Temporal Connectives in a Discourse Context 
Alex Lascarides and .\]on Oberlander* 
Centre for Cognitive Science and 
Human Communication Research Centre, 
University of Edinburgh 
2, Buccleuch Place, Edinburgh, EH8 9LW 
Scotland, UK 
alex, j on@cogsci, ed. ac .uk 
Abstract 
We examine the role of temporal connec- 
tives in multi-sentence discourse. In cer- 
tain contexts, sentences containing tempo- 
ral connectives that are equivalent in tem- 
porai structure can fail to be equivalent in 
terms of discourse coherence. We account 
for this by offering a novel, formal mech- 
anism for accommodating the presupposi- 
tions in temporal subordinate clauses. This 
mechanism encompasses both accommoda- 
tion by discourse aftachme,f and accom- 
modation by temporal addition. As such, 
it offers a precise and systematic model of 
interactions between presupposed material, 
discourse context, and the reader's back- 
ground knowledge. We show how the re- 
sults of accommodation help to determine 
a discou~e's coherence. 
1 Introduction 
We focus on aspects of the discourse behaviour of 
the temporal connectives before, after and when. In 
particular, we note that discourse context can cause 
sentences which are equivalent in temporal structure 
to fail to be equivalent in terms of discourse coher- 
ence. We attempt to explain why context can have 
this effect. The explanation hinges on the differing 
presuppositions posted by the differing connectives, 
and on the novel mechanism whereby background 
knowledge determines how they are accommodated 
into the discourse Structure during interpretation. 
*The support of the Science and Engineering Research 
Council through project number GR/G22077 is grate- 
fully acknowledged. HCRC is supported by the Economic 
and Social Research Council. 
2 Temporal Equivalence and 
Discourse Incoherence 
First, then, consider the following actual sequence of 
states and events: in the UK in November 1992, some 
right-wing Tory backbench MPs were objecting to 
government policy over the treaty of Maastricht, and 
threatened to vote against it; the Prime Minister, a 
Mr John Major, offered them a variety of concessions 
to win them back, in what the press termed a "charm 
offensive"; the MPs responded by voting with the 
government. Call this course of events El. 
We can combine descriptions of the main eventu- 
alities in several ways, to reflect the right temporal 
structure, but only some of these seem pragmatically 
appropriate: consider in particular these possible de- 
scriptions of El involving the connectives before, aft 
fer and tvhe.: 
(1) The backbenchers were in revolt. 
(2) a. They were pacified after Major launched 
a charm offensive. 
b. ?Major launched a charm offensive be- 
fore they were pacified. 
c. They were pacified when Ma- 
jor launched a charm offensive. 
d. ?Major launched a charm offensive when 
they were pacified. 
There are at least two apparent anomalies, which re- 
quire explanation. First, one might expect that (2a) 
and (2b) would be temporally equivalent, both de- 
scribing El; why, then, does (2b) apparently lead to 
discourse incoherence? Secondly, it has been argued 
that A when B permits many possible temporal re- 
lationships between the eventualities denoted by A 
and B (cf. Moens and Steedman 1988); it's for this 
reason that (2c) can be interpreted as denoting El; 
260 
but given this permissiveness, why is (2d) not as ac- 
ceptable as (2c)? 
3 The basic explanation: temporal 
presuppositions 
The basic explanation for the inappropriateness of 
(2b) and (2d) is actually quite simple. Sentences con- 
taining temporal connectives are presuppositional: 
the temporal clause introduces an eventuality that 
must be presupposed to have occurred, for the sen- 
tence as a whole to have a truth-value (cf. Hein~imgki 
1972; Kartunnen 1973). If the presupposed eventu- 
ality is not already in the reader's model of the dis- 
course context, she must add it: a process known as 
accommodation (cf. Lewis 1979). Our view is that 
the discourse behaviour of temporal connectives is 
to be explained as follows. In the discourse context 
where we are describing El, and have uttered (1), 
the way presuppositions are accommodated depends 
on the reader's background knowledge; our inappro- 
priate discourses are precisely those where accom- 
modation ultimately leads to discourse incoherence. 
In particular, the presupposed eventuality from they 
were pacified cannot be accommodated in the previ- 
ous context provided by (1), and must therefore be 
given further treatment. 
A presuppositional explanation stands in contrast 
to the classical accounts of temporal structure built 
upon Kamp's (1981) Discourse Representation The- 
ory (DRT) (cf. Partee 1984; Hinrichs 1986). On both 
these accounts, subordinate clauses, such as those 
introduced by temporal connectives, update the cur- 
rent reference time, and the main clause is then in- 
terpreted with respect to that reference time. How- 
ever, no constraint is placed on the relationship be- 
tween the current reference time, and the new refer- 
ence time supplied by the subordinate clause. And 
so no anomaly will be detected in (2b): a relation 
of temporal progression between (1)'s reference time 
and the new reference time for they were pacified will 
be added to the DRS. Thus, the incoherence of (2b) 
in the discourse context supplied by (1) remains un- 
explained. This is only to be expected, since the 
construction of discourse representation structures is 
syntax-driven, and does not attempt to capture the 
interactions with world knowledge which seem rele- 
vant here. 
So, although it promises to go further, the ba- 
sic presuppositional explanation raises deeper ques- 
tions. Why can't they were pacified be accommo- 
dated into the discourse context provided by (1)? 
What knowledge is it that leads to failure in this 
case, but success when we try to accommodate Ma- 
jor launched a charm offensive? Intuitively, the 
reader's background knowledge affects accommoda- 
tion: world knowledge (WK) and pragmatic maxims 
can make accommodation impossible. 1 So to make 
1 Background knowledge is also essential to the expla- 
the basic explanation precise, we need a formal the- 
ory of how such knowledge constrains accommoda- 
tion. 
Van der Sandt and Geurts (1991) provide a formal 
mechanism for presupposition accommodation in 
DRT, but they provide only informal heuristics that 
stipulate how background knowledge might affect the 
process. We extend their ideas, by providing a for- 
mal specification of those heuristics. We embed their 
account of accommodation in DICE (Discourse and 
C_ommousense Entailment) (Lascarides and Asher 
1991, 1993; Lascarides et al 1992). DICE permits us 
to model the interactions between linguistic knowl- 
edge (LK) and WK which lead to the assignment of 
discourse coherence relations between propositions 
introduced by text segments, and temporal-causal 
relations between the eventualities they denote. The 
primary proposal is that the accommodation of pre- 
suppositions from temporal subordinate clauses be 
modelled as discourse attachment, so that accommo- 
dation is properly constrained by the reader's back- 
ground knowledge. Let us call this basic idea accom- 
modation by discourse attachment (ADA). 
Although we contrasted presuppositional accounts 
with classical DRT approaches, there are clear in- 
stances where a temporal subordinate clause has no 
special rhetorical role in a discourse, but acts in- 
stead as a temporal adverb. Such instances are less 
problematic for classical approaches than cases like 
(1,2b), but at the same time would pose problems for 
an account of temporal connectives that relied ex- 
clusively on ADA. Consider texts (3,4a) and (3,4b), 
modified from Hamann (1989:83-84): 
(3) I'm not a useless driver. 
(4) a. I could drive before you were born. 
b. ?You were born after I could drive. 
(3,4a) and (3,4b) are temporally equivalent, but only 
the former is discourse coherent. If ADA were the 
whole story, then (3,4a) would be analysed as inco- 
herent, since no rhetorical connection can be located 
between the speaker's driving ability and the hearer's 
birth. But (3,4a) is coherent, because the reference 
to birth is simply functioning as an adverbial, locat- 
ing the starting point of driving in the distant past. 
We will therefore suggest that the primary pro- 
posal, where accommodation involves discourse at- 
tachment, must leave room for the possibility that 
presupposed eventualities can be directly added to 
a discourse context, without any discourse relations 
being involved. Let us call this latter idea accommo- 
dation by temporal addition (ATA). Our treatment of 
temporal connectives combines ADA and ATA; it thus 
effectively deals with temporal subordinate clauses 
by bringing together the presuppositional account 
nation of the presuppositions of the counterfactual uses 
of before, first observed by Heingtm~ki (1972:139). We 
have no space to discuss these here, unfortunately. 
261 
and the classical DRT account. We now briefly re- 
view the two basic ingredients of the account: A 
mechanism for presupposition accommodation, and 
a theory of discourse attachment. 
4 A mechanism for presupposition 
accommodation 
Van der Sandt and Geurts (1991) assume that pre- 
suppositions are anaphora with semantic content. 
They distinguish cases in which presuppositions are 
'cancelled' from those in which they are 'realised'. 
The cancelling of presuppositions is explained away 
as binding of anaphora. In other words, cancellation 
occurs when there is an appropriate antecedent in the 
reader's model of the discourse context that can be 
identified with the presuppositional material in the 
clause currently being processed. For example, in 
sentence (5), the presupposition normally associated 
with his wife--which is that John has a wife--is can- 
celled by the conditional clause If John is married, 
which produces an antecedent in the reader's model 
of the context to which his wife can be bound. 
(5) "'If John is married, then his wife will be 
happy. 
The realising of presuppositions is handled through 
accommodation. Suppose there is no appropriate an- 
tecedent in the reader's model of the discourse con- 
text tO Which the presuppositional material can be 
bound. In that case, the reader attempts to add the 
material to the discourse context, subject to certain 
constraints; for example, that the result of the addi- 
tion must be logically consistent. 
Sentences Containing presuppositions are repre- 
sented as a sentence DRS (or SEDRS) which is a triple 
containing: a set of discourse markers; a set of DRS 
conditions; and a (possibly empty) set of SEDRSs. 
The latter set demarcates those parts of the sentence 
that are presupposed, and that must therefore be 
bound or accommodated to the preceding discourse 
context; the former sets are those parts of the sen- 
tence that aren't presupposed. Binding is achieved 
through identifying the presupposed discourse refer- 
ents with those already in the context. Accommoda- 
tion is achieved through adding the presuppositional 
material to part of the discourse context; this process 
is subject to certain informal heuristic constraints. 
Van der Sandt and Geurts provide a definition of 
subordination involving SEDRSs which extends that 
of traditional DRT. A hierarchical structure is thus 
defined, and an order of priority for dealing with pre- 
suppositions can then be specified. The order is: try 
binding at a lower level; binding at a higher level; 
accommodating at a higher level; accommodating at 
a lower level. 
5 A mechanism for discourse 
attachment 
As mentioned before, we wish to enrich van der Sandt 
and Geurts' process of accommodation by using a 
general theory of discourse attachment; by doing this 
we provide a formal specification of the constraints 
on accommodation imposed by the reader's back- 
ground knowledge. The general theory of discourse 
attachment we will use is DICE. 
DXCE rests on a semantically-based theory of dis- 
course structure called Segmented DRT (SDRT) (of. 
Asher 1993). SDRT starts with traditional VltSs (cf. 
Kamp 1981), but goes on to assume with Grosz and 
Sidner (1986) that candidate discourses possess hi- 
erarchical structure, with units linked by discourse 
relations modelled after those proposed by Hobbs 
(1985) (cf. also Mann and Thompson 1987, Scha 
and Polanyi 1988). The resultant representations 
are called segmented DRSs (or SDP.Ss). Here, we use 
five discourse relations: Narration, Background, Re- 
sult, Explanation and Elaboration. The latter two 
are subordinating relations, and the proposition in- 
troduced by the current sentence can attach only to 
the previous constituent of the SDRS for the text so 
far, or constituents it elaborates or explains. 
SDRT defines those parts of an SDRS that are avail- 
able for attachment with new information via a dis- 
course relation. DICE is a logical theory of discourse 
attachment, which explains how to infer which dis- 
course relation to use. DICE specifies rules that rep- 
resent the reader's background knowledge, and these 
interact via the nonmonotonic logic Commonsense 
Entailment (cE) proposed by Asher and Morreau 
(1991), to determine the discourse relations between 
propositions introduced in a text, and the temporal 
relations between the eventualities they describe. We 
here indicate some plausible rules and the inference 
patterns validated by cE, and demonstrate how they 
are involved in discourse attachment. 
The rules that capture WK and LK allow us to rea- 
son about the value of the update function (r, a,/3), 
meaning "the representation 7" of the text so far (of 
which a is already a part) is to be updated with 
the representation/3 of the current clause via a dis- 
course relation with c?'. Let ea be a term referring 
to the main eventuality described by the clause a; 
and let revolt(b,e~) mean that this eventuality is a 
backbencher revolt. As usual, we represent the de- 
feasible connective as a conditional >. The followin~ 
schemas are some rules for calculating implicatures:" 
• Narration: 
(v, a,/3) > Narration(a,/3) 
• Axiom on Narration: 
Narration(a,/3) --+ ea ~ e~ 
2ca abbreviates me(a), which is formally defined in 
Lascaxides and Asher (1993). The indefeasible rules axe 
necessary; we have here omitted the D operators. 
262 
• Result: 
( r, a, \[3) A cause(co, ea ) > Result(a, \[3) 
• Axiom on Result: 
Result(a, \[3) ~ ea -~ e~ 
• States Overlap: a 
(r, a, \[3) A state(e~) > overlap(e~, ea) 
. Background: 
(r, a, \[3) A overlap(e~, ca) > Background(a, \[3) 
• Axiom on Background: 
Background(a, \[3) ~ overlap(ca, e# ) 
• Revolt Law: 
revolt(b, el) A pacified(b, ei ) > -~overlap(el , ei) 
• Charm Law: 
(1", a, \[3) A charlTl(a, b, el) A pacified(b, ei) 
> cause(el, ei) 
• Causes Precede Effects: 
cause(•i, el) --~ -el -~ e2 
Narration, Result and Background represent de- 
feasible LK, and the axioms on them indefeasible LK. 
In particular, Narration and its axiom let us say that 
by default, the descriptive order of events matches 
their temporal order in interpretation. The Revolt 
Law and the Charm Law are slightly different kinds 
of knowledge. The former is pure WE; normally an 
entity isn't revolting and pacified at the same time. 
The latter is a mixture of LK and WK; given that 
the clauses are discourse-related somehow, the events 
they describe must normally be connected in some 
temporal-causal relation; here, charmings normally 
stand in a causal relation to the state of pacification. 
That Causes Precede their Effects is indefeasible wE. 
We also assume that certain discourse relations 
impose various constraints on the topic structure of 
the discourse (el. Asher 1993, Lascarides and Asher 
1993). For example, Distinct Common Topic for 
Narration and Background states that if a and \[3 
form a narrative or background, then they must have 
a distinct, common (and perhaps implicit) topic 7: 
• Distinct Common Topic for Narration and 
Background: 
Narration(a, \[3) V Background(a,/3) ---* 
(=17)(3' # aA7 ¢ \[3A7   aA7 ~\[3) 
cg supports the three patterns of nonmonotonic 
inference that are relevant here. The first is De- 
feasible Modus Ponens: if one default rule has its 
antecedent verified, then its consequent is defeasi- 
bly inferred. The second is the Penguin Principle: 
if there are conflicting default rules that apply, and 
the antecedent of one entails that of the other, then 
the consequent of the more specific rule (the former 
one) is defeasibly inferred. The third is the Nixon 
Diamond: no conclusion is drawn if there are con- 
flicting default rules that apply whose antecedents 
aren't logically related. 
SThere are two versions of this rule; the other covers 
the cases where the second clause is stative. 
To see how the rules work, consider (6) and (7). 
(6) The backbenchers were in revolt. Major 
launched a charm offensive. 
(7) ?The backbenchers were in revolt. They were 
pacified. 
In interpreting (6) we try to attach the second sen- 
tence to the first (so (a, a, \[3) holds, where a and 
\[3 are respectively the logical forms of the first and 
second clauses). Two of our defensible laws apply: 
Narration and States Overlap. They conflict, but 
States Overlap is more specific. So by the Pen- 
guin Principle, overlap(ea, e~) is inferred. So Back- 
ground, which also conflicts with Narration, applies. 
By the Penguin Principle again, Background(a, \[3) is 
inferred, since Background is more specific2 Thus 
(6) is discourse coherent, in the precise sense that \[3 
can be attached to a with a discourse relation; we 
have also found that the state of revolt overlapped 
with the event of Mr Major's charm offensive. 
Now consider (7). The appropriate knowledge base 
in the analysis of (7) satisfies States Overlap, the Re- 
volt Law and Narration. The first two of these con- 
flict, but their antecedents aren't logically related. 
For note that unlike the Charm Law, the Revolt Law 
does not require the clauses concerned to be dis- 
course connected somehow: being pacified and be- 
ing in revolt don't normally overlap, regardless of 
whether they are connected or not. Because there 
is conflict among defeasible rules with unrelated an- 
tecedents, a Nixon Diamond crystallises. Conse- 
quently, no temporal or discourse relation can be in- 
ferred, and so no representation of (7) is constructed, 
leading to discourse incoherence. 
6 The proposal: accommodation by 
discourse attachment 
The basic explanation of the defectiveness of (ib,d) 
relied on the idea that temporal clauses are presup- 
posed; even though (ib) may be taken to refer to 
the same temporal structure E1 as (is), it is prag- 
matically inappropriate. In making this explanation 
more precise, we wish to characterise presupposition 
accommodation as a process of discourse attachment; 
and failure to accommodate thus involves failure to 
attach, or, in other words, (local) discourse incoher- 
ence. In the (1,2) examples, failure to attach at a 
particular site can be fatal, as we will see shortly. 
More precisely: (i) Subordinate temporal clauses 
are presupposed. (ii) If binding the presupposition 
fails, then it must be accommodated. (iii) If accom- 
modation is necessary, then it is assumed in the first 
instance that the proposition introduced by the sub- 
ordinate clause plays a rhetorical function in the dis- 
4Although the double application of the Penguin Prin- 
ciple, as in (6), is not valid in general, Lascarides and 
Asher (1993) show that for the particular type of case 
considered here, CE validates it. 
263 
course, and so accommodation proceeds via discourse 
attachment. The presupposition must be attached to 
the discourse structure by a discourse relation, before 
the DRS of which it is a sub-part is attached. (iv) In 
that case, the presupposition can be discourse related 
to: either prior discourse or the D~S corresponding 
to its matrix clause. (v) If, on the other hand, ac- 
commodation via discourse attachment fails, then 
the assumption that the subordinate clause plays a 
rhetorical role is defeated, and accommodation is at- 
tempted via the addition of the presupposed event 
to the discourse context. (vi) If the presupposition 
is successfully dealt with, an attempt is then made to 
discourse-relate the resulting constituents of the dis- 
course, using the reader's background knowledge. 5 
So, presuppositions can lead to incoherence in at 
least four ways. First, binding may be successful, but 
the resultant constituents of the discourse may fail to 
attach together (as in (3,4b)). Secondly, binding may 
fail, while ADA is successful, and then the resultant 
constituents of the discourse may fail to attach to- 
gether (as in (1,2b)). Thirdly, binding and ADA may 
fail, while ATA is successful--as in (3,4a)--but then, 
in contrast to (3,4a), the resultant constituents may 
fail to attach together. Finally, binding and both 
types of accommodation may fail. 
To reflect this process of interpreting temporal 
connectives in a discourse context, we propose that 
discourse attachment be split into four stages, of 
which the third has three main parts: 
1. We build the sentence DRS (or SEDRS) for the 
sentence containing the temporal connective. 
2. We then calculate the temporal implicatures for 
the SEDRS, that arise from the temporal connec- 
tive used, if there are any. 
3. We then handle the presupposition: (a) We at- 
tempt to bind. If that fails, (b) we attempt ac- 
commodation, by attempting discourse attach- 
ment between available SDRSS and the third sub- 
part of the SEDRS (which corresponds to the pre- 
supposed clause). If the presupposition is bound 
or accommodated by discourse attachment, we 
go to (4). But if (b) fails, then (c) we attempt 
accommodation by adding the third sub-part of 
the SEDRS to an available SDRS, and if this is 
possible, we go to (4). If (c) fails, then we fail 
on the grounds of incoherence. 
4. Attempt discourse attachment between the cur- 
rent DRS and available SDRSs. If attachment suc- 
ceeds, go to (1) with the next sentence. If not, 
fail on the grounds of incoherence. 
5Points (iii) and (iv) correspond to ADA; point (v) to 
ATA. 
7 Temporal information from 
connectives 
First of all, we register Hamann's (1989:76) obser- 
vation that before and after operate on points by 
placing in the SEDRS the relevant precedence condi- 
tions on the points of time at which the eventualities 
are asserted to hold. We fold states into this picture 
by introducing a default 'inceptive' reading for tem- 
poral connectives; corm here varies over before and 
after; an eventuality is incstate if it's inceptive. That 
is, incstate(e6) is true only if the time discourse ref- 
erent t introduced in the DRS 6 is the time where e6 
starts. 
• Inceptiveness with Connectives (lCl): 
= conn(~, 7)^ state(e,) > incstate(e,) 
• Inceptiveness with Connectives (IC2): 
= conn( , ^ aa e(e ) > incstate(e ) 
In words, 6 before/after 7 normally entails that 6 and 
7 are to be interpreted inceptively, if either of them 
are stative. 
It is suggested that when clauses, by contrast, do 
not implicate inceptiveness; indeed they do not have 
any special temporal implicatures (cf. Moens and 
Steedman 1988). However, it can be argued that 
when does have a causal implicature: it serves to re- 
strict the kinds of contingency relationships that can 
hold between eventualities; in particular, it defeasi- 
bly cuts off one possibility: 
• No Cause: when(oh ~) > -.cause(ea, e~) 
8 Worked examples 
To demonstrate how the approach works, we here 
treat several types of cases involving presupposition 
accommodation: first, we deal with two pairs of cases 
where accommodation via discourse attachment suc- 
ceeds; in one pair the result is coherent, and in 
the other it isn't. Then we will deal with a case 
where binding and accommodation by discourse at- 
tachment fail, but accommodation by temporal ad- 
dition succeeds. Finally, we will deal with a case 
where the presupposition is bound. The coherent 
cases treated here are (1,2a) and (1,2c), involving 
after and when and (3,4a), involving before; the in- 
coherent cases are (1,25) and (1,2d), involving before 
and when, and (3,4b), involving after. 
8.1 Discourse attachment with coherence 
Consider text (1,2a): 
(1) The backbenchers were in revolt. 
(2) a. They were pacified after Major launched 
a charm offensive. 
Let the logical representation of (1) he a, and the 
SEDRS for (2a) be ~a; note that the precedence con- 
dition ts -~ t2 is incorporated into the DRS for the 
matrix clause. 
264 
C a) \[el,tl\]\[ revolt(b, el),hold(ex,tl),tl -4 now\] 
(jSa) ({e2, t2}, {pacified(b, e2), hold(e2, t2), 
t2 -4 now, ta -4 t2}, 
({ca, t3}, {charm(a, b, es), hold( e3, ts ), 
t3 -4 now}, ¢)) 
In the first stage of discourse attachment, we build 
the representation for/~a just given. In the second 
stage, we add its temporal implicatures. By IC1, we 
come to believe via Defeasible Modus Ponens that 
the state of pacification doesn't just hold at t2; it 
starts there. 
In the third stage, we attempt to deal with the 
presupposed part of/~,. Let 7 be the presupposi- 
tional clause corresponding to ea, and 6 the matrix 
corresponding to e2. 7 will fail to bind to a. Can it 
attach? We assume (or, a, 7), and so the line of rea- 
soning is exactly that used for (6), and a Background 
relation holds between the revolt and the charm of- 
fensive. Once 7 has been attached, we move on to 
the final stage of processing: we must attach the DRs 
which remains when 7 has been deleted from it. Call 
this e. 
(e) \[e2, t~\]\[pacified(b, e2), hold(e2, t2), t2 -4 now, 
ts -4 t2\] 
The only open constituent in the SDRS built so 
far is 7, because the relation in the SDRS is 
Background(a, 7). So we assume (r, 7, e), and find 
that Narration, States Overlap and the Charm Law 
apply. States Overlap conflicts with what has al- 
ready been accepted via Ic1. Furthermore, it con- 
flicts with the Charm Law, which is more specific. 
So, cause(e3, e~) and Narration(7, e) are inferred. By 
the causal relation, the antecedent to Result is now 
verified, and so Result(7, e) is also inferred. So, in 
brief, the first state functions as background to the 
presupposed event, of which the second sentence's 
state is the result. 
Of the versions of (2) involving the connective 
when, only one is coherent in the discourse context, 
and its analysis is very similar to that of (2a) just 
given. 
(1) The backbenchers were in revolt. 
(2) e. They were pacified when Ma- 
jor launched a charm offensive. 
Just as with (2a), the presupposed charm event is 
successfully accommodated with respect to the pre- 
ceding discourse, and the main clause state of paci- 
fication is then attached as its result. There are two 
differences in the analysis: the semantics of when 
places no conditions in the matrix clause ~ on the 
temporal relation between e2 and ca; however, in the 
second stage of discourse attachment, further impli- 
catures are added (-~cause(e~,e3): the pacification 
did not cause the charming). In spite of these tem- 
poral differences, the final discourse structure is the 
same. 
8.2 Discourse attachment without 
coherence 
Now, let us consider two cases where accommoda- 
tion doesn't ultimately deliver a coherent discourse. 
In both of these cases, accommodation fails with re- 
spect to the previous discourse context, but then suc- 
ceeds within the sentence. Incoherence only follows 
because the resulting structure cannot finally be at- 
tached to the previous discourse context. 
First, take (1,2b). 
(1) The backbenchers were in revolt. 
(2) b. ?Major launched a charm offensive be- 
fore they were pacified. 
We have observed that (2b) denotes the same tem- 
poral structure as (2a), but that it seems incoherent 
in the context of (1). Here, we provide one way to 
account for why the presupposition fails. 
The SEDRS corresponding to (1) is a and the SEDRS 
for (25) is &. 
(fib) ({Ca, t3}, { charm(a, b, as), hold(es, t3), 
ts -4 now, t3 -4 t2}, 
({e2, t2}, {pacified(b, e2), hold(e2, t2), 
t2 -4 now}, 0)) 
In the first stage of discourse attachment, we build 
the representation for /~b just given. In the second 
stage, we add its temporal implicatures. By IC2, we 
come to believe that the state of pacification doesn't 
just hold at t2; it starts there. 
In the third stage, we attempt to deal with the 
presupposed part of /~b. Let 7 be the presupposi- 
tional clause corresponding to e2 (the pacification), 
and 6 the matrix corresponding to ea (the charm- 
ing). 7 will fail to bind to a. Can it attach? We 
assume (a, a, 7), and so the line of reasoning is ex- 
actly that used in (7), and so no discourse relation 
can be found. 
Having failed to attach the presupposition at the 
higher level, we attempt to attach it to its own ma- 
trix clause. We assume (r, ~, "r), and find that Narra- 
tion, States Overlap and the Charm Law apply. The 
Charm Law's conclusion follows by the Penguin Prin- 
ciple, i.e., e3 causes e~; and by a further application 
of the principle, we conclude that a Result relation 
holds between ~ and 7. Call the resultant SDRS e. 
At the final stage of processing, we must attach e 
to the prior discourse--a. Which rules apply when 
attaching e to a? (7", a, e) is added to the reader's KS, 
and so Narration, States Overlap and the Revolt Law 
all apply. To properly discuss this case, we introduce 
here a further law that will apply: one which reflects 
the Gricean maxim 'Be Orderly'. In Lascarides, 
Asher and Oberlander (1992:4-5), we presented a 
rule that constrained orderly text with respect to 
causation: the law reflected the intuition that one 
should not describe things in the order cause-effect- 
further causes of that effect, or effect-cause-further 
265 
effect of that cause. Here, we offer a generalisa- 
tion of this law. Suppose we define two eventuali- 
ties presented in a text as conceptually immediate if 
(a) one causes the other, and (b) the clauses that 
describe them are discourse-related. Then the prag- 
matic maxim below captures the intuition that noth- 
ing described elsewhere in a text should come be- 
tween two conceptually immediate events. 
• Conceptual Immediacy: 
(r, ~, fl) ^ ~ --* Result(v, 8) > -~(e~ -< ibd(e.) -< e6) ^ 
~(e. r -~ fbd(ea) -4 e6) 
In words, Conceptual Immediacy states that if the 
constituent fl is to be attached to a, where/3 contains 
Result(v, 8) (and so e~ causes e6), then the start of 
ea (i.e., ibd(ea)) and the end of ea (i.e., fbd(ea)), 
cannot come inbetween e~ and e6. 
Conceptual Immediacy has an impact on the anal- 
ysis of (2b), because it applies in the attachment 
of e to a, together with the laws we have already 
mentioned. Here, Conceptual Immediacy means that 
normally, the point where the revolt starts or finishes 
cannot come in between the charm offensive and the 
pacification. States Overlap means that normally, 
the revolt overlaps with the event structure described 
in e. So States Overlap and Conceptual Immediacy 
together say that normally, the revolt starts before 
the charm offensive, and continues until at least af- 
ter the pacification has started. But this would mean 
that the revolt and pacification overlap, and this con- 
tradicts the Revolt Law. Thus Conceptual Immedi- 
acy and States Overlap on the one hand, and the 
Revolt Law on the other, are in irresolvable conflict, 
since the antecedents of these laws are unrelated. So 
no conclusions about discourse structure can be in- 
ferred, leading to incoherence. 
Under this analysis, (2b) is coherent in isolation, 
but incoherent in the context of (1). The notion 
of orderliness in discourse plays a crucial role in 
this explanation: eventualities that are causally con- 
nected preclude other eventualities described in the 
discourse from intervening between them. 
The other case of incoherence involves the connec- 
tive when: 
(1) The backbenchers were in revolt. 
(2) d. ?Major launched a charm offensive when 
they were pacified. 
The SEDRS corresponding to (1) is a, and in the first 
stage of processing, we build the SEDRS /~a as the 
representation of (2d): 
(&) ({es,ts}, { charm(., ~, e3), hold(es, t3), 
t3 -~ now}, 
({e2, t2}, {pacified(b, e2), hold(e2, t2), 
t2 ~ now}, ~)) 
In the second stage, we add its temporal implica- 
tures: by No Cause, -~cause(e3, e2) is added to the 
matrix clause 8. This means that the charming 
didn't cause the pacification; apart from anything 
else, this implicature renders (2d) an inappropriate 
vehicle for a speaker who wished to describe the 
course of events E1 we have been discussing. 
In the third stage of processing, as with (2b), both 
binding and accommodating V to a fail, and so we 
assume (1", 6, 7). The laws that apply are: Narration, 
States Overlap and the Charm Law. The Charm Law 
is the most specific, but its consequent is inconsistent 
with what is already known concerning causal struc- 
ture. Thus, States Overlap, which is the next most 
specific law, wins. So we infer Background(8, 7)- Call 
the resultant SDRS e. We must now assume (~, a, e). 
The rules that apply are: Narration, States Overlap 
and the Revolt Law. Notice that in contrast to (2b), 
Conceptual Immediacy no longer applies, because e 
doesn't entail Result(v, 8). Given the temporal struc- 
ture entailed in e, the consequent of States Overlap 
would entail that the revolt and pacification overlap. 
But the Revolt Law entails the opposite. So a Nixon 
Diamond crystallises and the discourse is incoherent. 
~,From examining (1,2b) and (1,2d), it should be 
apparent that managing to accommodate a presup- 
position by discourse attaching it to its matrix is not 
in itself sufficient for discourse coherence. The SDRS 
formed must still be attached within the preceding 
discourse context. It is this second attachment that 
fails to occur in these cases. Both Conceptual Imme- 
diacy and No Cause can yield discourse incoherence. 
In (2d), for example, if it weren't for No Cause, the 
Charm Law would have won during accommodation 
instead of States Overlap. This would have changed 
the set of laws which apply when attaching e to a, 
leading to different inferences about the discourse. 
8.3 Temporal addition with coherence 
Now consider text (3,4a): 
(3) I'm not a useless driver. 
(4) a. I could drive before you were born. 
The logical forms of the two sentences are respec- 
tively a and/~a: 
(or) \[el, tl\]\[-,useless-driver(a, el), hold(el, tl), 
tz -4 now\] 
(#.) ({e2, t2}, {can-drive(a, e~), hold(e2, t2), 
t2 -< now, t2 -< tz}, ({ez, t3}, { born(b, e3), hold(es, tz), 
t3 -< now}, 0)) 
Now, in the first stage of processing, we build the 
SEDRSS just given. In the second stage, we add the 
temporal implicatures, and find that being able to 
drive didn't just hold at t2, it started there. 
In the third stage, we deal with the presupposition. 
Call the third sub-part of the SEDRS ~¢. V can't bind 
to the context, and so we assume (a, a,7), and the 
laws that apply are: Narration and States Overlap. 
But inferring Background via the Cascaded Penguin 
266 
Principle is blocked in this case by WK that con- 
flicts with Background's constraints on topic struc- 
ture: WK dictates that no distinct common topic 
for a being able to drive and b being born can be 
found. Similarly, Narration can't be inferred because 
it imposes the same constraints on topic structure as 
Background. These constraints on topic structure 
explain why the discourse (8) is incoherent. 
(8) ?I'm not a useless driver. You were born. 
So discourse attachment of 7 to a fails. Conse- 
quently, we then attempt accommodation by attach- 
ing 7 to 6 with a discourse relation. This fails for sim- 
ilar reasons: a common topic can't be found. There- 
fore, since accommodation via discourse attachment 
has failed, we attempt accommodation via temporal 
addition. In effect, we try to interpret the subordi- 
nate clause as a temporal adverb, like before 1962. 
We first try to add the discourse referents in 7 and 
their conditions to a: this succeeds, since there are 
no logical inconsistencies. The result is the following 
DRS ~: 
(,) \[el, tl, t \]\[-  seZess-dri er(., el), 
hold(el,tl),tl -~ now, 
born(b, e3), hold(e3, t3), 
t3 -~ now\] 
Having successfully accommodated, we proceed to 
the fourth stage of processing: we attempt to attach 
the matrix clause 6 to e: 
(6) \[e2, t2\]\[can-drive(a, e2), hold(e2, t2), 
t2 -4 now\] 
The rules that apply are: Narration and States Over- 
lap. By the Cascaded Penguin Principle, Background 
is inferred. Note that this time, a common topic can 
be found between the constituents: it is the driving 
ability of a. 
In this example, there was failure to accommodate 
via discourse attachment, but the text was eventu- 
ally predicted to be coherent. This contrasts with 
(1,2b), where accommodation via discourse attach- 
ment was successful, but the text was eventually pre- 
dicted to be incoherent. This indicates that success 
in the early stages of processing doesn't guarantee 
coherence; nor does failure in the first attempt to 
accommodate guarantee incoherence. 
8.4 Binding with incoherence 
We finally provide an example where the presuppo- 
sition is bound, and the resultant discourse is inco- 
herent: 
(3) I'm not a useless driver. 
(4) b. ?You were born after I could drive. 
The SEDRS representing (3) is a above, and the SE- 
DRS representing (4b) is  : 
(/3b) ({e3, t3}, { born(b, e3), hold(e3, t3), 
t3 "~ now, t3 -~ t2}, 
({e2, t2}, {can-drive(a, e~), hold(e2, t2), 
t2 0)) 
In the first stage of processing, we build the SEDRSs 
just given. In the second stage, we add the tempo- 
ral implicatures, and find that being able to drive 
doesn't just hold at t2, it starts there. 
In the third stage, we deal with the presupposition. 
We assume here that the Identify Drive Law forms 
part of the reader's KS: it captures the intuition that 
not being a useless driver and being able to drive are 
one and the same eventuality: 
• Identify Drive Law: 
-useless-driver(a, e) ~ can-drive(a, e) 
Because of the Identify Drive Law, we can bind the 
presupposed material 7 to a. So we then go onto the 
fourth Stage of processing, and attempt to attach the 
matrix clause 6--which represents you were born-- 
to a. By the constraints on topic structure imposed 
by Background and Narration, attachment of 6 to 
a fails, for just the same reasons as it did before. 
Here, in contrast to (3,4a), the violation of the topic 
constraints is fatal, because you were born is a main 
clause. It cannot be reinterpreted as a temporal ad- 
verbial when discourse attachment has failed. 
9 Conclusion 
By concentrating on a simple but pervasive phe- 
nomenon concerning the interpretation of temporal 
connectives, we have extended a formal mechanism 
to show how interacting discourse context, WK and 
LK determine which presupposed eventualities can be 
accommodated. The way in which accommodation is 
handled depends on the content of the presupposed 
clause, and we pointed to some interesting behaviour 
in this connection. 
On the one hand, when accommodation by dis- 
course attachment fails, accommodation by tempo- 
ral addition can still succeed. In such cases, a purely 
temporal reading of the subordinate clause is forced, 
and this leads to very weak coherence constraints for 
the discourse as a whole. These weak constraints 
are akin to those in classical treatments of temporal 
connectives in DRT; however, our analysis still dif- 
fers somewhat, eschewing as it does reference times. 
On the other hand, even when accommodation by 
discourse attachment succeeds, there is no guarantee 
that the text is coherent; presupposition accommo- 
dation is a necessary, but insufficient, part of the 
process of discourse structure retreival. 
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