The Generative Lexicon 
James Pustejovsky" 
Computer Science Department 
Brandeis University 
In this paper, I will discuss four major topics relating to current research in lexical seman- 
tics: methodology, descriptive coverage, adequacy of the representation, and the computational 
usefulness of representations. In addressing these issues, I will discuss what I think are some 
of the central problems facing the lexical semantics community, and suggest ways of best ap- 
proaching these issues. Then, I will provide a method for the decomposition of lexical categories 
and outline a theory of lexical semantics embodying a notion of cocompositionality and type 
coercion, as well as several levels of semantic description, where the semantic load is spread 
more evenly throughout the lexicon. I argue that lexical decomposition is possible if it is per- 
formed generatively. Rather than assuming a fixed set of primitives, I will assume a fixed 
number of generative devices that can be seen as constructing semantic expressions. I develop 
a theory of Qualia Structure, a representation language for lexical items, which renders much 
lexical ambiguity in the lexicon unnecessary, while still explaining the systematic polysemy 
that words carry. Finally, I discuss how individual lexical structures can be integrated into the 
larger lexical knowledge base through a theory of lexical inheritance. This provides us with 
the necessary principles of global organization for the lexicon, enabling us to fully integrate 
our natural language lexicon into a conceptual whole. 
1. Introduction 
I believe we have reached an interesting turning point in research, where linguistic 
studies can be informed by computational tools for lexicology as well as an appre- 
ciation of the computational complexity of large lexical databases. Likewise, com- 
putational research can profit from an awareness of the grammatical and syntactic 
distinctions of lexical items; natural language processing systems must account for 
these differences in their lexicons and grammars. The wedding of these disciplines is 
so important, in fact, that I believe it will soon be difficult to carry out serious com- 
putational research in the fields of linguistics and NLP without the help of electronic 
dictionaries and computational lexicographic resources (cf. Walker et al. \[forthcoming\] 
and Boguraev and Briscoe \[1988\]). Positioned at the center of this synthesis is the study 
of word meaning, lexical semantics, which is currently witnessing a revival. 
In order to achieve a synthesis of lexical semantics and NLP, I believe that the 
lexical semantics community should address the following questions: 
1. Has recent work in lexical semantics been methodologically sounder 
than the previous work in the field? 
2. Do theories being developed today have broader coverage than the 
earlier descriptive work? 
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Computational Linguistics Volume 17, Number 4 
3. Do current theories provide any new insights into the representation of 
knowledge for the global structure of the lexicon? 
4. Finally, has recent work provided the computational community with 
useful resources for parsing, generation, and translation research? 
Before addressing these questions, I would like to establish two basic assumptions 
that will figure prominently in my suggestions for a lexical semantics framework. 
The first is that, without an appreciation of the syntactic structure of a language, 
the study of lexical semantics is bound to fail. There is no way in which meaning 
can be completely divorced from the structure that carries it. This is an important 
methodological point, since grammatical distinctions are a useful metric in evaluating 
competing semantic theories. 
The second point is that the meanings of words should somehow reflect the deeper, 
conceptual structures in the system and the domain it operates in. This is tantamount 
to stating that the semantics of natural language should be the image of nonlinguistic 
conceptual organizing principles (whatever their structure). 
Computational lexical semantics should be guided by the following principles. 
First, a clear notion of semantic well-formedness will be necessary to characterize a 
theory of possible word meaning. This may entail abstracting the notion of lexical 
meaning away from other semantic influences. For instance, this might suggest that 
discourse and pragmatic factors should be handled differently or separately from the 
semantic contributions of lexical items in composition. 1 Although this is not a necessary 
assumption and may in fact be wrong, it may help narrow our focus on what is 
important for lexical semantic descriptions. 
Secondly, lexical semantics must look for representations that are richer than the- 
matic role descriptions (Gruber 1965; Fillmore 1968). As argued in Levin and Rap- 
paport (1986), named roles are useful at best for establishing fairly general mapping 
strategies to the syntactic structures in language. The distinctions possible with theta- 
roles are much too coarse-grained to provide a useful semantic interpretation of a 
sentence. What is needed, I will argue, is a principled method of lexical decomposi- 
tion. This presupposes, if it is to work at all, (1) a rich, recursive theory of semantic 
composition, (2) the notion of semantic well-formedness mentioned above, and (3) an 
appeal to several levels of interpretation in the semantics (Scha 1983). 
Thirdly, and related to the point above, the lexicon is not just verbs. Recent work 
has done much to clarify the nature of verb classes and the syntactic constructions 
that each allows (Levin 1985, 1989). Yet it is not clear whether we are any closer to 
understanding the underlying nature of verb meaning, why the classes develop as 
they do, and what consequences these distinctions have for the rest of the lexicon 
and grammar. The curious thing is that there has been little attention paid to the other 
lexical categories (but see Miller and Johnson-Laird \[1976\], Miller and Fellbaum \[1991\], 
and Fass \[1988\]). That is, we have little insight into the semantic nature of adjectival 
predication, and even less into the semantics of nominals. Not until all major categories 
have been studied can we hope to arrive at a balanced understanding of the lexicon 
and the methods of composition. 
Stepping back from the lexicon for a moment, let me say briefly what I think the 
1 This is still a contentious point and is an issue that is not at all resolved in the community. Hobbs 
(1987) and Wilensky (1990), for example, argue that there should be no distinction between commonsense knowledge and lexical knowledge. Nevertheless, I will suggest below that there are 
good reasons, both methodological and empirical, for establishing just such a division. Pustejovsky and Bergler (1991) contains a good survey on how this issue is addressed by the community. 
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James Pustejovsky The Generative Lexicon 
position of lexical research should be within the larger semantic picture. Ever since 
the earliest attempts at real text understanding, a major problem has been that of con- 
trolling the inferences associated with the interpretation process. In other words, how 
deep or shallow is the understanding of a text? What is the unit of well-formedness 
when doing natural language understanding; the sentence, utterance, paragraph, or 
discourse? There is no easy answer to this question because, except for the sentence, 
these terms are not even formalizable in a way that most researchers would agree on. 
It is my opinion that the representation of the context of an utterance should be 
viewed as involving many different generative factors that account for the way that 
language users create and manipulate the context under constraints, in order to be 
understood. Within such a theory, where many separate semantic levels (e.g. lexical 
semantics, compositional semantics, discourse structure, temporal structure) have in- 
dependent interpretations, the global interpretation of a "discourse" is a highly flexible 
and malleable structure that has no single interpretation. The individual sources of se- 
mantic knowledge compute local inferences with a high degree of certainty (cf. Hobbs 
et al. 1988; Charniak and Goldman 1988). When integrated together, these inferences 
must be globally coherent, a state that is accomplished by processes of cooperation 
among separate semantic modules. The basic result of such a view is that semantic 
interpretation proceeds in a principled fashion, always aware of what the source of a 
particular inference is, and what the certainty of its value is. Such an approach allows 
the reasoning process to be both tractable and computationally efficient. The repre- 
sentation of lexical semantics, therefore, should be seen as just one of many levels in 
a richer characterization of contextual structure. 
2. Methods in Lexical Semantics 
Given what I have said, let us examine the questions presented above in more detail. 
First, let us turn to the issue of methodology. How can we determine the soundness 
of our method? Are new techniques available now that have not been adequately 
explored? Very briefly, one can summarize the most essential techniques assumed by 
the field, in some way, as follows (see, for example Cruse \[1986\]): 
• On the basis of categorial distinctions, establish the fundamental 
differences between the grammatical classes; the typical semantic 
behavior of a word of category X. For example, verbs typically behave as 
predicators, nouns as arguments. 
• Find distinctions between elements of the same word class on the basis 
of collocation and cooccurrence tests. For example, the nouns dog and 
book partition into different selectional classes because of contexts 
involving animacy, while the nouns book and literature partition into 
different selectional classes because of a mass/count distinction. 
• Test for distinctions of a grammatical nature on the basis of diathesis; i.e. 
alternations that are realized in the syntax. For example, break vs. cut in 
(1) and (2) below (Fillmore 1968; Lakoff 1970; Hale and Keyser 1986): 
Example 1 
a. The glass broke. 
b. John broke the glass. 
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Example 2 
a. *The bread cut. 
b. John cut the bread. 
Such alternations reveal subtle distinctions in the semantic and syntactic 
behavior of such verbs. The lexical semantic representations of these 
verbs are distinguishable on the basis of such tests. 
Test for entailments in the word senses of a lexical item, in different 
grammatical contexts. One can distinguish, for example, between 
context-free and context-sensitive entailments. When the use of a word 
always entails a certain proposition, we say that the resulting entailment 
is not dependent on the syntactic context (cf. Katz and Fodor 1963; 
Karttunen 1971, 1974; Seuren 1985). This is illustrated in Example 3, 
where a killing always entails a dying. 
Example 3 
a. John killed Bill. 
b. Bill died. 
When the same lexical item may carry different entailments in different 
contexts, we say that the entailments are sensitive to the syntactic 
contexts; for example, forget in Example 4, 
Example 4 
a. John forgot that he locked the door. 
b. John forgot to lock the door. 
Example 4a has a factive interpretation of forget that 4b does not carry: in 
fact, 4b is counterfactive. Other cases of contextual specification involve 
aspectual verbs such as begin and finish as shown in Example 5. 
Example 5 
a. Mary finished the cigarette. 
b. Mary finished her beer. 
The exact meaning of the verb finish varies depending on the object it 
selects, assuming for these examples the meanings finish smoking or finish 
drinking. 
Test for the ambiguity of a word. Distinguish between homonymy and 
polysemy, (cf. Hirst 1987; Wilks 1975b); that is, from the accidental and 
logical aspects of ambiguity. For example, the homonymy between the 
two senses of bank in Example 6 is accidental. 2 
Example 6 
a. the bank of the river 
b. the richest bank in the city 
2 Cf. Weinreich (1972) distinguishes between contrastive and complementary polysemy, essentially 
covering this same distinction. See Section 4 for discussion. 
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James Pustejovsky The Generative Lexicon 
In contrast, the senses in Example 7 exhibit a polysemy (cf. Weinreich 
1972; Lakoff 1987). 
Example 7 
a. The bank raised its interest rates yesterday (i.e. the institution). 
b. The store is next to the new bank (i.e. the building). 
• Establish what the compositional nature of a lexical item is when applied 
to other words. For example, alleged vs. female in Example 8. 
Example 8 
a. the alleged suspect 
b. the female suspect 
While female behaves as a simple intersective modifier in 8b, certain 
modifiers such as alleged in 8a cannot be treated as simple attributes; 
rather, they create an intensional context for the head they modify. An 
even more difficult problem for compositionality arises from phrases 
containing frequency adjectives (cf. Stump 1981), as shown in 8c and 8d. 
Example 8 
c. An occasional sailor walks by on the weekend. 
d. Caution: may contain an occasional pit (notice on a box of prunes). 
The challenge here is that the adjective doesn't modify the nominal head, 
but the entire proposition containing it (cf. Partee \[1985\] for discussion). 
A similar difficulty arises with the interpretation of scalar predicates 
such as fast in Example 9. Both the scale and the relative interpretation 
being selected for depends on the noun that the predicate is modifying. 
Example 9 
a. a fast typist: one who types quickly 
b. a fast car: one which can move quickly 
c. a fast waltz: one with a fast tempo 
Such data raise serious questions about the principles of compositionality 
and how ambiguity should be accounted for by a theory of semantics. 
This just briefly characterizes some of the techniques that have been useful for 
arriving at pre-theoretic notions of word meaning. What has changed over the years 
are not so much the methods themselves as the descriptive details provided by each 
test. One thing that has changed, however -- and this is significant -- is the way 
computational lexicography has provided stronger techniques and even new tools for 
lexical semantics research: see Atkins (1987) for sense discrimination tasks; Amsler 
(1985), Atkins et al. (forthcoming) for constructing concept taxonomies; Wilks et al. 
(1988) for establishing semantic relatedness among word senses; and Boguraev and 
Pustejovsky (forthcoming) for testing new ideas about semantic representations. 
3. Descriptive Adequacy of Existing Representations 
Turning now to the question of how current theories compare with the coverage of 
lexical semantic data, there are two generalizations that should be made. First, the 
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taxonomic descriptions that have recently been made of verb classes are far superior 
to the classifications available twenty years ago (see Levin \[1985\] for review). Using 
mainly the descriptive vocabulary of Talmy (1975, 1985) and Jackendoff (1983), fine and 
subtle distinctions are drawn that were not captured in the earlier, primitives-based 
approach of Schank (1972, 1975) or the frame semantics of Fillmore (1968). 
As an example of the verb classifications developed by various researchers (and 
compiled by the MIT Lexicon Project; see Levin \[1985, 1989\]), consider the grammatical 
alternations in the example sentences below (cf. Dow .ty 1991). 
Example 10 
a. John met Mary. 
b. John and Mary met. 
Example 11 
a. A car ran into a truck. 
b. A car and a truck ran into each other. 
Example 12 
a. A car ran into a tree. 
b. *A car and a tree ran into each other. 
These three pairs show how the semantics of transitive motion verbs (e.g. run into) 
is similar in some respects to reciprocal verbs such as meet. The important difference, 
however, is that the reciprocal interpretation requires that both subject and object be 
animate or moving; hence 12b is ill-formed. (cf. Levin 1989; Dowty 1991). 
Another example of how diathesis reveals the underlying semantic differences 
between verbs is illustrated in Examples 13 and 14 below. A construction called the 
conative (see Hale and Keyser \[1986\] and Levin \[1985\]) involves adding the preposition 
at to the verb, changing the verb meaning to an action directed toward an object. 
Example 13 
a. Mary cut the bread. 
b. Mary cut at the bread. 
Example 14 
a. Mary broke the bread. 
b. *Mary broke at the bread. 
What these data indicate is that the conative is possible only with verbs of a particular 
semantic class; namely, verbs that specify the manner of an action that results in a change 
of state of an object. 
As useful and informative as the research on verb classification is, there is a major 
shortcoming with this approach. Unlike the theories of Katz and Fodor (1963), Wilks 
(1975a), and Quillian (1968), there is no general coherent view on what the entire lexi- 
con will look like when semantic structures for other major categories are studied. This 
can be essential for establishing a globally coherent theory of semantic representation. 
On the other hand, the semantic distinctions captured by these older theories were 
often too coarse-grained. It is clear, therefore, that the classifications made by Levin 
and her colleagues are an important starting point for a serious theory of knowledge 
representation. I claim that lexical semantics must build upon this research toward 
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James Pustejovsky The Generative Lexicon 
constructing a theory of word meaning that is integrated into a linguistic theory, as 
well as interpreted in a real knowledge representation system. 
4. Explanatory Adequacy of Existing Representations 
In this section I turn to the question of whether current theories have changed the 
way we look at representation and lexicon design. The question here is whether the 
representations assumed by current theories are adequate to account for the richness 
of natural language semantics. It should be pointed out here that a theory of lexical 
meaning will affect the general design of our semantic theory in several ways. If 
we view the goal of a semantic theory as being able to recursively assign meanings 
to expressions, accounting for phenomena such as synonymy, antonymy, polysemy, 
metonymy, etc., then our view of compositionality depends ultimately on what the 
basic lexical categories of the language denote. Conventional wisdom on this point 
paints a picture of words behaving as either active functors or passive arguments 
(Montague 1974). But we will see that if we change the way in which categories can 
denote, then the form of compositionality itself changes. Therefore, if done correctly, 
lexical semantics can be a means to reevaluate the very nature of semantic composition 
in language. 
In what ways could lexical semantics affect the larger methods of composition in 
semantics? I mentioned above that most of the careful representation work has been 
done on verb classes. In fact, the semantic weight in both lexical and compositional 
terms usually falls on the verb. This has obvious consequences for how to treat lexical 
ambiguity. For example, consider the verb bake in the two sentences below. 
Example 15 
a. John baked the potato. 
b. John baked the cake. 
Atkins, Kegl, and Levin (1988) demonstrate that verbs such as bake are systematically 
ambiguous, with both a change-of-state sense (15a) and a create sense (15b). 
A similar ambiguity exists with verbs that allow the resulative construction, shown 
in Examples 16 and 17, and discussed in Dowty (1979), Jackendoff (1983), and Levin 
and Rapoport (1988). 
Example 16 
a. Mary hammered the metal. 
b. Mary hammered the metal flat. 
Example 17 
a. John wiped the table. 
b. John wiped the table clean. 
On many views, the verbs in Examples 16 and 17 are ambiguous, related by either 
a lexical transformation (Levin and Rapoport 1988), or a meaning postulate (Dowty 
1979). In fact, given strict requirements on the way that a verb can project its lexical 
information, the verb run in Example 18 will also have two lexical entries, depending 
on the syntactic environment it selects (Talmy 1985; Levin and Rappaport 1988). 
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Example 18 
a. Mary ran to the store yesterday. 
b. Mary ran yesterday. 
These two verbs differ in their semantic representations, where run in 18a means go- 
to-by-means-of-running, while in 18b it means simply move-by-running (cf. Jackendoff 
1983). 
The methodology described above for distinguishing word senses is also assumed 
by those working in more formal frameworks. For example, Dowty (1985) proposes 
multiple entries for control and raising verbs, and establishes their semantic equiva- 
lence with the use of meaning postulates. That is, the verbs in Examples 19 and 20 are 
lexically distinct but semantically related by rules. 3 
Example 19 
a. It seems that John likes Mary. 
b. John seems to like Mary. 
Example 20 
a. Mary prefers that she come. 
b. Mary prefers to come. 
Given the conventional notions of function application and composition, there is 
little choice but to treat all of the above cases as polysemous verbs. Yet, something 
about the systematicity of such ambiguity suggests that a more general and simpler 
explanation should be possible. By relaxing the conditions on how the meaning of a 
complex expression is derived from its parts, I will, in fact, propose a very straight- 
forward explanation for these cases of logical polysemy. 
5. A Framework for Computational Semantics 
In this section, I will outline what I think are the basic requirements for a theory of 
computational semantics. I will present a conservative approach to decomposition, 
where lexical items are minimally decomposed into structured forms (or templates) 
rather than sets of features. This will provide us with a generative framework for the 
composition of lexical meanings, thereby defining the well-formedness conditions for 
semantic expressions in a language. 
We can distinguish between two distinct approaches to the study of word mean- 
ing: primitive-based theories and relation-based theories. Those advocating primitives 
assume that word meaning can be exhaustively defined in terms of a fixed set of 
primitive elements (e.g. Wilks 1975a; Katz 1972; Lakoff 1971; Schank 1975). Inferences 
are made through the primitives into which a word is decomposed. In contrast to 
this view, a relation-based theory of word meaning claims that there is no need for 
decomposition into primitives if words (and their concepts) are associated through a 
network of explicitly defined links (e.g. Quillian 1968; Collins and Quillian 1969; Fodor 
1975; Carnap 1956; Brachman 1979). Sometimes referred to as meaning postulates, these 
links establish any inference between words as an explicit part of a network of word 
3 Both Klein and Sag (1985) and Chomsky (1981) assume, however, that there are reasons for relating these two forms structurally. See below and Pustejovsky (1989a) for details. 
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James Pustejovsky The Generative Lexicon 
concepts. 4 What I would like to do is to propose a new way of viewing primitives, 
looking more at the generative or compositional aspects of lexical semantics, rather than 
the decomposition into a specified number of primitives. 
Most approaches to lexical semantics making use of primitives can be character- 
ized as using some form of feature-based semantics, since the meaning of a word is 
essentially decomposable into a set of features (e.g. Katz and Fodor 1963; Katz 1972; 
Wilks 1975; Schank 1975). Even those theories that rely on some internal structure for 
word meaning (e.g. Dowty 1979; Fillmore 1985) do not provide a complete characteri- 
zation for all of the well-formed expressions in the language. Jackendoff (1983) comes 
closest, but falls short of a comprehensive semantics for all categories in language. 
No existing framework, in my view, provides a method for the decomposition of lexical 
categories. 
What exactly would a method for lexical decomposition give us? Instead of a 
taxonomy of the concepts in a language, categorized by sets of features, such a method 
would tell us the minimal semantic configuration of a lexical item. Furthermore, it 
should tell us the compositional properties of a word, just as a grammar informs us 
of the specific syntactic behavior of a certain category. What we are led to, therefore, 
is a generative theory of word meaning, but one very different from the generative 
semantics of the 1970s. 
To explain why I am suggesting that lexical decomposition proceed in a generative 
fashion rather than the traditional exhaustive approach, let me take as a classic example, 
the word closed as used in Example 21 (see Lakoff 1970). 
Example 21 
a. The door is closed. 
b. The door closed. 
c. John closed the door. 
Lakoff (1970), Jackendoff (1972), and others have suggested that the sense in 21c must 
incorporate something like cause-to-become-not-open for its meaning. Similarly, a verb 
such as give specifies a transfer from one person to another, e.g., cause-to-have. Most 
decomposition theories assume a set of primitives and then operate within this set 
to capture the meanings of all the words in the language. These approaches can be 
called exhaustive since they assume that with a fixed number of primitives, complete 
definitions of lexical meaning can be given. In the sentences in 21, for example, close 
is defined in terms of the negation of a primitive, open. Any method assuming a fixed 
number of primitives, however, runs into some well-known problems with being able 
to capture the full expressiveness of natural language. 
These problems are not, however, endemic to all decomposition approaches. I 
would like to suggest that lexical (and conceptual) decomposition is possible if it 
is performed generatively. Rather than assuming a fixed set of primitives, let us as- 
sume a fixed number of generative devices that can be seen as constructing semantic 
expressions. 5 Just as a formal language is described more in terms of the productions 
in the grammar than its accompanying vocabulary, a semantic language is definable 
by the rules generating the structures for expressions rather than the vocabulary of 
primitives itself. 6 
4 For further discussion on the advantages and disadvantages to both approaches, see Jackendoff (1983). 5 See Goodman (1951) and Chomsky (1955) for explanations of the method assumed here. 
6 This approach is also better suited to the way people write systems in computational linguistics. 
Different people have distinct primitives for their own domains, and rather than committing a designer 
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How might this be done? Consider the sentences in. Example 21 again. A minimal 
decomposition on the word closed is that it introduces an opposition of terms: closed 
and not-closed. For the verbal forms in 21b and 21c, both terms in this opposition are 
predicated of different subevents denoted by the sentences. In 21a, this opposition is 
left implicit, since the sentence refers to a single state. Any minimal analysis of the 
semantics of a lexical item can be termed a generative operation, since it operates on the 
predicate(s) already literally provided by the word. This type of analysis is essentially 
Aristotle's principle of opposition (cf. Lloyd 1968), and it will form the basis of one level 
of representation for a lexical item. The essential opposition denoted by a predicate 
forms part of what I will call the qualia structure of that lexical item. Briefly, the qualia 
structure of a word specifies four aspects of its meaning: 
• the relation between it and its constituent parts; 
• that which distinguishes it within a larger domain (its physical 
characteristics); 
• its purpose and function; 
• whatever brings it about. 
I will call these aspects of a word's meaning its Constitutive Role, Formal Role, Telic Role, 
and its Agentive Role, respectively. 7 
This minimal semantic distinction is given expressive force when combined with 
a theory of event types. For example, the predicate in 21a denotes the state of the door 
being closed. No opposition is expressed by this predicate. In 21b and 21c, however, 
the opposition is explicitly part of the meaning of the predicate. Both these predicates 
denote what I will call transitions. The intransitive use of close in 21b makes no mention 
of the causer, yet the transition from not-closed to closed is still entailed. In 21c, the event 
that brings about the closed state of the door is made more explicit by specifying the 
actor involved. These differences constitute what I call the event structure of a lexical 
item. Both the opposition of predicates and the specification of causation are part of a 
verb's semantics, and are structurally associated with slots in the event template for 
the word. As we will see in the next section, there are different inferences associated 
with each event type, as well as different syntactic behaviors (cf. Grimshaw 1990 and 
Pustejovsky 1991). 
Because the lexical semantic representation of a word is not an isolated expression, 
but is in fact linked to the rest of the lexicon, in Section 7, I suggest how the global 
integration of the semantics for a lexical item is achieved by structured inheritance 
through the different qualia associated with a word. I call this the lexical inheritance 
structure for the word. 
Finally, we must realize that part of the meaning of a word is how it translates the 
underlying semantic representations into expressions that are utilized by the syntax. 
This is what many have called the argument structure for a lexical item. I will build on 
Grimshaw's recent proposals (Grimshaw 1990) for how to define the mapping from 
the lexicon to syntax. 
to a particular vocabulary of primitives, a lexical semantics should provide a method for the 
decomposition and composition of lexical items. 
7 Some of these roles are reminiscent of descriptors used by various computational researchers, such as 
Wilks (1975b), Hayes (1979), and Hobbs et al. (1987). Within the theory outlined here, these roles 
determine a minimal semantic description of a word that has both semantic and grammatical 
consequences. 
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James Pustejovsky The Generative Lexicon 
This provides us with an answer to the question of what levels of semantic rep- 
resentation are necessary for a computational lexical semantics. In sum, I will argue 
that lexical meaning can best be captured by assuming the following levels of repre- 
sentation. 
1. Argument Structure: The behavior of a word as a function, with its arity 
specified. This is the predicate argument structure for a word, which 
indicates how it maps to syntactic expressions. 
2. Event Structure: Identification of the particular event type (in the sense 
of Vendler \[1967\]) for a word or phrase: e.g. as state, process, or 
transition. 
3. Qualia Structure: The essential attributes of an object as defined by the 
lexical item. 
4. Inheritance Structure: How the word is globally related to other 
concepts in the lexicon. 
These four structures essentially constitute the different levels of semantic expressive- 
ness and representation that are needed for a computational theory of lexical semantics. 
Each level contributes a different kind of information to the meaning of a word. The 
important difference between this highly configurational approach to lexical semantics 
and feature-based approaches is that the recursive calculus defined for word mean- 
ing here also provides the foundation for a fully compositional semantics for natural 
language and its interpretation into a knowledge representation model. 
5.1 Argument Structure 
A logical starting point for our investigations into the meaning of words is what has 
been called the functional structure or argument structure associated with verbs. What 
originally began as the simple listing of the parameters or arguments associated with 
a predicate has developed into a sophisticated view of the way arguments are mapped 
onto syntactic expressions (for example, the f-structure in Lexical Functional Grammar 
\[Bresnan 1982\] and the Projection Principle in Government-Binding Theory \[Chomsky 
1981\]). 
One of the most important contributions has been the view that argument structure 
is highly structured independent of the syntax. Williams's (1981) distinction between 
external and internal arguments and Grimshaw's proposal for a hierarchically struc- 
tured representation (Grimshaw 1990) provide us with the basic syntax for one aspect 
of a word's meaning. 
The argument structure for a word can be seen as a minimal specification of 
its lexical semantics. By itself, it is certainly inadequate for capturing the semantic 
characterization of a lexical item, but it is a necessary component. 
5.2 Event Structure 
As mentioned above, the theory of decomposition being outlined here is based on the 
central idea that word meaning is highly structured, and not simply a set of semantic 
features. Let us assume this is the case. Then the lexical items in a language will 
essentially be generated by the recursive principles of our semantic theory. One level 
of semantic description involves an event-based interpretation of a word or phrase. 
I will call this level the event structure of a word (cf. Pustejovsky 1991; Moens and 
Steedman 1988). The event structure of a word is one level of the semantic specification 
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Computational Linguistics Volume 17, Number 4 
for a lexical item, along with its argument structure, qualia structure, and inheritance 
structure. Because it is recursively defined on the syntax, it is also a property of phrases 
and sentences. 8 
I will assume a sortal distinction between three classes of events: states (eS), pro- 
cesses (8), and transitions (eT). Unlike most previous ,;ortal classifications for events, 
I will adopt a subeventual analysis or predicates, as argued in Pustejovsky (1991) and 
independently proposed in Croft (1991). In this view, an event sort such as e T may 
be decomposed into two sequentially structured subevents, (ee,sS). Aspects of the 
proposal will be introduced as needed in the following discussion. 
6. A Theory of Qualia 
In Section 5, I demonstrated how most of the lexical semantics research has con- 
centrated on verbal semantics. This bias influences our analyses of how to handle 
ambiguity and certain noncompositional structures. Therefore, the only way to relate 
the different senses for the verbs in the examples below was to posit separate entries. 
Example 22 
a. John baked the potato. 
(bake1 = change(x, State(y))) 
b. John baked the cake. 
(bake2 = create(x,y)) 
Example 23 
a. Mary hammered the metal. 
(hammer1 = change(x, State(y))) 
b. Mary hammered the metal fiat. 
(hammer2 = cause(x, Become(fiat(y)))) 
Example 24 
a. John wiped the table. 
(wipe1 = change (x, State (y) )) 
b. John wiped the table clean. 
(wipe2 = cause(x, Become(clean(y)))) 
Example 25 
a. Mary ran yesterday. 
(run1 = move(x)) 
b. Mary ran to the store yesterday. 
(run2 = go-to(x, y)) 
• Although the complement types selected by bake in 22, for example, are semantically 
related, the two word senses are clearly distinct and therefore must be lexically distin- 
guished. According to the sense enumeration view, the same argument holds for the 
verbs in 23-25 as well. 
8 This proposal is an extension of ideas explored by Bach (1986), Higginbotham (1985), and Allen (1984). 
For a full discussion, see Pustejovsky (1988, 1991). See Tenny (1987) for a proposal on how aspectual distinctions are mapped to the syntax. 
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James Pustejovsky The Generative Lexicon 
A similar philosophy has lead linguists to multiply word senses in constructions 
involving Control and Equi-verbs, where different syntactic contexts necessitate dif- 
ferent semantic types? 
Example 26 
a. It seems that John likes Mary. 
b. John seems to like Mary. 
Example 27 
a. Mary prefers that she come. 
b. Mary prefers to come. 
Normally, compositionality in such structures simply refers to the application of the 
functional element, the verb, to its arguments. Yet, such examples indicate that in 
order to capture the systematicity of such ambiguity, something else is at play, where 
a richer notion of composition is operative. What then accounts for the polysemy of 
the verbs in the examples above? 
The basic idea I will pursue is the following. Rather than treating the expressions 
that behave as arguments to a function as simple, passive objects, imagine that they 
are as active in the semantics as the verb itself. The product of function application 
would be sensitive to both the function and its active argument. Something like this 
is suggested in Keenan and Faltz (1985), as the Meaning-Form Correlation Principle. I 
will refer to such behavior as cocompositionality (see below). What I have in mind can 
best be illustrated by returning to the examples in 28. 
Example 28 
a. John baked the potato. 
b. John baked the cake. 
Rather than having two separate word senses for a verb such as bake, suppose there 
is simply one, a change-of-state reading. Without going into the details of the analysis, 
let us assume that bake can be lexically specified as denoting a process verb, and is 
minimally represented as Example 29. l° 
Example 29 
Lexical Semantics for bake: n 
)~y)~x)~eP\[bake(e P) A agent(e P, x) A object(e P, y)\] 
In order to explain the shift in meaning of the verb, we need to specify more clearly 
what the lexical semantics of a noun is. I have argued above that lexical semantic theory 
must make a logical distinction between the following qualia roles: the constitutive, 
formal, telic, and agentive roles. Now let us examine these roles in more detail. One 
can distinguish between potato and cake in terms of how they come about; the former 
9 For example, Dowty (1985) proposes multiple entries for verbs taking different subcategorizations. 
Gazdar et al. (1985), adopting the analysis in Klein and Sag (1985), propose a set of lexical type-shifting 
operations to capture sense relatedness. We return to this topic below. 
10 I will be assuming a Davidsonian-style representation for the discussion below. Predicates in the 
language are typed for a particular event-sort, and thematic roles are treated as partial functions over 
the event (cf. Dowty 1989 and Chierchia 1989). 
11 More precisely, the process e p should reflect that it is the substance contained in the object x that is 
affected. See footnote 20 for explanation. 
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Computational Linguistics Volume 17, Number 4 
is a natural kind, while the latter is an artifact. Knowledge of an object includes not 
just being able to identify or refer, but more specifically, being able to explain how an 
artifact comes into being, as well as what it is used for; the denotation of an object 
must identify these roles. Thus, any artifact can be identified with the state of being 
that object, relative to certain predicates. 
As is well known from work on event semantics and Aktionsarten, it is a general 
property of processes that they can shift their event type to become a transition event 
(cf. Hinrichs 1985; Moens and Steedman 1987; and Krifka 1987). This particular fact 
about event structures, together with the semantic distinction made above between 
the two object types, provides us with an explanation for what I will refer to as the 
logical polysemy of verbs such as bake. 
As illustrated in Example 30a, when the verb takes as its complement a natural 
kind such as potato, the resulting semantic interpretation is unchanged; i.e., a process 
reading of a state-change. This is because the noun does not "project" an event struc- 
ture of its own. That is, relative to the process of baking, potato does not denote an 
event-type. 12 
Example 30 
a. bake as Process: 
3eP\[bake(e P) A agent(~,j) A object(e P, a-potato)\] 
b. 
P 
John baked 
V 
VP 
a potato 
NP 
What is it, then, about the semantics of cake that shifts this core meaning of bake 
from a state-change predicate to its creation sense? As just suggested, this additional 
meaning is contributed by specific lexical knowledge we have about artifacts, and 
cake in particular; namely, there is an event associated with that object's "coming 
into being," in this case the process of baking. Thus, just as a verb can select for an 
argument-type, we can imagine that an argument is itself able to select the predicates 
that govern it. I will refer to such constructions as cospecifications. Informally, relative 
to the process bake, the noun cake carries the selectional information that it is a process 
of "baking" that brings it about. 13 
12 However, relative to the process of growing, the noun potato does denote an event: 
1. Mary grew the potato. 
13 Other examples of cospecifications are: a. read a book, b. smoke a cigarette, c. mail a letter, d. deliver a lecture, and e. take a bath. 
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James Pustejovsky The Generative Lexicon 
We can illustrate this schematically in Example 31, where the complement effec- 
tively acts like a "stage-level" event predicate (cf. Carlson 1977) relative to the process 
event-type of the verb (i.e. a function from processes to transitions, <P,T>). 14 The 
change in meaning in 31 comes not from the semantics of bake, but rather in com- 
position with the complement of the verb, at the level of the entire verb phrase. The 
"creation" sense arises from the semantic role of cake that specifies it is an artifact (see 
below for discussion). 
Example 31 
a. bake as a derived Transition: 15 
3e P, eS\[create(e P, e s) A bake(e P ) A agent(eP,j) A object(e P, x) 
A cake(e s) A object(e s, x)\] 
b. 
T 
P 
John baked 
V 
<P,T> 
a cake 
NP 
VP 
Thus, we can derive both word senses of verbs like bake by putting some of the 
semantic weight on the NP. This view suggests that, in such cases, the verb itself is 
not polysemous. Rather, the sense of "create" is part of the meaning of cake by virtue 
of it being an artifact. The verb appears polysemous because certain complements add 
to the basic meaning by virtue of what they denote. We return to this topic below, 
There are several interesting things about such collocations. First, because the complement "selects" 
the verb that governs it (by virtue of knowledge of what is done to the object), the semantics of the 
phrase is changed. The semantic "connectedness," as it were, is tighter when cospecification obtains. In 
such cases, the verb is able to successfully drop the dative PP argument, as shown below in (1). When 
the complement does not select the verb governing it, dative-drop is ungrammatical as seen in (2) 
(although there are predicates selected by these nouns; e.g. keep a secret, read a book, and play a record). 
la. Romeo gave the lecture. 
b.Hamlet mailed a letter. 
c. Cordelia told a story. 
d.Gertrude showed a movie. 
e.Mary asked a question. 
2a. *Bill told the secret. 
b.*Mary gave a book. 
c. *Cordelia showed the record. 
For discussion see Pustejovsky (in press). 
14 cf. Pustejovsky (forthcoming) for details. 
15 As mentioned in footnote 11, this representation is incomplete. See footnote 20 for semantics of bake. 
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and provide a formal treatment for how the nominal semantics is expressed in these 
examples. 
Similar principles seem to be operating in tile resultative constructions in Exam- 
ples 23 and 24; namely, a systematic ambiguity is the result of principles of semantic 
composition rather than lexical ambiguity of the verbs. For example, the resultative 
interpretations for the verbs hammer in 23(b) and wipe in 24(b) arise from a similar 
operation, where both verbs are underlyingly specified with an event type of pro- 
cess. The adjectival phrases fiat and clean, although clearly stative in nature, can also 
be interpreted as stage-level event predicates (cf. Dowty 1979). Notice, then, how 
the resultative construction requires no additional word sense for the verb, nor any 
special semantic machinery for the resultative interpretation to be available. Schemat- 
ically, this is shown in Example 32. 
Example 32 
T 
P <P,T> 
I 
John hammer the metal flat 
V NP AP 
VP 
In fact, this analysis explains why it is that only process verbs participate in the re- 
sultative construction, and why the resultant phrase (the adjectival phrase) must be a 
subset of the states, namely, stage-level event predicates. Because the meaning of the 
sentence in 32 is determined by both function application of hammer to its arguments 
and function application of fiat to the event-type of the verb, this is an example of 
cocompositionality (cf. Pustejovsky \[forthcoming\] for discussion). 
Having discussed some of the behavior of logical polysemy in verbs; let us con- 
tinue our discussion of lexical ambiguity with the issue of metonymy. Metonymy, where 
a subpart or related part of an object "stands for" the object itself, also poses a prob- 
lem for standard denotational theories of semantics. To see why, imagine how our 
semantics could account for the "reference shifts" of the complements shown in Ex- 
ample 33.16 
Example 33 
a. Mary enjoyed the book. 
b. Thatcher vetoed the channel tunnel. (Cf. Hobbs 1987) 
c. John began a novel. 
16 See Nunberg (1978) and Fauconnier (1985) for very clear discussions of the semantics of metonymy 
and the nature of reference shifts. See Wilks (1975) and Fass (1988) for computational models of 
metonymic resolution. 
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James Pustejovsky The Generative Lexicon 
The complements of enjoy in 33(a) and begin in 33(c) are not what these verbs normally 
select for semantically, namely a property or action. Similarly, the verb veto normally 
selects for an object that is a legislative bill or a suggestion. Syntactically, these may 
simply be additional subcategorizations, but how are these examples related semanti- 
cally to the normal interpretations? 
I suggest that these are cases of semantic type coercion (cf. Pustejovsky 1989a), 
where the verb has coerced the meaning of a term phrase into a different semantic 
type. Briefly, type coercion can be defined as follows: 17 
Definition 
Type Coercion: A semantic operation that converts an argument to the type that is 
expected by a function, where it would otherwise result in a type error. 
In the case of 33(b), it is obvious that what is vetoed is some proposal relating to 
the object denoted by the tunnel. In 33(a), the book is enjoyed only by virtue of some 
event or process that involves the book, performed by Mary. It might furthermore be 
reasonable to assume that the semantic structure of book specifies what the artifact is 
used for; i.e. reading. Such a coercion results in a word sense for the NP that I will 
call logical metonymy. Roughly, logical metonymy occurs when a logical argument (i.e. 
subpart) of a semantic type that is selected by some function denotes the semantic 
type itself. 
Another interesting set of examples involves the possible subjects of causative 
verbs. TM Consider the sentences in Examples 34 and 35. 
Example 34 
a. Driving a car in Boston frightens me. 
b. To drive a car in Boston frightens me. 
c. Driving frightens me. 
d. John's driving frightens me. 
e. Cars frighten me. 
f. Listening to this music upsets me. 
g. This music upsets me. 
h. To listen to this music would upset me. 
Example 35 
a. John killed Mary. 
b. The gun killed Mary. 
c. John's stupidity killed Mary. 
d. The war killed Mary. 
e. John's pulling the trigger killed Mary. 
As these examples illustrate, the syntactic argument to a verb is not always the same 
logical argument in the semantic relation. Although superficially similar to cases of 
general metonymy (cf. Lakoff and Johnson 1982; Nunberg 1978), there is an interesting 
systematicity to such shifts in meaning that we will try to characterize below as logical 
metonymy. 
171 am following Cardelli and Wegener (1985) and their characterization of polyrnorphismic behavior. 18 See Verma and Mohanan (1991) for an extensive survey of experiencer subject constructions in different 
languages. 
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The sentences in 34 illustrate the various syntactic consequences of metonymy and 
coercion involving experiencer verbs, while those in 35 show the different metonymic 
extensions possible from the causing event in a killing. The generalization here is that 
when a verb selects an event as one of its arguments, type coercion to an event will per- 
mit a limited range of logical metonymies. For example, in sentences 34(a,b,c,d,f,h), the 
' entire event is directly referred to, while in 34(e,g) only a participant from the coerced 
event reading is directly expressed. Other examples of coercion include "concealed 
questions" 36 and "concealed exclamations" 37 (cf. Grimshaw 1979; Elliott 1974). 
Example 36 
a. John knows the plane's arrival time. 
(= what time the plane will arrive) 
b. Bill figured out the answer. 
(= what the answer is) 
Example 37 
a. John shocked me with his bad behavior. 
(= how bad his behavior is) 
b. You'd be surprised at the big cars he buys. 
(= how big the cars he buys are) 
That is, although the italicized phrases syntactically appear as NPs, their semantics is 
the same as if the verbs had selected an overt question or exclamation. 
In explaining the behavior of the systematic ambiguity above, I made reference 
to properties of the noun phrase that are not typical semantic properties for nouns 
in linguistics; e.g., artifact, natural kind. In Pustejovsky (1989b) and Pustejovsky and 
Anick (1988), I suggest that there is a system of relations that characterizes the seman- 
tics of nominals, very much like the argument structure of a verb. I called this the 
Qualia Structure, inspired by Aristotle's theory of explanation and ideas from Moravc- 
sik (1975). Essentially, the qualia structure of a noun determines its meaning as much 
as the list of arguments determines a verb's meaning. The elements that make up a 
qualia structure include notions such as container, space, surface, figure, artifact, and 
so on. 19 
As stated earlier, there are four basic roles that constitute the qualia structure for 
a lexical item. Here I will elaborate on what these roles are and why they are useful. 
They are given in Example 38, where each role is defined, along with the possible 
values that these roles may assume. 
Example 38 
The Structure of Qualia: 
1. Constitutive Role: the relation between an object and its constituents, or 
proper parts. 
• Material 
• Weight 
• Parts and component elements 
19 These components of an object's denotation have long been considered crucial for our commonsense 
understanding of how things interact in the world. Cf. Hayes (1979), Hobbs et al. (1987), and Croft 
(1991) for discussion of these qualitative aspects of meaning. 
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James Pustejovsky The Generative Lexicon 
2. Formal Role: that which distinguishes the object within a larger domain. 
• Orientation 
• Magnitude 
• Shape 
• Dimensionality 
• Color 
• Position 
3. Telic Role: purpose and function of the object. 
. 
Purpose that an agent has in performing an act 
Built-in function or aim that specifies certain activities 
Agentive Role: factors involved in the origin or "bringing about" of an 
object. 
• Creator 
• Artifact 
• Natural Kind 
• Causal Chain 
When we combine the qualia structure of a NP with the argument structure of a verb, 
we begin to see a richer notion of compositionality emerging, one that looks very much 
like object-oriented approaches to programming (cf. Ingria and Pustejovsky 1990). 
To illustrate these structures at play, let us consider a few examples. Assume 
that the decompositional semantics of a nominal includes a specification of its qualia 
structure: 
Example 39 
Object( Const, Form, Telic, Agent) 
For example, a minimal semantic description for the noun novel will include values for 
each of these roles, as shown in Example 40, where *x* can be seen as a distinguished 
variable, representing the object itself. 
Example 40 
novel(*x*) 
Const: narrative(*x*) 
Form: book(*x*), disk(*x*) 
Telic: read(T,y,*x*) 
Agentive: artifact(*x*), write(T,z,*x*) 
This structures our basic knowledge about the object: it is a narrative; typically in 
the form of a book; for the purpose of reading (whose event type is a transition); 
and is an artifact created by a transition event of writing. Observe how this structure 
differs minimally, but significantly, from the qualia structure for the noun dictionary in 
Example 41. 
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Example 41 
dictionary(*x*) 
Const: alphabetized-listing(*x*) 
Form: book(*x*), disk(*x*) 
Telic: reference(P,y,*x*) 
Agentive: artifact(*x*), compile(T,z,*x~) 
Notice the differences in the values for the constitutive and telic roles. The purpose of 
a dictionary is an activity of referencing, which has an event structure of a process. 
I will now demonstrate that such structured information is not only useful for 
nouns, but necessary to account for their semantic behavior. I suggested earlier, that 
for cases such as 33, repeated below, there was no need to posit a separate lexical entry 
for each verb, where the syntactic and semantic types had to be represented explicitly. 
Example 42 
a. Mary enjoyed the book. 
b. Thatcher vetoed the channel tunnel. 
c. John began a novel. 
Rather, the verb was analyzed as coercing its complement to the semantic type it ex- 
pected. To illustrate this, consider 42(c). The type for begin within a standard typed 
intensional logic is <VP, <NP, S>>, and its lexical semantics is similar to that of other 
subject control verbs (cf. Klein and Sag \[1985\] for discussion). 
Example 43 
APAT~7 ~Ax\[begin'(P(x*))(x*)\] 
Assuming an event structure such as that of Krifka (1987) or Pustejovsky (1991), 
we can convert this lexical entry into a representation consistent with a logic making 
use of event-types (or sorts) by means of the following meaning postulate. 2° 
Example 44 
VPVxl .. . Xn \[\] \[P¢ (xl) . .. (Xn) ~ 3e ~ \[P (xl) . .. (x,) (e ~ )\]\] 
This allows us to type the verb begin as taking a transition event as its first argument, 
represented in Example 45. 
Example 45 
APT A 7979 Ax\[begin ' ( PT (X*)) (X*)\] 
Because the verb requires that its first argument be of type transition the complement 
in 33(c) will not match without some sort of shift. It is just this kind of context where 
the complement (in this case a novel) is coerced to another type. The coercion dictates to 
the complement that it must conform to its type specification and the qualia roles may 
20 It should be pointed out that the lexical structure for the verb bake given above in 30 and 31 can more 
properly be characterized as a process acting on various qualia of the arguments. 
1. AyAxAee eS\[bake(e e) A agent(d, x) A object(d, Const(y) ) A cake(e s) A object(e s, Formal(x))\] 
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James Pustejovsky The Generative Lexicon 
in fact have values matching the correct type. For purposes of illustration, the qualia 
structure for novel from 41 can be represented as the logical expression in Example 46. 
Example 46 
novel translates into: 
)~x\[novel(x) A Const(x)= narrative'(x) A 
Form(x) = book'(x) A 
Telic(x) = ,~y, eT\[read' (x)(y)(er)\] A 
Agent(x) = ,~y, er\[write'(x)(y)(eT)\]\] 
The coercion operation on the complement in the above examples can be seen as a 
request to find any transition event associated with the noun. As we saw above, the 
qualia structure contains just this kind of information. 
We can imagine the qualia roles as partial functions from a noun denotation into its 
subconstituent denotations. For our present purposes, we abbreviate these functions 
as Q~, Qo QT, QA. When applied, they return the value of a particular qualia role. For 
example, the purpose of a novel is for reading it, shown in 47(a), while the mode of 
creating a novel is by writing it, represented in 47(b). 
Example 47 
a. QT(novel) = &y~ eT\[read(x)(y)(er)\] 
b. QA (novel) = )~y, eT\[write(x) (y) (eT)\] 
As the expressions in 47 suggest, there are, in fact, two obvious interpretations for this 
sentence in 42(c). 
Example 48 
a. John began to read a novel. 
b. John began to write a novel. 
One of these is selected by the coercing verb, resulting in a complement that has a 
event-predicate interpretation, without any syntactic transformations (cf. Pustejovsky 
\[1989a\] for details), al The derivation in 49(a) and the structure in 49(b) show the effects 
of this coercion on the verb's complement, using the telic value of novel. 22 
21 There are, of course, an indefinite number of interpretations, depending on pragmatic factors and 
various contextual influences. But I maintain that there are only a finite number of default 
interpretations available in such constructions. These form part of the lexical semantics of the noun. 
Additional evidence for this distinction is given in Pustejovsky and Anick (1988) and Briscoe et al. 
(1990). 
22 Partee and Rooth (1983) suggest that all expressions in the language can be assigned a base type, while 
also being associated with a type ladder. Pustejovsky (1989a) extends this proposal, and argues that 
each expression c~ may have available to it, a set of shifting operators, which we call Ga, which operate 
over an expression, changing its type and denotation. By making reference to these operators directly 
in the rule of function application, we can treat the functor polymorphically, as illustrated below. 
1. Function Application with Coercion (FAc): 
If c~ is of type (b, a}, and fl is of type c, then 
(a) if type c = b, then c~(fl) is of type a. 
(b) if there is a ¢ C ~,~ such that cr(fl) results in an expression of type b, then 
c~(a(fl)) is of type a. 
(c) otherwise a type error is produced. 
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Computational Linguistics Volume 17, Number 4 
Example 49 
a. John began a novel. 
b. begin'(QT(a novel))(John) 
c. begin'(Ax, e T \[read(a novel)(x)(eT)\]) (John) 
d. John{Ax\[begin'(Ax~ eT\[read(a novel)(x)(eT)\](x*))(x*)\]} 
e. John{ Ax\[begin'( AeT\[read(a novel)(x" )(eT)\])(x* )\]} 
f. begin'(Ae T \[read(a novel) (John) (eT)\]) (John) 
g. 
Mary begin a novel 
NP' < VP, < NP, S >> NP' 
< NP, S > 
S 
The fact that this is not a unique interpretation of the elliptical event predicate is in 
some ways irrelevant to the notion of type coercion. That there is some event involving 
the complement is required by the lexical semantics of the governing verb and the rules 
of type well-formedness, and although there are many ways to act on a novel, I argue 
that certain relations are "privileged" in the lexical semantics of the noun. It is not the 
role of a lexical semantic theory to say what readings are preferred, but rather which 
are available. 23 
Assuming the semantic selection given above for begin is correct, we would predict 
that, because of the process event-type associated with the telic role for dictionary, there 
is only one default interpretation for the sentence in 50; namely, the agentive event of 
"compiling." 
23 There are interesting differences in complement types between finish and complete. The former takes 
both NP and a gerundive VP, while the latter takes only an NP (cf. for example, Freed \[1979\] for 
discussion). 
la. John finished the book. 
b. John finished writing the book. 
2a. John completed the book. 
b. *John completed writing the book. 
The difference would indicate that, contrary to some views (e.g. Wierzbicka \[1988\] and Dixon \[1991\]), 
lexical items need to carry both syntactic and semantic selectional information to determine the range 
of complements they may take. Notice here also that complete tends to select the agentive role value for 
its complement and not the telic role. The scope of semantic selection is explored at length in 
Pustejovsky (forthcoming). 
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James Pustejovsky The Generative Lexicon 
Example 50 
a. Mary began a dictionary. (Agentive) 
b. ?? Mary began a dictionary. (Telic) 
Not surprisingly, when the noun in complement position has no default interpretation 
within an event predicate -- as given by its qualia structure -- the resulting sentence 
is extremely odd. 
Example 51 
a. *Mary began a rock. 
b. ??John finished the flower. 
The semantic distinctions that are possible once we give semantic weight to lexical 
items other than verbs are quite wide-ranging. The next example I will consider con- 
cerns scalar modifiers, such as fast, that modify different predicates depending on the 
head they modify. If we think of certain modifiers as modifying only a subset of the 
qualia for a noun, then we can view fast as modifying only the telic role of an object. 
This allows us to go beyond treating adjectives such as fast as intersective modifiers 
for example, as Ax\[car'(x) Afast'(x)\]. Let us assume that an adjective such as fast is a 
member of the general type (N, N), but can be subtyped as applying to the Telic role 
of the noun being modified. That is, it has as its type, (IN Telic\],N}. This gives rise 
directly to the different interpretations in Example 52. 
Example 52 
a. a fast car: driving 
QT (car) = AxAyAeP\[ drive(x)(y)(e v) \] 
b. a fast typist: typing 
Qr(typist) = AxAeP\[ type(x)(e P) \] 
c. a fast motorway: traveling 
Qv(motorway) = AxAeV\[ travel(cars)(e P) A on(x)(cars)(e v) \] 
These interpretations are all derived from a single word sense for fast. Because the 
lexical semantics for this adjective indicates that it modifies the telic role of the noun, 
it effectively acts as an event predicate rather than an attribute over the entire noun 
denotation, as illustrated in Example 53 for fast motorway (cf. Pustejovsky and Boguraev 
\[1991\] for discussion). 
Example 53 
Ax \[mot orway ( x ) . . . \[Tel ic ( x ) = AeV \[ travel (cars ) ( e P) 
A on(x)(cars)(e p) A fast(e P) \]\]\] 
As our final example of how the qualia structure contributes to the semantic in- 
terpretation of a sentence, observe how the nominals window and door in Examples 54 
and 55 carry two interpretations (cf. Lakoff \[1987\] and Pustejovsky and Anick \[1988\]): 
Example 54 
a. John crawled through the window. 
b. The window is closed. 
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Computational Linguistics Volume 17, Number 4 
Example 55 
a. Mary painted the door. 
b. Mary walked through the door. 
Each noun appears to have two word senses: a physical object denotation and an 
aperture denotation. Pustejovsky and Anick (1988) characterize the meaning of such 
"Double Figure-Ground" nominals as inherently relational, where both parameters are 
logically part of the meaning of the noun. In terms of the qualia structure for this class 
of nouns, the formal role takes as its value the Figure of a physical object, while the 
constitutive role assumes the Invert-Figure value of an aperture. 24 
Example 56 
Lexical Semantics for door: 
door(*x*,*y*) 
Const: aperture(*y*) 
Form: phys-obj(*x*) 
Telic: pass-through(T,z,*y*) 
Agentive: artifact(*x*) 
The foregrounding or backgrounding of a nominal's qualia is very similar to argument 
structure-changing operations for verbs. That is, in 55(a), paint applies to the formal 
role of the door, while in 55(b), through will apply to the constitutive interpretation of 
the same NP. The ambiguity with such nouns is a logical one, one that is intimately 
linked to the semantic representation of the object itself. The qualia structure, then, is 
a way of capturing this logical polysemy. 
In conclusion, it should be pointed out that the entire lexicon is organized around 
such logical ambiguities, which Pustejovsky and Anick (1988) call Lexical Conceptual 
Paradigms. Pustejovsky (forthcoming) distinguishes tlhe following systems and the 
paradigms that lexical items fall into: 
Example 57 
a. Count/Mass Alternations 
b. Container/Containee Alternations 
c. Figure/Ground Reversals 
d. Product/Producer Diathesis 
e. Plant/Fruit Alternations 
f. Process/Result Diathesis 
g. Object/Place Reversals 
h. State/Thing Alternations 
i. Place/People 
Such paradigms provide a means for accounting for the systematic ambiguity that may 
exist for a lexical item. For example, a noun behaving according to paradigm 57(a) 
24 There are many such classes of nominals, both two-dimensional such as those mentioned in the text, 
and three-dimensional, such as "room," "fireplace," and "pipe." They are interesting semantically, 
because they are logically ambiguous, referring to either the object or the aperture, but not both. 
Boguraev and Pustejovsky (forthcoming) show how these logical polysemies are in fact encoded in dictionary definitions for these words. 
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James Pustejovsky The Generative Lexicon 
exhibits a logical polysemy involving packaging or grinding operators; e.g., haddock 
or lamb (cf. Copestake and Briscoe \[1991\] for details). 
7. Lexical Inheritance Theory 
In previous sections, I discussed lexical ambiguity and showed how a richer view of 
lexical semantics allows us to view a word's meaning as being flexible, where word 
senses could arise generatively by composition with other words. The final aspect of 
this flexibility deals with the logical associations a word has in a given context; that is, 
how this semantic information is organized as a global knowledge base. This involves 
capturing both the inheritance relations between concepts and, just as importantly, 
how the concepts are integrated into a coherent expression in a given sentence. 
I will assume that there are two inheritance mechanisms at work for representing 
the conceptual relations in the lexicon: fixed inheritance and projective inheritance. The 
first includes the methods of inheritance traditionally assumed in AI and lexical re- 
search (e.g. Roberts and Goldstein 1977; Brachman and Schmolze 1985; Bobrow and 
Winograd 1977); that is, a fixed network of relations, which is traversed to discover 
existing related and associated concepts (e.g. hyponyms and hypernyms). In order to 
arrive at a comprehensive theory of the lexicon, we need to address the issue of global 
organization, and this involves looking at the various modes of inheritance that exist 
in language and conceptualization. Some of the best work addressing the issue of how 
the lexical semantics of a word ties into its deeper conceptual structure includes that 
of Hobbs et al. (1987) and Wilks (1975), while interesting work on shared information 
structures in NLP domains is that of Flickinger et al. (1985) and Evans and Gazdar 
(1989, 1990). 
In addition to this static representation, I will introduce another mechanism for 
structuring lexical knowledge, the projective inheritance, which operates generatively 
from the qualia structure of a lexical item to create a relational structure for ad hoc 
categories. Both are necessary for projecting the semantic representations of individual 
lexical items onto a sentence level interpretation. The discussion here, however, will 
be limited to a description of projective inheritance and the notion of "degrees of 
prototypicality" of predication. I will argue that such degrees of salience or coherence 
relations can be explained in structural terms by examining a network of related lexical 
items. 25 
I will illustrate the distinction between these mechanisms by considering the two 
sentences in Example 58, and their relative prototypicality. 
Example 58 
a. The prisoner escaped last night. 
b. The prisoner ate dinner last night. 
Both of these sentences are obviously well-formed syntactically, but there is a definite 
sense that the predication in 58(a) is "tighter" or more prototypical than that in 58(b). 
What would account for such a difference? Intuitively, we associate prisoner with an 
escaping event more strongly than an eating event. Yet this is not information that 
comes from a fixed inheritance structure, but is rather usually assumed to be com- 
monsense knowledge. In what follows, however, I will show that such distinctions 
25 Anick and Pustejovsky (1990) explore how metrics such as association ratios can be used to statistically 
measure the notions of prototypicality mentioned here. 
433 
Computational Linguistics Volume 17, Number 4 
can be captured within a theory of lexical semantics by means of generating ad hoc 
categories. 
First, we give a definition for the fixed inheritance structure of a lexical item (cf. 
Touretzky 1986). Let Q and P be concepts in our model of lexical organization. Then: 
Definition 
A sequence (Q1, P1,..., Pn) is an inheritance path, which can be read as the conjunction 
of ordered pairs {(xl,yi) \[ 1 < i < n}. 
Furthermore, following Touretsky, from this we can define the set of concepts that lie 
on an inheritance path, the conclusion space. 
Definition 
The conclusion space of a set of sequences • is the set of all pairs (Q, P) such that a 
sequence (Q,..., P) appears in q~. 
From these two definitions we can define the traditional is-a relation, relating the 
above pairs by a generalization operator, ~G, 26 as well as other relations that I will not 
discuss. 27 
Let us suppose that, in addition to these fixed relational structures, our semantics 
allows us to dynamically create arbitrary concepts through the application of certain 
transformations to lexical meanings. For example, for any predicate, Q -- e.g. the 
value of a qualia role -- we can generate its opposition, ~Q (cf. Pustejovsky 1991). 
By relating these two predicates temporally we can generate the arbitrary transition 
events for this opposition (cf. Wright 1963): 
Example 59 
a. ~Q(x) <_ Q(x) 
b. Q(x) < -~Q(x) 
c. Q(x) < Q(x) 
d. ~Q(x) < -~Q(x) 
Similarly, by operating over other qualia role values we can generate semantically 
related concepts. I will call any operator that performs such an operation a projective 
transformation, and define them below: 
Definition 
A projective transformation, Tr, on a predicate Q1 generates a predicate, Q2, such that 
7r(Q1) = Q2, where Q2 ~ ~. The set of transformations includes: 7, negation, _<, 
temporal precedence, >_, temporal succession, =, temporal equivalence, and act, 
an operator adding agency to an argument. 
Intuitively, the space of concepts traversed by the application of such operators 
will be related expressions in the neighborhood of the original lexical item. This space 
can be characterized by the following two definitions: 
26 See, for example, Michalski (1983) and Smolka (1988) for a treatment making use of subsorts. 27 Such relations include not only hypernymy and hopyonymy, but also troponymy, which relates verbs 
by manner relations (cf. Miller 1985; Beckwith et al. 1989; Miller and Fellbaum 1991. 
434 
James Pustejovsky The Generative Lexicon 
Definition 
A series of applications of transformations, ~rl,..., 7rn, generates a sequence of predi- 
cates, (Q1,..., Qnl, called the projective expansion of Q1, P(Q1). 
Definition 
The projective conclusion space, P(@R), is the set of projective expansions generated 
from all elements of the conclusion space, ~, on role R of predicate Q: as: P(~R) = 
{(P(Q1),P(Qn)> \[ (QI,...,Qn) E ~R}. 
From this resulting representation, we can generate a relational structure that can 
be considered the set of ad hoc categories and relations associated with a lexical item 
(cf. Barselou 1983). 
Using these definitions, let us return to the sentences in Example 58. I will assume 
that the noun prisoner has a qualia structure such as that shown in 60. 
Example 60 
Qualia Structure of prisoner(x): 
prisoner(*x*) 
Form: human(*x*) 
Telic: \[confine(y,*x*) location(*x*,prison)\] 
Furthermore, I assume the following lexical structure for escape. 
Example 61 
Lexical Semantics for escape: 
AxAeT3e p, eS\[escape(e T) A act(e P) A confined(d) A agent(e p, x) 
A -~confined(e s) A object(e s, x)\] 
Using the representation in 60 above, I now trace part of the derivation of the 
projective conclusion space for prisoner. Inheritance structures are defined for each 
qualia role of an element. In the case above, values are specified for only two roles. 
For each role, R, we apply a projective transformation 7r onto the predicate Q that is 
the value of that role. For example, from the telic role of prisoner we can generalize (e.g. 
drop the conjunct) to the concept of being confined. From this concept, we can apply the 
negation operator, generating the predicate opposition of not-confined and confined. To 
this, we apply the two temporal operators, < and >, generating two states: free before 
capture and free after capture. Finally, to these concepts, if we apply the operator act, 
varying who is responsible for the resulting transition event, we generate the concepts: 
turn in, capture, escape, and release. 
Example 62 
Projecting on Telic Role of prisoner: 
a. ~c: \[confine(y, x) A loc(x, prison)\] ~ confine(y, x) 
b. 7:BE1 \[-~confine(E1, y, x)\] 
c. 3E2 \[confine(E2, y, x)\] 
d. ~: E1 _< E2 = T1 
e. <_: E2 <_ E1 = T2 
f. act: act(x, T1) = "turn in" 
435 
Computational Linguistics Volume 17, Number 4 
g. act: act(y, T1) = "capture" 
h. act: act(x, T2) = "escape" 
i. act: act(y, T2) = "release" 
These relations constitute the projective conclusion space for the telic role of prisoner 
relative to the application of the transformations mentioned above. Similar operations 
on the formal role will generate concepts such as die and kill. Generating such structures 
for all items in a sentence during analysis, we can take those graphs that result in no 
contradictions to be the legitimate semantic interpretations of the entire sentence. 
Let us now return to the sentences in Example 58. It is now clear why these two 
sentences differ in their prototypicality (or the relevance conditions on their predi- 
cation). The predicate eat is not within the space of related concepts generated from 
the semantics of the NP the prisoner; escape, however, did fall within the projective 
conclusion space for the Telic role of prisoner, as shown in Example 63. 
Example 63 
Conclusion Space for (58): 
escape c P(~T(prisoner)) 
eat ~ P( ~T(prisoner) ) 
This is illustrated in Example 64 below. 
Example 64 
release(T, y, *x*) escape(T, *x*) capture(T, y, *x*) turn-in(T, *x*) 
81 ~ S2 82 _~ $1 
-~confined(S2, y, *x*) 
I 
confined(S1, y, *x*) 
Formal Telic escape(T, *x*) 
the prisoner escaped 
I I 
Det N V 
NP VP ~ 
jf 
S 
We can therefore use such a procedure as one metric for evaluating the "proximity" 
of a predication (Quillian 1968; Hobbs 1982). In the examples above, the difference 
436 
James Pustejovsky The Generative Lexicon 
in semanticality can now be seen as a structural distinction between the semantic 
representations for the elements in the sentence. 
In this section, I have shown how the lexical inheritance structure of an item 
relates, in a generative fashion, the decompositional structure of a word to a much 
larger set of concepts that are related in obvious ways. What we have not addressed, 
however, is how the fixed inheritance information of a lexical item is formally derivable 
during composition. This issue is explicitly addressed in Briscoe et al. (1990) as well 
as Pustejovsky and Briscoe (1991). 
8. Conclusion 
In this paper I have outlined a framework for lexical semantic research that I believe 
can be useful for both computational linguists and theoretical linguists alike. I argued 
against the view that word meanings are fixed and inflexible, where lexical ambigu- 
ity must be treated by multiple word entries in the lexicon. Rather, the lexicon can 
be seen as a generative system, where word senses are related by logical operations 
defined by the well-formedness rules of the semantics. In this view, much of the lex- 
ical ambiguity of verbs and prepositions is eliminated because the semantic load is 
spread more evenly throughout the lexicon to the other lexical categories. I described 
a language for structuring the semantic information carried by nouns and adjectives, 
termed Qualia structure, as well as the rules of composition that allow this information 
to be incorporated into the semantic interpretation of larger expressions, including 
explicit methods for type coercion. Finally, I discussed how these richer lexical repre- 
sentations can be used to generate projective inheritance structures that connect the 
conceptual information associated with lexical items to the global conceptual lexicon. 
This suggests a way of accounting for relations such as coherence and the prototyp- 
icality of a predication. Although much of what I have presented here is incomplete 
and perhaps somewhat programmatic, I firmly believe this approach can help clarify 
the nature of word meaning and compositionality in natural language, and at the same 
time bring us closer to understanding the creative use of word senses. 
Acknowledgments 
I would like to thank the following for 
comments on earlier drafts of this paper: 
Peter Anick, Sabine Bergler, Bran Boguraev, 
Ted Briscoe, Noam Chomsky, Bob Ingria, 
George Miller, Sergei Nirenburg, and Rich 
Thomason. 
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