (cid:30)1^(cid:30)2 or(cid:30)1 !(cid:30)2, then for some context c
a: if(cid:30)1 presupposes (cid:31); then(cid:30) presupposes (cid:31)
b: if(cid:30)2 presupposes (cid:31); then(cid:30) presupposes (cid:31) unless c[f(cid:30)1gj=(cid:31)
Fordisjunctionitismoredi(cid:14)cult. Again,iftherearenologicalrelationsboththepresuppositions
of the (cid:12)rst and of the second disjunct are preserved.
(13) a. Either baldness is not hereditaryor allof Jack's childrenare bald.
b. Either all of Jack's children are bald or baldness is not hereditary.
c. Jack has children.
But for the cancelling cases two di(cid:11)erent de(cid:12)nitions are plausible. A symmetric and a non-
symmetric account. The non-symmetric account is motivated by the by now familiar exam-
ple.
(14) a. Either Jack has no children or all of Jack's childrenare bald.
b. Either all of Jack's children are bald or Jack has no children.
(14a) as a whole does not presuppose that Jackhas children. Apparently the presuppositiongets
cancelled if the negation of the (cid:12)rst disjunct already impliesthe presupposition. That makes the
conditionfor disjunctionanalogousto that for implication,since (cid:30)! $:(cid:30)_ . If disjunction
were completely analogous to implication, (14b) would have to be as strange as `If all of Jack's
10
childrenarebald,then Jackhaschildren.' Indeed (14b)isstrange,but not convincingenough.
Karttunen is wellaware that there are versionsof (14b) that are sensible. Consider a lovingwife
that has not receivedany letters from her Jack. (Karttunen [30] p. 180, note11)
(15) a. Either allof Jack's letters have been held up, or he has not written any.
b. Either Jack has not written any letters or allof them have been held up.
If example (15a) is sensible , and I believe it is, then it does not presuppose the existence of any
letters. It behaves just like (15b) which has the order reversed. That suggests symmetry. So in
that case a presupposition may get cancelled if it is entailed by the negation of the (cid:12)rst disjunct
or by the negation of the second disjunct. This is the symmetric account.
de(cid:12)nition 3 (presupposition projection _ (non-symmetric))
For all (cid:30), if (cid:30) is of the form (cid:30)1_(cid:30)2, then for some context c
a: if(cid:30)1 presupposes (cid:31); then(cid:30) presupposes (cid:31)
b: if(cid:30)2 presupposes (cid:31); then(cid:30) presupposes (cid:31) unless c[f:(cid:30)1gj=(cid:31)
10The reason this is strange, is because the consequent is already presupposed by a trigger in the antecedent.
Theimplication itselfbecomesempty.
7
de(cid:12)nition 4 (presupposition projection, _ (symmetric))
For all (cid:30), if (cid:30) is of the form (cid:30)1_(cid:30)2, then for some context c
a: if(cid:30)1 presupposes (cid:31); then(cid:30) presupposes (cid:31)
b: if(cid:30)2 presupposes (cid:31); then(cid:30) presupposes (cid:31)
unless either c[f:(cid:30)1gj=(cid:31)orf:(cid:30)2gj=(cid:31)
The choicebetween the symmetricornon-symmetricaccountsof disjunctionhasnot been settled
in the literature. I willchoose the non-symmetricaccount because it combinesbest with the rest
of the paper. Important is that disjunction is treated like implication.
Although the projectiontheory is an improvementfromthe purelysemantictheory, somethingis
lost as well. Presuppositionsare reduced to lexicallybased pieces of information that get passed
onornot. Thenotionofapresuppositionasapreconditionislost. Moreover,thetheorydoesnot
explainoreven makeplausiblewhysomeoperatorturns out to be aholewhileanotherisa (cid:12)lter.
Gazdar [18] shows that most plugs `leak'. (see section 5)
4 Pragmatic Presupposition
So far I have stressed the linguistic side of presuppositional inference: there is a certain class of
linguisticconstructions, triggers, that license presuppositionalinference. But why would triggers
carry a presupposition? Why might presupposition be useful in communication? The answer
lies, I think, in a pragmatic view on conversation. (e.g. Stalnaker [43], Lewis [34]) Roughly the
answer will be that presuppositions are presumed to be in the context already. Before I discuss
the pragmatic view on presupposition, I (cid:12)rst need to explain two auxiliary notions: the Gricean
maximsconstrainingcooperativeconversationand a proper notion of context.
cooperative conversation
In [21] Grice formulates a number of maxims that constrain the contributions to a conversation.
Theargumentrunsasfollows. Allparticipantsinaconversationrecogniseacommonpurpose,for
instance to exchange as much information as possible, or to have a lively discussion. In order to
achieve this common purpose, some contributions to the conversation are unsuitable. According
to the cooperative principle allcontributionsare to be madeas requiredfor the currentstage and
purpose of the conversation. The cooperativeprincipleislaiddown in the followingfour maxims.
de(cid:12)nition 5 (Gricean Maxims)
Quantity Make your contribution as informative as is required,
but do not make it more informative than is required.
Quality Make your contribution one that is true:
a. Do not say what you believe to be false
b. Do not say for what you lack adequate evidence.
Relation Be relevant.
Manner Avoid obscurity and ambiguity, be brief and be orderly.
These maxims have two aspects: (i) in speaking one ought to conform to the constraints and
(ii) in understanding one already assumes that speaker conforms to the constraints. Because
of this assumption conversational contributions may carry so-called conversational implicatures:
inferences that exploit the maxims. There are also implicatures arising from a third aspect. If
the speaker obviously violates a maxim, there must be a conversational reason. For example, if
somebodyrudelychangesthesubject,violatingRelation,thisimplicatesthattheprevioussubject
is not to be talked about. Such implicatures are called (cid:13)outing implicatures. Flouting plays no
further role in this thesis. Examples of the (cid:12)rst kind of conversational inference are clausal and
scalarimplicatures.
8
ScalarimplicatureshavetodowiththemaximofQuantity. Formulationscanbeorderedonascale
of informational strength. Saying that Mary and John had an argument is weaker than saying
they had a (cid:12)ght. Formally a scale is a sequence of expressions he1:::eni such that ei j= ej for all
i;j such that j <i. Otherexamplesofscalesareh1;2;3;::i;h_;^i;hmost;alliandhbelief;knowi.
ByQuantitythe higherup the scalethe better. Sowhen the speakerchoosesaweakformulation,
thisimplicatesthathedoesn'tbelievethestrongformulationtobelicensed. Soei implicatesthat
ej is not known by the speaker. (j <i).
Clausal implicatures connect to the maxim of Quality. When the speaker chooses to say for
instance `if (cid:30) is the case, then ...', or `probably, maybe, possibly, I don't know, may or might (cid:30)',
heindicatesthatheisnotsureof(cid:30). SuchconstructionsweakenthespeakersobligationtoQuality.
So probably(cid:30) means that (cid:30) is not known by the speaker.
What occurred to me, was that a similar line of argument can be set up to explain presupposi-
tions as a form of conversational inference. Presuppositions, in a way, connect to the maxims of
Quantity and Relation. We should be both informative and relevant. So we must give new infor-
mation,withoutstatingtheobvious. Thereforeweneedtorefertooldinformation,toembednew
11
information in and also leave out obvious information. My observation is that presupposition
triggers conventionallymark information that is assumed to be uninformative: it ought to be in
the context already. In this way they make languageuse moree(cid:14)cient.
I will distinguish two types of presupposition, arising from the di(cid:11)erent functions they have in
conversational practice. On the one hand we have the existential presuppositions, induced by
12
inde(cid:12)nites,quanti(cid:12)ersand propernames. Thesepresuppositionsmakeitpossibletorefer back
to topics introduced earlier in the discourse. For instance, in choosing to use the man, I am able
torecallforyoualltheinformationaboutsomemanthatappearedinpreviousdiscourse,without
having to restate it.
Ontheotherhandwehavethefactivesandlexical presuppositions. Ibelievethesepresuppositions
leave out information, that has become obvious or easily inferable, by way of world knowledge,
commonsense and the meaningof the concepts involved. Take the wellknown case of the factive
verbregret. Itdoesn'tmakesenseforsomebodytoregretsomethingthathasnoteventakenplace.
Likewise, lexical presuppositions are part of the meaning of the concepts involved. It is di(cid:14)cult
to mark the boundary between lexical presupposition and inference from common knowledge in
general. Comparethefollowingtwoexamples. In(16a)theconceptwidower lexicallypresupposes
masculinityandadulthood. In(16b)thisinformationisnormallyinferredfromcommonknowledge
13
about the Roman Catholic Church. The processes at work do not seem to be much di(cid:11)erent.
In both cases a continuationwith she is wrong or odd.
(16) a. Hillaryis a widower. *...she is very pious.
b. Hillaryis a bishop. ? ...she is very pious.
Fortunately there are presuppositiontests: embed the expression under negation or under maybe
and see if the inference is preserved. In (16a) it should be preserved and in (16b) it should
not.
(17) a. Maybe Hillaryis a widower. * ... she is very pious.
b. Maybe Hillaryis a bishop. ... she is very pious.
In (17b) one could easily come up with some reason to explain the oddity: `Maybe she is in the
Church of England?'. In(17a) continuingwith she remainswrong.
Stillthe exampleshows that there is a very thin line between presuppositionsand other forms of
defeasible conversational inference. Judging the examples becomes a matter of taste. There are
11AlongwithGazdar[18]
12Andindeedpronominal anaphora,asconvincingly shownbyVanderSandt[38,39]. Seesection 7
13NotethatthenameHillarydoesnothavegenderconnotations.
9