CONSTRAINTS ON THE GENERATION OF ADJUNCT CLAUSES 
Alison K. Huettner* Marie M. Vaughan ** David D. McDonald ** 
Department of Linguistics * Department of Computer & Information Science ** 
University of Massacusettts Amherst, Massachusetts 01003 
ABSTRACT 
This paper presents an analysis of a family of 
particular English constructions, all of which roughly 
express "purpose". In particular we look at the 
purpose clause, rationale .clause, and infinitival 
relative clause. We (1) show that couching the 
analysis in a computational framework, specifically 
generation, provides a more satisfying account than 
analyses based strictly on descriptive linguistics, (2) 
describe an implementation of our analysis in the 
natural language generation system MUMBLE-86, and 
(3) discuss how our architecture improves upon the 
techniques used by other generation systems for 
handling these and other adjunct constructions. 
1. INTRODUCTION 
Natural language provides a variety of devices for 
expressing relations between elements in a text.. 
Simply positioning two sentences in sequence conveys 
an implicit relation between them: 
(1) I bought a book. I'm going to read it on the plane. 
Clauses may also be joined with explicit lexical 
connectives: 
(2) I bought a book so that I could read it on the plane. 
A few relations may be expressed directly through 
particular types of subordination of one clause to 
another1: 
(3) I bought a book to read on the plane. 
This latter category is the most cohesive of these 
three devices, as the adjunct is crucially dependent on 
the material in the matrix clause for its interpretation 
(Halliday & Hasan, 1976). However, such structural 
linking mechanisms are also the most limited in 
applicability: only certain relations may be expressed 
1 We refer here to infinitive clauses which are grammatically 
related to the main clause as optional adverbials rather than as 
complements (arguments) to a verb, such as "Floyd wanted to 
go to the zoo". 
in this way and complex grammatical constraints must 
be satisfied. 
In this paper, we analyze a particular class of 
structural devices, including the purpose clause 
(exemplified in 3 above), rationale clause, and 
infinitival relative, from the perspective of natural 
language generation. All three constructions express 
kinds of "purpose": purpose clauses express the use to 
which someone will put an object that is expressed in 
the main clause; rationale clauses express the overall 
intention behind the main clause action; infinitival 
relatives express the usual function of their NP head.2 
We look at what underlying semantic relations license 
the constructions, the constraints on the syntactic 
form of the main and adjunct clauses, and the gapping 
pattern of the arguments of each adjunct. We discuss 
these as information needed by the generator in order 
for it to choose and use these devices correctly and 
discuss at what stages in the generation process the 
information must be applied. 
We contrast our analysis with those typically 
given from the perspective of generative- 
transformational linguistics, particularly thematic 
analyses, concluding that an analysis that considers the 
construction in a particular situation and in terms of a 
coherent model of the world can capture the 
constraints more easily. We provide a particular 
example implemented in the natural language 
generation system MUMBLE-86 (McDonald, 1984) 
and show how our analysis may be generalized to 
similar structural adjunct constructions. We further 
show that many earlier approaches to generating 
complex sentences (Derr & McKeown, 1984; Davey, 
1974; Kukich, 1985; Mann & Moore, 1981) have 
architectural limitations that would keep them from 
handling these types of constructions with any 
generality. 
2 The notion of "purpose" is of course ambiguous between 
"intention" and "function". 
207 
2. DESCRIPTION OF THE CONSTRUCTION 
Before addressing the generation of adjunct 
infinitive clauses, it is necessary to define our terms 
and distinguish the different constructions. We will 
begin by discussing purpose clauses 3 and then contrast 
them with rationale and infinitival relative clauses. 
2.1 Purpose clauses 
A purpose clause (PC) expresses the purpose or 
intended use of a particular object which the main 
clause is in some sense "about". It is attached as a 
daughter of VP and is fixed in VP final position. It 
has the following variants, distinguished trivially by 
the position of the gap: 4 
(4) a. I bought the shelfi \[e i to hold my cookbooks\] 
b. I bought the cookies i \[for Mary to eat ei\] 
e. I bought the cushion i \[for Mary to sit on eL1 
The sentences in (4) demonstrate that PC has one 
obligatory gap, which can occur in any of its NP 
argument positions: subject position, as in (a);5 direct 
object position, as in (b); or prepositional object 
position, as in (c). The gap is coreferential with 
CcontroIled by") the direct object of an SVO main 
clause, or with the subject of a passive or unaccusative 
main clause. This pattern of antecedents has been 
variously characterized as deep structure (direct) 
objects (Huettner, 1987; implicitly in Rappaport & 
Levin, 1986); as arguments bearing the thematic role 
of Theme (Faraci, 1974; Williams, 1980); or as 
entities whose availability for further manipulation 
plays a part in the semantics of the sentence (Jones, 
1985). 
A PC with its obligatory gap in non-subject 
position (like those in 4b,c above) may have an 
additional subject gap, as shown in (5): 
(5) lj bought it i \[ej to eat ei\] 
This second gap is optional, and the determination 
of its antecedent is more complex than the controller 
of the obligatory gap. In (5) the PC subject is 
coindexed with the matrix (main clause) subject; 
however, (6) shows that an indirect object takes 
3 The purpose clause has also been known as a "re~oactive 
purpose clause", for example in Jespersen (1940). Jespersen 
reserves the term "purpose clause" for what we are calling a 
rationale clause; however, our terminology dates at least from 
Faraci (1974) and is used by Bach (1982) and Jones (1985) 
among others. 
4 The symbol "e" stands for an empty category, or gap, in an 
argument position. The subscripts indicate coreference. 
5 A PC with a subject gap is often called an objective clause. 
precedence over the subject as controller for tnls gap: 6 
(6) a. I gave it i to Mary k \[e k to read ell 
b. *lj gave it i to Mary k \[ej to read ei\] 
When there is no suitable antecedent in the matrix, 
the optional subject gap will have arbitrary or 
indefinite reference: 
(7) a. This box i was purchased \[ear b to keep supplies in ell 
b. These doughnuts i are \[ear b to eat ell 
The set of antecedents for the optional subject gap 
has been characterized configurationally, as the 
"closest" NP argument after the obligatory gap has 
found an antecedent (Chomsky, 1980) ; thematically, 
as the highest NP argument on a "thematic hierarchy" 
ranging from Goal to "arbitrary" (Nishigauchi, 
1984); and pragmatically, as the person in whose 
control the Theme is at the time of the action 
(Ladusaw & Dowty, 1985). 
2.2 Rationale Clause 
Easily confused with the purpose clause is the 
rationale clause (RatC), also known as an "in order 
to" clause or result clause. RatC can be distinguished 
from PC by the fact that RatC permit only subject 
gaps, whose antecedent is (usually) the matrix 
subject, rather than its object. Note the ambiguity of 
the following: 
(8) Amy Lou i took Mildredj to the zoo ei/j to feed the lions. 
On the PC reading, Mildred is feeding the lions; 
on the RatC reading Amy Lou is feeding the lions 
(possibly using Mildred as lion food). A RatC 
reading may always be paraphrased with in order, as 
in (9), to rule out the PC reading: 
(9) Amy Lou i took Mildredj to the zoo in order el~. j to feed 
the lions. 
In contrast with PC, the controller of a RatC gap 
need not be any argument of the main verb, but can be 
the matrix predicate as a whole: 
(10) Mildred was thrown in the lion cage to keep her from 
talldng. 
6 Notice that in sentences like (6a), it is the status of Mary as 
indirect object which allows it to control the subject gap. Prepositional objects which are not indirect objects cannot be 
controllers here, as shown in (a) below, while indirect objects 
which are not prepositional objects may still control the PC 
subject ((b) below). 
a. Ij got the bonesifrom Paul k \[ej/*k to feed e i to the dog\] 
b. lj gave Mary k this very dull book i \[e*j/k to read ei\] 
208 
Further, the RatC subject gap is optional: 
(i 1) Elroy killed Oscar in order for Sylvia to escape. 
Finally, RatC are daughters of S, and not VP, and 
may therefore be preposed alone (12b) or otherwise 
isolated from the VP (12c): 
(12) a. Helga carries a hat pin to protect herself. 
b.To protect herself, Helga carries a hat pin. 
c.What Helga does to protect herself is carry a hat pin. 
2.3 Infinitival Relative Clauses 
Infinitival Relatives (IR) are superficially very 
similar to purpose clauses, especially in the patterning 
of their gaps. Like tensed relatives, they are 
daughters of NP; if the NP in question is in the VP, 
IR can be easily mistaken for PC: 
(13) a. IR: I bought \[ a pan i \[e to fry omelets in ei\] \] 
b. PC: 1 bought \[ apart i \] \[e to fry omelets in e i 
(14) a. IR: Elroy really needs \[ a woman i \[ e i to hoM his 
hana l l 
b. PC: Elroy really needs \[ a woman i \] \[ e i to hold his 
hand l 
IR, like PC, have one obligatory gap in either 
object (13a) or subject (14a) position, which is 
controlled, not by the matrix object (as in PC), but by 
the head of the NP containing the relative (just as in a 
tensed relative clause). If the obligatory gap is in 
object position, there may or not be a subject gap as 
well. This optional subject gap is controlled exactly 
like the optional gap in a PC. 
An IR may be distinguished from a PC by making 
its containing NP the subject of the matrix sentence; 
PC may not occur in post-subject position. Another 
test is to make pro-nominal or definite the antecedent 
of the obligatory gap; IR may only have indefinite 
heads. 
2.4 What the constructions mean 
Three things are being communicated when one 
uses a purpose clause: an event of acquisition or use, 
an object (the thing which is being acquired or used), 
and the purpose to which the object will be put. That 
these elements form a deliberate complex and are not 
independent is made clear by attempting to omit 
either of the first two elements while retaining the 
syntactic form that gives the purpose clause its special 
character. In (15a), the object is not explicit in the 
matrix clause; in (15b), the matrix does not convey 
any sense of possession. Both are ungrammatical. 
(15) a. *I went to the bookstore to read on the plane. 
b. *Peter read a book for Helga to read on the plane. 
The infinitival relative, in contrast, has only two 
elements: an object and its purpose. Furthermore, 
there is no particular event that this purpose is 
specific to, i.e. no special relationship between the 
matrix clause in which the object appears and the 
purpose expressed by the relative. 7 Consequently, the 
notion of purpose in an IR is narrower than in a PC, 
closer to the object's intrinsic function or unmarked 
use. 
The rationale clause differs from both the PC and 
IR by not being object centered at all. Instead, a RatC 
adjunct expresses the goal which the matrix action 
was intended to bring about. 
Note that as the various types of infinitive clauses 
become less deeply embedded, syntactically speaking, 
the scope of the expressed purpose becomes wider: 
from the standard function of an object, expressed 
within a noun phrase (IR); to the function some agent 
has imposed on an object, expressed in the verb 
phrase (PC); to the intended goal of the agent in 
performing the matrix activity, expressed in an S- 
level adjunct (RatC). 
3. GENERATING THE CONSTRUCTIONS 
To analyse a construction for generation, we must 
consider what it means, or, put another way, consider 
why a speaker would choose to use it, especially given 
the subtleties of meaning that differentiate it from 
similar constructions. The next consideration, and 
the subject of the present section, is how the 
construction should be situated within the generation 
process: what decisions, made at what point or points 
in the process, contribute to the selection and 
realization of the construction as part of an utterance? 
We begin with an overview of how decision making is 
organized in our model of generation. We then look 
at how a descriptive treatment in terms of thematic 
roles could be turned into an algorithm for 
generation, and show that it fails to take advantage of 
the information that is available at the early stages of 
generation. A treatment tailored to generation is 
markedly simpler: creating a PC from a motivated 
message is easier than describing the end product. 
7 An NP containing an infinitival relative clause is characteristically descriptive rather than referential; however, 
this has more to do with the restrictive nature of the relative than 
with the content of the matrix. 
209 
3.1 Decision Making in Generation 
In generation, unlike comprehension, the 
speaker's appreciation of his situation, his goals, and 
the information that he wants to communicate are 
self-evident, rather than needing to be discovered. 
The core problem in generation is making decisions: 
knowing what decisions must be made, what 
information bears on them, what the alternative 
choices are and how they are to be represented. 
Carefully controlling the timing of when specific 
decisions are made offers the possibility of designing 
the generation process so as to achieve a very high 
level of efficiency. Forcing a decision too early 
before all of the information it requires is available 
may lead to guessing and later having to back up and 
undo that choice and any later ones that depended on 
it. Making a decision too late can mean missing 
opportunities to propagate information about the 
choice to other decisions that it should influence. 
Overall, the most pivotal and least constrained 
decisions should be made first, so that their 
consequences can be known soon enough to not hold 
up the others that are dependent on their choices. 
In our model of generation, this criterion has led 
us to the view that decisions about the information an 
utterance is to convey will be made before decisions 
about syntactic form or serial order. These early 
decisions typically include choices of wording and 
influence all aspects of a text's form. The output of. 
such decisions is expressed in an explicit 
representational level we call the "message level" 
(McDonald & Vaughan, 1987). Decisions reflecting 
the surface ordering of the arguments are made in the 
mapping to the next level of representation, the 
surface structure. As this structure is traversed, 
decisions about the particular realization of the 
arguments are made, morphological specialization is 
done, and the text is output. 
3.2 Attempting to Adapt a Descriptive 
Analysis 
In conventional transformational=generative 
analyses, the rules governing the occurrence of gaps 
in the constructions we are studying are characterized 
from a purely descriptive perspective. They do not 
try to determine which argument should be gapped, 
but rather where gaps may occur and what the 
antecedent of each gap will be. Directly adapting such 
an analysis to the generation task would involve 
complete specification of the surface structure 
followed by a multi-step matching algorithm to 
realize the gap(s). 
Of descriptive analyses, those couched in terms of 
thematic roles seem best suited for the generation of 
PC, since they allow a single description of the 
antecedent of the obligatory gap. A possible 
algorithm for locating gaps in PC would be as follows 
(assuming that arguments of the matrix verb are still 
accessible from within the adjunct and are annotated 
with their thematic roles): 
. 
. 
Gap the first argument in the PC which is an 
occurrence of the matrix Theme. 
a. If the PC subject matches the matrix Goal, 
gap it; or 
b. if there is no matrix Goal and the PC subject 
matches the matrix Source or Location, gap 
it; or 
c. if there is no matrix Source or Location 
either, and the PC subject is given as 
"unspecified", gap it. 
While for our purposes such an algorithm is an 
im-provement over a structural description, it is still 
unnecessarily complicated. For instance, there is no 
need to search the matrix clause for its theme since 
when generating we already know trivially which 
argument to obligatorily gap--the one that the 
purpose clause was chosen to express the purpose of. 
3.3 Choosing the construction 
Since, as we have discussed, there are semantic 
differences among PC, IR and RatC, the choice 
among them is more than just stylistically motivated 
syntactic variation. This means that they will be 
distinguished at the message level, since that is where 
an utterance's information content is determined. We 
have also argued that the PC and its matrix clause 
form a conceptual unit centering around the object 
whose use is in question. If that integrity is not to be 
left to chance, that conceptual unit must be chosen as 
a piece, making the PC an atomic resource that the 
English language provides, like adjectives or the 
copular clause. 
At the message level then, we have a three part 
relation embodied in a "realization specification" (see 
example in Section Four), which stipulates that the 
statement of possession or access to an object and the 
statement of the purpose of that object are to be 
realized as main clause and PC respectively, with the 
occurrence of the object in the PC realized as a trace. 
The obligatory gap is thus inserted at the message 
level, and persists into surface structure, where 
realization of the two clauses as active, passive, etc. 
can take place without a subsequent costly calculation 
210 
of which structural position should be realized as a 
gap. (We will discuss the optional gap below). Since 
the tense of the adjunct is left unspecified in the 
realization specification, it will surface as an 
infinitive. 
Delaying the realization of the two clauses until 
the linguistic context governing that realiation has 
been established provides versatility. For example, 
the whole construction could be a complement to 
another verb, as in (16a), or to another infinitival 
adjunct, such as the rationale clause shown in (16b): 
(16) a. I wanted to buy a book to read on the plane. 
b. I went to the bookstore to buy a book to read on the 
plane. 
One potential problem with this analysis is that the 
lack of prior constraint leaves open the possibility of 
generating rather awkward constructions, such as the 
following: 
(17) A book was bought by me to read on the plane. 
It is our intuition, however, that the awkwardness 
of this sentence comes from a lack of motivation for 
the passive rather than any problem with the 
construction as a whole. Without a motivated source, 
this construction would never be generated; 
consequently we need not address how to block it. We 
can use this sort of argument to great advantage when 
working in a generation framework, which is one of 
the reasons why it provides a better model of how 
language is actually produced than the usual linguistic 
strategy of free generation with surface level filters. 
The obligatory gap in the PC can (and should) be 
handled at the message level because (1) at that point 
all the information it requires is available, (2) no 
further information bearing on the identification of 
the argument to be gapped will become available later 
during realization (i.e. there is nothing gained by 
waiting), and (3) the means for carrying out the 
gapping operation are at hand (see next section). The 
optional subject gap is a different matter. This gap is 
licensed only if its antecedent is explicitly mentioned 
in the main clause, a fact that is not known at the 
message level. (More to the point, having known the 
information when the message was being assembled 
was unlikely to have changed the decisions that were 
made; consequently there is no utility to making it 
explicit there.) 
Since the information needed to consider gapping 
the PC's subject is not available until the matrix clause 
has been realized, the gapping operation must be done 
at the level of surface structure rather than the 
message level. By relying on the fact that only well- 
formed, motivated messages are ever going to be 
constructed, a surface-level rule for the operation can 
be compactly stated: "gap if the subject is mentioned 
in the matrix or is arbitrary (and non-emphatic). ''8 
The single gap of a rationale clause is handled 
very much like the optional gap of the purpose clause. 
The planner is responsible for the overall relationship 
between an action and an intended result of that 
action. When the message is converted to a surface 
structure, it is realized as a main and a subordinate 
clause; the main clause, as the head of the bundle, is 
built first, and the RatC is then attached either before 
or after it. During traversal of the tree, the RatC 
subject will be gapped if it matches the main clause 
subject or the main clause as a whole. Once again, the 
information needed to determine whether to gap is 
not available until late in the process. 
4. EXAMPLE 
In this section we describe the particulars of our 
implementation of purpose clauses in the natural 
language generation system, Mumble. As we 
discussed in the previous section, this construction 
originates from a three part relation between an 
event, an object, and its purpose. At the message 
level, the interface to Mumble, the schema shown 
below in Figure One takes these three arguments and 
builds a realization specification for a purpose clause: 
define-specification-schema 
object-centered-event-&-purpose 
(object event object-purpose) 
(let ((matrix (instantiate-specification 
event)) 
(adjunct (instantiate-specification 
object-purpose))) 
(add-further-specification matrix 
:specification adjunct 
:attachment-function 'purpose-of) 
(locate-argument-&-force-to-a-trace 
object :containing-rspec adjunct) )) 
FIGURE ONE 
8 "Emphatic" refers to both marked stress, as in (a), or an unusual situation, as in (b), where the possessor is not the 
intended user: 
a. I bought that dinosaur for me tO play with (so keep your 
off it: ) 
b. I bought David a dinosaur for rne to play with (when 1 go 
over to his house). In a generation model, which assumes the generator is working 
in the service of some coherent underlying program, the 
information of when something is emphatic, or marked, is always know and can be made available to the linguistic 
processes, and would be necessary in any event in order to 
generate speech. 
211 
Figure Two shows the pretty printing of the 
realization specification created by this schema in 
order to generate the following text: 
"Floyd bought Helga a book m read on the plane." 
(event-bundle 
:head ( : realization-fn buy 
I : arguments (#<Floyd> #<Helga> 
#<book> ) ) 
~:accessories ( tense-modal past ) 
: further-specifications 
( ( : specification 
(event-bundle 
:head ( : realization-fn read 
: arguments 
( #<Helga> 
(:trace #<book>)) ) 
: further-specifications 
(#<on-location #<read ...> 
#<plane> > ) 
5- :attachment-fn purpose-of ) ) ) 
FIGURE TWO 
In order to make the example clearer, we have 
used the" short hand notation #< ... > to indicate an 
underlying object from which a specification will be 
planned, rather than writing out its specification in all 
its detail. In the context of an actual underlying 
program generating from internally modeled objects, 
these could be unplanned specifications of objects, 
with planning and realization interleaved. However, 
as this example presently runs in our "stand-alone" 
interface, all the details are spelled out in the 
realization specification. 
The bundle representation allows the planner to 
group component parts of the utterance. The head of 
the bundle (#1) is a constraint expression specifying 
the matrix clause. Accessories (#2) contain 
linguistically marked information, such as tense and 
NP number. The further-specification field (#3) 
specifies the adjunct. Note that the argument for 
#<book> (#4) has already been constrained to be a 
trace. The attachment function (#5) indicates how the 
further specification is related to the head. In this 
instance the attachment function is the particular 
attachment point PURPOSE-OF (shown in Figure 
Three), which splices a new element, labeled FOR- 
INFINITIVE, into the surface structure as the last 
element of the VP. 
(define-attachment-point purpose-of 
:splice 
:reference-labels (vp) 
:link (last) 
:new-slot (for-infinitive) ) 
FIGURE THREE 
Every specification has a realization function and 
a list of arguments. In general, the realization 
function is a class of choices which defines the set of 
initial trees (Joshi, 1985) which can realize the 
specification. The choices are annotated with the 
grammatical and contextual characteristics which 
distinguish their use. For example READ (#6), 
through a curried realization class (shown in Figure 
Four), uses the class AGENT-VERB-THEME 9 
(define-curried-realization-class Read 
(agent theme) 
: class agent-verb-theme 
((verb "read") )) 
(define-realization~class Agent-verb-theme 
(agent verb theme) 
( ((basic-clause-svo agent verb theme) 
(clause) () ) 
((for-infinitive-svo agent verb theme) 
(for-infinitive) () ) 
( (relative-clause-svo rel-pro (agent) 
trace (agent) 
verb 
theme) ) 
(relative-clause) 
(arg-same-as-head(agent)) ) 
((relative-clause-svo tel-pro(theme) 
agent 
verb 
trace(theme)) ) (relative-clause) 
(arg-same-as-head(theme)) ) 
)) 
FIGURE FOUR 
The message is realized in stages. First, the head 
of the bundle (#1) is realized by making a choice in its 
class (similar to that for READ in Figure Four) and 
building the surface structure representation for that 
choice, shown below in Figure Five. 
\[SENTENCE\] 
clause 
~ attachment-point \[SUBJECT\] ~-\[PREDICATEI 
purpose-o! 
#,: FLOYD / vp ~ 
\[VERB\] ~ \[INDIR-OBJI ._t~\[DIR -OBJ\] 
"buy" #,: HELGA ~, #,~ BOOK .~ 
FIGURE FIVE 
9 We use thematic roles as argument names in classes heuristically; we are not committing ourselves at this point to a 
thematic analysis of argument structure. 
212 
The accessories (#2) are then processed, which in 
this example sets the tense. Next the further 
specification is spliced in using the indicated 
attachment point. The surface structure is traversed, 
and embedded arguments are realized as they are 
reached. The result of these operations and the 
traversal up to the subject of the adjunct is shown in 
Figure Six. Note that the text of the main clause has 
been morphologically specialized and output as a side 
effect of the traversal, the surface structure for the 
argument NPs has been chosen and built, and the trace 
for the obligatory gap is already in place. 
At this point the optional subject gap of the 
adjunct is considered. Since "Helga" is available as an 
explicit argument of the matrix clause, the subject is 
realized as a trace and the "for" is supressed. 
5. RELATED WORK IN GENERATION 
Derr & McKeown (1984) directly address the 
generation of complex sentences; however, they 
restrict the criteria for combining propositions to 
focus and shared arguments. While it is fairly clear 
that they could extend their analysis to allow 
combinations based on relations between propositions 
that are expressible as explicit lexical connectives, it is 
unclear as to whether they could as easily extend it to 
relations expressed structurally: They assume that the 
propositions are independently determined before 
possibilities for combinations are considered. While 
a special device could determine whether the 
particular relation licensing a PC was intended, they 
would lose the advantage we gain from letting the 
initial choice of object and construction be made 
simultaneously. They would have to use an algorithm 
such as the one described in the thematic analysis 
above to determine the gapping pattern of the adjunct. 
Davey (1974) and Kukich (1985) both simplify 
their approach to the problem by completely 
predetermining how propositions may be combined 
into complex sentences. Kukich uses predefined 
phrases and Davey a set of rules particular to the 
annotated move list of the tic-tac-toe game he is 
generating from. While these approaches provide an 
opportunity for choosing structures such as purpose 
clauses early and as one piece, they are seriously 
lacking in generality and flexibility. Both assume a 
limited domain where all of the possible propositions 
and their plausible combinations can be 
predetermined. 
In the Knowledge Delivery System (KDS) Mann 
& Moore (1981) use a hillclimbing algorithm to 
determine which propositions should be combined 
into complex sentences. The algorithm assumes the 
information to be conveyed has been broken into 
kernel sized chunks and filtered to delete any 
repetitious or inferable information. This has the 
drawback that once the original information has been 
fragmented into kernels, the original relations 
between them have been lost. The aggregation rules 
must consequently use shared arguments and 
predefined templates to combine the kernels into 
sentence sized chunks. This causes the same problems 
as those described for Derr & McKeown: 
determining the gapping pattern in the adjunct clause 
and retaining generality. 
\[SENTENCE\] 
clause 
\[SUBJECTI --4~ \[TNS\] ~ \[PREDICATE\] <past> 
np S V P ~.,~..,~......,.,..~ 
\[HEAD\] \[VERBI .....~INDIR-OBJ\] ~ \[DIR -OBJ\] 
"Floyd" np b-, j 
\[HEADI 
"Helga" 
Text output so far: 
Floyd bought Helga a book 
\[FOR-INFINITIVE\] 
np clause 
\[HEAD\] 
"book" \[FOR-SUBJECT\] "=---I~\[PREDICATEI 
\[VERB\] .__.~\[DIR -OBJt . . . 
"head" trace 
FIGURE SIX 
213 
6. CONCLUSION 
In this paper we have shown the importance of 
carefully choosing the framework in which to couch 
one's analysis. For the generation of adjunct clauses, 
a computational approach which assumes a coherent 
underlying world model and text planner has clear 
advantages over a descriptive representation. We 
have also shown advantages of our model of 
generation: Our use of a message level distinct from 
and prior to the surface structure representation 
allows decisions to be made when germane 
information is most naturally available. 
7. REFERENCES 
Bach, Emmon (1982), "Purpose Clauses and Control." In 
Jacobson & Pullum, eds., The Nature of Syntactic 
Representation, Reidel, Dordreeht, pp. 35-57. 
Chomsky, Noam (1980), "On Binding." Linguistic Inquiry 
11.1, MIT Press, Cambridge. 
Davey, Anthony (1974), Discourse Production. Edinburgh 
University Press, Edinburgh, U.K. "Using Focus to 
Generate Complex and Simple Sentences." Proceedings of 
Coling-84, pp.319-326. 
Faraci, Robert A. (1974), Aspects of the Grammar of 
Infinitives and For Phrases. MIT Doctoral Dissertation 
(unpublished). 
Halliday, M.A.K. & Ruqaiya Hasan (1976), Cohesion in 
English.. London: Longman Group Ltd. 
Huettner, Alison K. (1987), Adjunct Infinitives: An Exegesis. 
PhD Dissertation, University of Massachusetts, Amherst, 
Massachusetts, forthcoming. 
Jespersen, Otto (1940), A Modern English Grammar on 
Historical Principles. G. Allen & Unwin, London. 
Jones, Charles (1985), Syntax and Thematics of Infinitival 
Adjuncts. Phi3 Dissertation, University of Massachusetts, 
Amherst, Massauchusetts. 
Joshi, Aravind (1985), "Tree Adjoining Grammars: How 
much context-sensitivity is required to provide reasonable 
structural descriptions?" In Dowty, Karttunen, & Zwicky 
(eds.), Natural Language Parsing, Cambridge University 
Press, Cambridge. 
Kukich, Karen (1985), "Explanation Structures in XSEL." 
Proceedings of the 23rd Annual Meeting of the Association 
for Computational Linguistics, pp. 228-237. 
Ladusaw, William & David Dowry (i985), "Towards a Formal 
Semantic Account of Thematic Roles." Unpublished 
manuscript. 
Mann, William & James Moore (1981), "Computer Generation 
of Multi-paragraph English Text." American Journal of 
Computational Linguistics, Vol. 7, No.l, Jan.-Mar., 
pp. 17-29. 
McDonald David D. (1984), "Description Directed Control: Its 
implications for natural language generation." In Cercone 
(ed.), Computational Linguistics, Plenum Press, pp. 403- 
424; reprinted in Grosz, Sparck Jones, & Webber, 
Readings in Natural Language Processing, Morgan 
Kaufman Publishers, California, 1986. 
McDonald David D. & Marie M. Vaughan (1987), "Arguments 
for a Message Level in Natural Language Generation." Submitted to UCAI-87. 
Nishigauchi, Taisuke (I984), "Control and the Thematic 
Domain." Language 60, Linguistic Society of America, Waverly Press, Baltimore. 
Rappaport, Malka & Beth Levin (1986), "What to do with 
Theta Roles." Lexicon Project Working Papers #11, MIT 
Center for Cognitive Science, Cambridge. 
Ritehie, Graeme (1984), "A Rational Reconstruction of the 
Proteus Sentence Planner." Proceedings of Coling-84, pp. 
327-329. 
Williams, Edwin (1980), "Predication." Linguistic Inquiry 
11.1, MIT Press, Cambridge. 
214 
