A Compositional Semantics for Focusing Subjuncts 
Daniel Lyons* 
MCC 
3500 West Balcones Center Drive 
Austin, TX 78759, USA 
lyons~mcc.com 
Graeme Hirst 
Department of Computer Science 
University of Toronto 
Toronto, Canada MSS 1A4 
gh~ai.toronto.edu 
Abstract 
A compositional semantics for focusing subjuncts-- 
words such as only, even, and also--is developed 
from Rooth's theory of association with focus. By 
adapting the theory so that it can be expressed in 
terms of a frame-based semantic formalism, a seman- 
tics that is more computationally practical is arrived 
at. This semantics captures pragmatic subtleties by 
incorporating a two-part representation, and recog- 
nizes the contribution of intonation to meaning. 
1 Introduction 
Focusing subjuncts such as only, even, and also 
are a subclass of the sentence-element class of ad- 
verbials (Quirk et al., 1985). They draw attention 
to a part of a sentence the focus of the focusing 
subjunct--which often represents 'new' information. 
Focusing subjuncts are usually realized by adverbs, 
but occasionally by prepositional phrases. Focusing 
subjuncts emphasize, approximate, or restrict their 
foci. They modify the force or truth value of a sen- 
tence, especially with respect to its applicability to 
the focused item (Quirk et al., 1985, §8.116). 
1.1 The problem with focusing subjuncts 
There are several reasons why developing any se- 
mantics for focusing subjuncts is a difficult task. 
First, focusing subjuncts are 'syntactically 
promiscuous'. They can adjoin to any maximal pro- 
jection. They can occur at almost any position in a 
sentence. 
Second, focusing subjuncts are also 'semantically 
promiscuous'. They may focus (draw attention to) 
almost any constituent. They can precede or fol- 
low the item that they focus, and need not be adja- 
cent to this item. The focus need only be contained 
somewhere within the syntactic sister of the focus- 
ing subjunct. Because of this behavior, it is difficult 
to determine the intended syntactic argument (ad- 
junct) and focus of a focusing subjunct. Sentences 
*The work described in this paper was done at the University 
of Toronto. 
such as those in (1) can be ambiguous, even when 
uttered aloud with intonational effects. 1 
(1) 1. John could also (SEE) his wife from the 
doorway (as well as being able to talk to 
her). 
2. John could also see (his WIFE) from the 
doorway (as well as her brother). 
3. John could also see his wife (from the 
DOORway) (as well as from further inside 
the room). 
4. John could also (see his wife from the 
DOORway) (as well as being able to do 
other things). 
Third, the location of intonational stress has an 
important effect on the meaning of a sentence con- 
taining a focusing subjunct. Sentences may be 
partly disambiguated by intonational stress: inter- 
pretations in which stress falls outside the intended 
focus of the focusing subjunct are impossible. For 
example, the sentence 
(2) *John could also see (his wife) from the 
DOORway. 
is impossible on the indicated reading, since stress 
on door cannot confer focus on his wife. On the other 
hand, stress does not help to disambiguate between 
readings such as (1.3) and (1.4). 
Fourth, focusing subjuncts don't fit into the slot- 
filler semantics that seem adequate for handling 
many other sentence elements (see Section 1.3)~ At 
best, their semantic effect is to transform the se- 
mantic representation of the constituent they modify 
in some predictable compositional way (Hirst, 1987, 
p. 72). 
Finally, focusing subjuncts carry pragmatic "bag- 
gage". The meaning of a focusing subjunct includes 
distinct asserted and non-asserted parts (Horn, 
1969), (Karttunen and Peters, 1979). For example, 
1 In the example sentences in this paper, small capitals de- 
note intonational stress. Angle brackets 0 enclose the focus 
of a focusing subjunct and square brackets \[ \] set off the con- 
stituent to which the focusing subjunct adjoins. Unacceptable 
sentences are preceded by an asterisk. 
54 
(3) asserts (4.1) but only presupposes (4.2) (Horn, 
1969): 
(3) Only Muriel voted for Hubert. 
(4) 1. No one other than Muriel voted for Hu- 
bert. 
2. Muriel voted for Hubert. 
Analogously, (5) asserts (6.1) and presupposes (6.2) 
(Karttunen and Peters, 1979): 
(5) Even Bill likes Mary. 
(6) 1. Bill likes Mary. 
2. Other people besides Bill like Mary; and 
of the people under consideration, Bill is 
the least likely to like Mary. 
The precise status of such pragmatic inferences is 
controversial. We take no stand here on this issue, or 
on the definition of "presupposition". We will simply 
say that, for example, (4.1) is due to the asserted 
meaning of only, and that (4.2) is produced by the 
non-asserted meaning of only. 
1.2 Requirements of a semantics for 
focusing subjuncts 
We desire a semantics for focusing subjuncts that 
is compositional (see Section 1.3), computation- 
ally practical, and amenable to a conventional, 
structured, near-first-order knowledge representa- 
tion such as frames. It must cope with the se- 
mantic and syntactic problems of focusing subjuncts 
by being cross-categorial, being sensitive to in- 
tonation, and by distinguishing asserted and non- 
asserted meaning. By cross-categorial semantics we 
mean one that can cope with syntactic variability in 
the arguments of focusing subjuncts. 
We will demonstrate the following: 
• Intonation has an effect on meaning. A focus 
feature is useful to mediate between intona- 
tional information and meaning. 
• It is desirable to capture meaning in a multi- 
part semantic representation. 
• An extended frame-based semantic representa- 
tion can be used in place of higher-order logics 
to capture the meaning of focusing subjuncts. 
1.3 Syntactic and semantic frameworks 
In this paper, we will use a compositionM, frame- 
based approach to semantics. Focusing subjuncts 
have been thought difficult to fit into a composi- 
tional semantics because they change the meaning of 
their matrix sentences in ways that are not straight- 
forward. 
A compositional semantics is characterized by 
the following properties: 
• Each word and well-formed syntactic phrase is 
represented by a distinct semantic object. 
• The semantic representation of a syntactic 
phrase is a systematic function of the represen- 
tation of its constituent words and/or phrases. 
In a compositional semantics, the syntax drives the 
semantics. To each syntactic phrase construction 
rule there corresponds a semantic rule that speci- 
ties how the semantic objects of the constituents are 
(systematically) combined or composed to obtain a 
semantic object for the phrase. Proponents of com- 
positionM semantics argue that natural language it- 
self is for the most part compositional. In addition, 
using a composition semantics in semantic interpre- 
tation has numerous computational advantages. 
The particular incarnation of a compositional se- 
mantics that serves as the semantic framework for 
this work is the frame-based semantic representa- 
tion of Hirst's Absity system (Hirst, 1987, 1988). 
Absity's underlying representation of the world is a 
knowledge base consisting of frames. A frame is 
a collection of stereotypical knowledge about some 
topic or concept (Hirst, 1987, p. 12). A frame is 
usuMly stored as a named structure having associ- 
ated with it a set of slots or roles that may be as- 
signed values or fillers. Absity's semantic objects 
belong to the types in a frame representation lan- 
guage called Frail (Charniak, 1981). Absity uses the 
following types of semantic object: 
• a frame name 
• a slot name 
• a frame determiner 
• a slot-filler pair 
• a frame description (i.e. a frame with zero or 
more slot-filler pairs) 
• eiLher an instance or frame statement (atom or 
frame determiner with frame description) 
A frame determiner is a function that retrieves 
frames or adds them to the knowledge base. A frame 
description describes a frame in the knowledge base. 
The filler of a slot is either an atom, or it is an in- 
stance, specified by a frame statement, of a frame in 
the knowledge base. In order to capture the mean- 
ing of sentences containing focusing subjuncts, we 
will augment Absity's frame-representation language 
with two new semantic objects, to be described in 
Section 3.3. 
The notation Hirst uses for frames is illustrated in 
Figure 1, which is a frame statement translation of 
the sentence 
(7) Ross washed the dog with a new shampoo. 
The semantics we will outline does not depend on 
any particular syntactic framework or theory. How- 
ever, we choose to use Generalized Phrase Structure 
Grammar (GPSG) (Gazdar et al., 1985), because 
this formalism uses a compositional semantics that 
55 
(a ?u (wash ?u (agent=(the 
?x (person ?X (propername--Ross)))) 
(patlent=(the ?y (dog ?y))) (instrument=(a ?z (shampoo ?z (age=new)))) 
)) 
Figure 1: An Absity frame statement 
resembles Montague grammar (Montague, 1973). A 
central notion of GPSG that we will make use of is 
that of the features of a syntactic phrase. A feature is 
a piece of linguistic information, such as tense, num- 
ber, and bar level; it may be atom-valued or category- 
valued. 
1.4 Previous research 
The groundwork for the analysis of focusing sub- 
juncts was laid by Horn (1969). ttom describes 
only (when modifying an NP) as a predicate tak- 
ing two arguments, "the term ix\] within its scope" 
and "some proposition \[Pz\] containing that term" 
(Horn, 1969, p. 99). The meaning of the predicate is 
then to presuppose that the proposition P is true of 
z, and to assert that x is the unique term of which P 
is true: -,(~y)(y # z & Py). Even takes the same ar- 
guments. It is said to presuppose (qy)(y # x & Py) 
and to assert Px. Horn requires a different formula- 
tion of the meaning of only when it modifies a VP. 
Since his formulation is flawed, we do not show it 
here. 
Jackendoff's (1972, p. 242) analysis of even and 
only employs a semantic marker F that is assumed to 
be present in surface structure and associated with 
a node containing stress. He calls the semantic ma- 
terial associated with constituents marked by F the 
focus of a sentence. Fie proposes a rule that states 
that even and "related words" are associated with 
focus by having the focus in their range. Differ- 
ences between the ranges of various focusing adverbs 
account for their different distributions (Jackendoff, 
1972, pp. 249-250). For example: 
Range of even: If even is directly dominated by a 
node X, then X and all nodes dominated by X 
are in its range. 
Range of only: If only is directly dominated by a 
node X, then X and all nodes that are both 
dominated by X and to the right of only are in 
its range. 
That is, only cannot precede its focus (nor can just, 
which has the same range), but even can: 
(8) 1. *(JOHN) only gave Mary a birthday 
present (no one else did). 
2. (JOHN) even gave Mary a birthday 
present (and so did everyone else, but 
John was the person least expected to). 
We will employ several aspects of Rooth's (1985) 
domain selection theory. A key feature of the 
theory is that only takes the VP adjacent to it in 
S-structure as its argument (an extension of the the- 
ory allows only to take arguments other than VPs). 
Rooth describes technical reasons for this arrange- 
ment (1985, p. 45). Among these is the fact that 
focusing subjuncts can draw attention to two (or 
more) items that, syntactically, do not together con- 
stitute a well-formed phrase: 
(9) John only introduced (BILL) to (SUE). 
The prevailing linguistic theories allow a node (such 
as a focusing subjunct) only one argument in the 
syntactic or logical (function-argument) structures 
of a sentence. 
According to Rooth, the asserted meaning of 
(10) John only \[vP introduced BILL to Sue\]. 
is "if John has a property of the form 'introduce y to 
Sue' then it is the property 'introduce Bill to Sue'" 
(Rooth, 1985, p. 44, p. 59). Rooth's theory would 
produce the same translation, shown in (11.2), for 
both sentence (10) and sentence (11.1). 
(11) 1. John only introduced Bill to SUE. 
2. VP\[\[P(john) & P 6 C\] 
--* P = ^introduee'(bill, sue)\] 
P ranges over propositions, so (11.2) is a quantifica- 
tion over propositions. C is bound 2 to the p-set of 
the VP of whichever sentence's meaning (11.2) is in- 
tended to capture. This p-set is "a set of properties, 
which we think of as the set of relevant properties" 
(Rooth, 1985, p. 43). 
Different truth conditions for the two sentences 
(10) and (11.1) obtain because their VPs have dif- 
ferent p-sets: the computation of p-sets is sensitive 
to intonational stress (actually to focus, which is sig- 
nalled by stress; see below). The desired value for C 
in the translation of (10) is the set of propositions of 
the form "introduce y to Sue", namely propositions 
satisfying (12.1). For the translation of (11.1), C is 
the set of propositions of the form "introduce Bill to 
y", that is, those satisfying (12.2). 
(12) 1. AP3y\[P = ^introdued(y, sue)\] 
2. AP3y\[P = ^introduee'(bill, y)\] 
These result in the final translations (13.1) and 
(13.2) respectively for sentences (10) and (11.1): 
(13) 1. Vy\[introducd(john, y, sue) --+ y=bilO 
2. Vy\[introduce' (john, bill, y) --+ y=sue\] 
2 The mechanism of this binding relies on the translation being 
a formula of which (11.2) is a reasonable simplification; see 
(Rooth, 1985, p. 59). 
56 
The formula (13.1) corresponds to the gloss of the 
meaning of (10) given above. (13.2) is to be inter- 
preted as meaning: "if John has a property of the 
form 'introduce Bill to y' then it is the property 'in- 
troduce Bill to Sue'". 
The p-set of a complete sentence is a set of "rel- 
evant propositions". Rooth defines it recursively, 
from the p-sets of its constituents (Rooth, 1985, 
p. 14) (the "model" is a Montague-style formal 
model): 
(14) Let a be a constituent with translation a ~. The 
p-set of a is: 
1. if a bears the focus feature, the set of ob- 
jects in the model matching a ~ in type; 
2. if a is a non-focused non-complex phrase, 
the unit set {a'}; 
3. if a is a non-focused complex phrase, 
the set of objects that can be obtained 
by picking one element from each of the 
p-sets corresponding to the component 
phrases of a, and applying the semantic 
rule for a to this sequence of elements. 
In other words, the p-set of a sentence consists essen- 
tially of all propositions that are "like" the propo- 
sition that it asserts, except that the focused con- 
stituent in the proposition is replaced by a variable. 3 
We will adopt Rooth's definition of the meaning 
of only: A sentence containing only that (without 
only) has logical form a: 
(15) 1. asserts that any "contextually relevant" 
proposition P whose extension is true is 
the proposition a; 
2. has a as part of its non.asserted meaning. 
(Rooth, 1985, p. 120). 
Our analogous definition of even is this: A sentence 
containing even that (without even) has logical form 
a: 
(16) 1. asserts a; 
2. conveys the non-asserted inference that 
there are other "contextually relevant" 
propositions, besides a, that are true. 
2 Devices used to solve the problems 
Our semantics (which is described in more detail by 
Lyons (1989)) employs devices described in the fol- 
lowing sections. 
2.1 The focus feature 
Following Jackendoff, we propose that focus is a bi- 
nary feature, similar to (say) gender and number, 
aThe notion that the meaning of only and even can be defined 
in terms of a base form (such as "John introduced y to Sue") 
was also noted by Kaxttunen and Peters (1979) and McCord 
(1982). 
that is either present or absent on every constituent 
at surface structure. 4 Focus is initially instantiated 
onto the leaves of the tree that represent intona- 
tionally stressed words. The only realization of the 
focus feature that we accommodate is intonational 
accent; however, our theory can easily be extended 
to allow for other overt realizations of focus, includ- 
ing other intonational effects (e.g. (Hirschberg and 
Pierrehumbert, 1986)). Focus is optionally and non- 
deterministically percolated up the syntax tree, to 
any node from its rightmost daughter (rightmost be- 
cause stress manifests itself only at the end of the 
focused constituent (Anderson, 1972)). The non- 
determinism of the percolation of focus is responsible 
for ambiguity in the interpretation of sentences with 
focusing subjuncts. How far the focus feature per- 
colates up determines how wide a focus is attributed 
to the focusing subjunct: 
(17) 1. John also read the book (from the LIBRARY) (as 
well as the one from the 
store). 
2. John also read (the book from the LIBRARY) (as 
well as the newspaper). 
3. John also Iread the book from the LIBRARY) (as 
well as completing his as- 
signment). 
The ambiguous interpretations of a sentence with a 
focusing subjunct belong to an ordered set in which 
each reading has a wider focus for the focusing sub- 
junct than the previous one. 
2.2 Relevant propositions 
Our semantics employs a computational analogue of 
Rooth's p-sets for a frame representation. Our p- 
set for a constituent is computed compositionally, 
along with the semantic representation, in tandem 
with the application of the syntactic rule used to 
build the constituent. The p-set turns out to be an 
object in the frame representation that is like the 
semantic assertion derived for the constituent, but 
lacking restrictive information associated with any 
focused components. 
2.3 Two-part semantics 
In addition to p-sets, two semantic expressions are 
computed for each constituent during the interpre- 
tation of a sentence. One expression represents as- 
serted meaning, and the other, non-asserted mean- 
ing. 
4 This feature is what Jackendoffcalls the F marker, but is dif- 
ferent from what he calls "focus". Note that we use the term 
focus of a focusing subjunct to stand for a distinct con- 
cept: the item to which a focusing subjunct draws attention 
to, or focuses. This is the semantic material that corresponds 
to a stressed word or to a constituent containing one. 
57 
2.4 Linguistic features 
Focus is marked as a binary feature on all syntactic 
constituents. The semantic rules use this informa- 
tion when constructing semantic expressions for con- 
stituents. Because the focus feature need not perco- 
late all the way up to the level of the constituent 
that is adjacent to the focusing subjunct in the syn- 
tax tree, we have found it useful to employ a second 
feature, focus.in, that indicates whether or not any 
sub-phrase is focused. The restriction that a focus- 
ing subjunct adjoins only to a phrase containing fo- 
cus is implemented by requiring the adjunct phrase 
to be (focus-in +). 
Range (see Section 1.4) is implemented as two bi- 
nary features, range-right and range-left, that indi- 
cate whether or not a given focusing subjunct can 
adjoin to phrases to its right and left, respectively. 
(Some words, like even, have both features.) 
2.5 Sentential operators 
Rooth applies his even and only operators to the logi- 
cal form of the constituent that is the syntactic sister 
of the focusing subjunct. So, for example, in the VP 
(18.1), only transforms the expression wash'(dog), 
which is the translation of the VP argument of only, 
into the A-expression (18.2). 
(18) 1. only \[vp washed the (DOG)\] 
2. AxVP\[\[VP & P e C'\] 
P = ^wash'(x, dog)\] 
For each focusing subjunct, Rooth must define a sep- 
arate transformation for each different semantic type 
of phrase that it may take as an argument. He de- 
fines a basic sentential operator for each focusing 
subjunct, and then derives the other operators from 
these (Rooth, 1985, pp. 120-121). 
Our approach is to instead define a single operator 
for each focusing subjunct, essentially Rooth's basic 
sentential operator. This operator takes the seman- 
tic representation of a sentence as an argument and 
produces another semantic representation of senten- 
tial type. When sentential objects are not available, 
as in the interpretation of \[vp only VP\], we delay the 
application of the operator until such a point as fully 
developed propositions, the semantic objects of sen- 
tenees, are available. To do this, the grammar rules 
"percolate" focusing subjunct operators up the syn- 
tax tree to the S node. Our grammar employs the 
feature fs to carry this latent operator. When the 
interpretation of a sentence is otherwise completed, 
a final step is to apply any latent operators, produc- 
ing expressions for the sentence's asserted and non- 
asserted meanings from expressions for its assertion 
and its p-set. 
Several pieces of evidence motivate this approach: 
• As Rooth observed, in order to define a family of 
cross-categorial operators for (say) only, a basic 
operator must be defined that operates on an 
expression of sentential type. The semantics of 
focusing subjuncts actually seems to take place 
at the sentence level. 
Focusing subjuncts normally occur at most once 
per sentence. Even granting the acceptability of 
sentences containing several focusing subjuncts, 
such sentences are clearly semantically compli- 
cated. 
The principal advantage of our approach is that 
it constructs essentially the same final translation 
of a sentence as Rooth's, but avoids using the A- 
operator during the derivation of a semantic repre- 
sentation that does not itself contain a A-operator. 
This is desirable, as A-expressions would make the 
frame representation language less tractable. 
3 Details of the semantics 
3.1 Semantic features 
Three semantic objects are computed for and at- 
tached to each syntactic constituent, in parallel with 
the syntactic processing. The objects are of the 
types defined in an Absity-like frame representation. 
They are attached to a node as values of the fol- 
lowing features (an approach motivated by Shieber 
(1986)): 
Assert: The asserted meaning of the constituent, its 
contribution to the sentence's asserted mean- 
ing. The value is computed the same way 
that a Montague-style grammar would con- 
struct a constituent's logical form from those 
of its daughters. Figure 2 shows examples of 
the rules to compute this value. 
Presupp: The constituent's contribution to the sen- 
tence's non-asserted meaning. For all rules but 
sentence rules, the presupp feature on the parent 
node is undefined. In order not to commit our- 
selves to the status of the non-asserted mean- 
ings of focusing subjuncts, we reserve this fea- 
ture for the non-asserted meanings introduced 
by focusing subjunct operators (see below). 
P-set: A prototype of the semantic objects in the 
node's p-set. All objects that match this object 
are in the node's p-set. The algorithm for com- 
puting p-sets distinguishes between two cases: 
Case 1: If the parent node X (being con- 
structed) is (focus +), its p-set is a variable 
of the same type as the assert object. 
Case 2: Otherwise, the p-set of X is con- 
structed from the p-set values of the con- 
stituent phrases in a manner exactly paral- 
leling the construction of the assert feature. 
58 
Syntax rule Semantic rule 
S --* XP\[(assert (agent = a))\], S = S\[(assert (frame ~ (agent = 4) sf-pairs))\] 
VP\[(assert (frame fl sf-pairs))\] 
VP ---* V\[2 (assert (frame ?t~))\], VP = V\[(assert (frame ?a (slotfl = ~)))1 
NP\[obj (assert (slot~ = ¢))\] 
PP --* P\[38 (assert slota)\], PP = PP\[(assert (slots = fl))l 
NP\[(assert fi)\] 
Figure 2: Examples of semantic rules for the assert feature 
3.2 Application of the focusing subjunct 
operators 
There is a syntactic rule whose sole purpose is to 
support of the application of a sentential operator: 
09) s H\[(fs 4)1 
S\[fs 4\] is specified as a non-initial category in the 
grammar, if a ¢ "-". Therefore, the rule (19) must 
apply in the derivation of any well-formed sentence 
containing a focusing subjunct. The corresponding 
semantic rule (20) applies a focusing subjunct oper- 
ator to the semantic representation of the sentence. 
(20) 1. Input: 
S\[(assert a), (p-set ~/), (fs 7)\] 
2. Output: 
• If 7 = "-" then 
S\[(assert a), (p-set fl)\] 
• else 
S\[(assert oplv(t~ , fi)), 
(presupp op2,(tr, fl)), 
(p-set fl)\] 
where oplv and op2v are the sentential operators for 
the focusing subjunct 7 (see below). 
3.3 The sentential operators 
The sentential operators for only and even are given 
below. (The one for too is the same as that for even, 
and those for the other focusing subjuncts are simi- 
lar.) 
(21) 1. oplontu(A, P) = if P then A 
2. op2only (A, P) = A 
3. opl~,e,(A, P) = A 
4. op2~ven( (the ?x frame-descrA), 
(the ?y frame-descrP) ) 
= (anew ?y ¢?z (frame-descrP)) 
The form if P then A is a directive to the underly- 
ing knowledge base to insert the rule that any frame 
matching P is just the frame A, that is, A is the 
unique frame matching P. This directive is a frame 
implication. It is similar in character to a frame 
determiner (Hirst, 1987), in that it is a function that 
manipulates the underlying knowledge base. 
The form (anew ?y ~?X frame-descrP) is also a 
new type of entity in the semantics. We treat it as a 
frame determiner. It is a directive to the knowledge 
base to retrieve or create a frame instance, ?y, that 
matches frame-descrP but is not the frame instance 
identified by the variable ?x. As with the frame 
determiner (the ?x), such a frame instance ?y should 
be inserted if not already present in the knowledge 
base. 
For example, the sentence (22.1) yields the ex- 
pression (22.2) as its assertion and (22.3) as its 
non-asserted meaning (other readings are possible 
as well). 
(22) 1. Ross only washed the DOG. 
2. if (wash ?x (agent=Ross)) then 
(wash ?x (agent=Ross) (patient=dog))) 
3. (the ?x (wash ?x (agent=Ross) 
(patient=dog))) 
The frame instance (22.3) captures the semantic con- 
tent of the sentence "Ross washed the dog". The 
frame implication (22.3) is to be interpreted as the 
rule that any wash frame in the knowledge base hav- 
ing Ross as its agent must in addition have dog as 
its patient. 
A second example: sentence (23.1) yields assertion 
(23.2) and non-asserted meaning (23.3). 
(23) 1. Ross washed even the DOG. 
2. (the ?x (wash ?x 
(agent=Ross) (patient=dog))) 
3. (anew ?y ~?x (wash ?y (agent=Ross))) 
The expression (23.3) affirms the existence of a wash 
instance ?y having agent Ross but that is a distinct 
washing from ?z in (23.2), which has dog as its pa- 
tient. 
4 The implementation 
IDEO (Interpreter Designed for Even and Only) is 
a limited semantic interpreter that incorporates the 
59 
semantics for even and only described in Section 3. 
The implementation is in Edinburgh C-Prolog, run- 
ning under UNIX on a Sun-4 computer. Because the 
authors did not have access to a working version 
of Frail (see Section 1.3), IDEO runs on top of a 
toy knowledge base, also implemented in C-Prolog, 
whose retrieval language is (unfortunately) a syntac- 
tic variant of Absity's. 
A sample session with IDEO is follows below. In 
this trace, output generated by the program or typed 
by the user is shown in typewriter font. As the ex- 
ample shows, IDEO accepts a sentence typed at the 
keyboard and outputs four different things. Firstly, 
it echoes the sentence in its internal Prolog format. 
Secondly, the GPSG category obtained for the sen- 
tence, which incorporates a parse tree for the sen- 
tence, is displayed. For the sake of readability, IDEO 
prints a simplified version of the category. Then, it 
prints separately the semantic representation of the 
sentence, which consists of several of the feature- 
value pairs of the sentence category. Lastly, it dis- 
plays a message about the success or failure of each 
knowledge base function call resulting from process- 
ing the semantic representation of the sentence. In 
a question-and-answer system, these messages would 
be replaced by generated English answers. 
Please enter a sentence, follo.ed by a 
carriage return, after the "I:" prompt. 
J: Ross only washed the :dog. 
The colon preceding the word dog tells IDEO that 
the word isintonationally stressed. 
>>> Sa~ the sentence: 
\[ross. only. ,ashed. the. stress(dog). 
period\] 
>>> The category for this sentence is: 
\[Omitted due to space ~mitations.\] 
The significant piece of information in the 
GPSG category is that the noun phrase \[NP the 
stress(dog)\] is (focus +), but the verb phrase that 
contains it is not. 
>>> The semantic representation is: 
assert( 
if frame(X, .ash) k slot(X, agent, ross) 
then frame(X, .ash) 
k slot(X, agent, ross) 
slot(X, patient, Y) 
k framedet(the. Y, frame(Y, dog))) 
presupp(framedet(a, X, 
frame(X..ash) k slot(X, agent, ross) 
k slot(X, patient. Y) 
k framedet(the, Y, frame(Y, dog)))) 
p-set(framedet(a. X, 
frame(X, .ash) k slot(X, agent, ross))) 
fs(only) 
>>> OK? no 
This semantic representation corresponds to the 
reading in which the speaker means to assert that 
Ross washed nothing else but the dog. The user 
replies no to the prompt OK? to indicate that this is 
not the reading he intends. 
>>> The category for this sentence is: 
\[Omitted due to space limitations.\] 
This time, a parse is returned in which the feature 
(focus +) percolates up the parse tree to the entire 
verb phrase \[NP .ashed the stress(dog)\], 
>>> The semantic representation is: 
assert( 
if slot(X, agent, ross) 
then frame(X, .ash) 
k slot(X, agent, ross) 
k slot(X, patient, Y) 
k framedet(the, Y, frame(Y, dog))) 
presupp(framedet(a, X. 
frame(X, .ash) k slot(X, agent, ross) 
slot(X, patient, Y) 
k framedet(the, Y, frame(Y, dog)))) 
p-set(framedet(a, X. 
slot(X, agent, ross))) 
fs(only) 
>>> OK? yes 
The user approves this semantic representation, 
which corresponds to the reading in which the 
speaker asserts that Ross did nothing but wash the 
dog. 
>>> Retrieved frame "dogl" 
frame (dog1. dog) 
>>> Found frame "washl" 
frame (wash1, .ash) 
slot(.ashl, agent, ross) 
slot(.ashl, patient, dogl) 
>>> Inserted rule "rulel" 
if 
slot(X, agent, ross) 
then 
X = .ashl 
The knowledge base now is constrained by the rule 
rulel. This says that ira frame X satisfies the frame 
description slot(X, agent, ross)(i.e, its agent is 
ross), then it must be the frame ,ashl (a ,ash 
frame whose patient slot is filled by dogl). 
60 
5 Conclusions 
This paper summarizes work, details of which can be 
found in (Lyons, 1989). The work represents a step 
towards better understanding of focusing subjuncts 
and of compositional semantics in general. The se- 
mantics we have proposed allows focusing subjuncts 
to be covered by a frame-based approach to semantic 
interpretation, by virtue of its being compositional, 
computationally practical, able to differentiate be- 
tween asserted and non-asserted meaning, sensitive 
to intonation, and eross-categorial. We have found 
that: 
• Focus and stress information can be used to ad- 
vantage in a semantic interpreter. 
• The hypothesis that focus may be optionally 
percolated to a parent node from a daughter 
explains the scope ambiguities observed in the 
interpretation of focusing subjuncts. 
• Rooth's method of obtaining the translation of 
a focusing subjunct by using p-sets to select 
"domains of quantification" can be adapted to 
translating a sentence into a frame represents- 
tion. 
• Treating focusing subjuncts as operators on sen- 
tential semantic forms makes this translation 
possible. 
• Semantically, focusing subjuncts are not just 
passive objects for composition. We have shown 
extensions to standard frame representations 
that are required for the translation of focus- 
ing subjuncts. 
Acknowledgements 
Both authors acknowledge the support of the Natural 
Sciences and Engineering Research Council of Canada. 
We are also grateful to Diane Horton, Brendan Gillon, 
Barb Brunson, and Mark Hyan for discussions, com- 
ments on earlier drafts, and general encouragement. 
References 
Anderson, Stephen R. (1972). How to get even. Lan. 
guage, 48:893-906. 
Charniak, Eugene (1981). A common representation for 
problem-solving and language-comprehension infor- 
mation. Artificial Intelligence, 16(3):225-255. Also 
published as technical report CS-59, Department of 
Computer Science, Brown University, July 1980. 
Gazdar, Gerald, Klein, Ewan, Pullum, Geoffrey K., and 
Sag, Ivan (1985). Generalized Phrase Structure 
Grammar. Harvard University Press. 
Hirschberg, Julia and Pierrehumbert, Janet (1986). The 
intonational structuring of discourse. In 24 th An- 
nual Meeting of the Association for Computational 
Linguistics, Proceedings of the Conference. pages 
136-143. 
Hirst, Graeme (1987). Semantic Interpretation and the 
Resolution of Ambiguity. Cambridge University 
Pre88. 
Hirst, Graeme (1988). Semantic interpretation and am- 
biguity. Artificial Intelligence, 34(2):131-177. 
Horn, Laurence R. (1969). A presuppositional analy- 
sis of only and even. In Binnick, Robert I., Davi- 
son, Alice, Green, Georgia, and Morgan, Jerry, edi- 
tors, Papers from the Fifth Regional Meeting of the 
Chicago Linguistics Society. Chicago Linguistic So- 
ciety, pages 98-107. 
Jackendoff, Ray S. (1972). Semantic Interpretation in 
Generative Grammar. The MIT Press. 
Karttunen, Lanri and Peters, Stanley (1979). Conven- 
tional implicature. In Oh, Choon-Kyu and Din- 
neen, David A., editors, Presupposition, volume 11 
of Syntaz and Semantics. Academic Press, pages 1- 
56. 
Lyons, Dan (1989). A computational semantics for fo- 
cusing subjuncts. Master's thesis, Department of 
Computer Science, University of Toronto. Also 
published as technical report CSRI-234. 
McCord, Michael C. (1982). Using slots and modifiers 
in logic grammars for natural language. Artificial 
Intelligence, 18:327-367. 
Montague, Richard (1973). The proper treatment 
of quantification in ordinary English. In Hin- 
tiklm, Kaarlo Jaakko Juhani, Moravcsik, Julius 
Matthew Emil, and Suppes, Patrick Colonel, edi- 
tors, Approaches to Natural Language: Proceedings 
of the 1970 Stanford workshop on grammar and se- 
mantics. D. Reidel, pages 221-242. Also in Thoma~ 
son, Richmond Hunt (ed.), Formal philosophy: Se- 
lected papers of Richard Montague. Yale University 
Press (1974): 247-270. 
Quirk, Randolph, Greenbaum, Sidney, Leech, Geoffrey, 
and Svartvik, Jan (1965). A Comprehensive Gram- 
mar of the English Language. Longman. 
Rooth, Mats Edward (1985). Association with Focus. 
PhD thesis, Department of Linguistics, University 
of Massachusets. 
Shieber, Stuart M. (1986). An Introduction to 
Unification-Based Approaches to Grammar. Cen- 
ter for the Study of Language and Information. 
61 
