Lexical Factorization and Syntactic Behavior (2017)

Abstract: In this paper, we examine the correlation between lexical semantics and the syntactic realization of the different components of a word’s meaning in natural language. More specifically, we will explore the effect that lexical factorization in verb semantics has on the suppression or expression of semantic features within the sentence. Factorization was a common analytic tool employed in early generative linguistic approaches to lexical decomposition, and continues to play a role in contemporary semantics, in various guises and modified forms. Building on the unpublished analysis of verbs of seeing in Joshi (1972), we argue here that the significance of lexical factorization is twofold: first, current models of verb meaning owe much of their insight to factor-based theories of meaning; secondly, the factorization properties of a lexical item appear to influence, both directly and indirectly, the possible syntactic expressibility of arguments and adjuncts in sentence composition. We argue that this information can be used to compute what we call the factor expression likelihood (FEL) associated with a verb in a sentence. This is the likelihood that the overt syntactic expression of a factor will cooccur with the verb. This has consequences for the compositional mechanisms responsible for computing the meaning of the sentence, as well as significance in the creation of computational models attempting to capture linguistic behavior over large corpora.

## introduction there is a long and established tradition in linguistics of the application of component-based decomposition for the analysis of lexical meaning. early work in generative grammar incorporated both the feature-based analysis promoted by @xcite and others @xcite , as well as the adoption of more structured lexical templates as put forth by @xcite , @xcite , @xcite , and @xcite , to the study of verb classes and the syntactic and semantic variations associated with class membership. in this paper, we reevaluate the significance of lexical decomposition strategies as they were employed in early generative linguistic studies of verb meaning and syntactic variability, an area now often referred to as the lexicon-syntax interface, and consider their influence on contemporary treatments of argument selection and polysemy. we look at the general strategy of lexical factorization as a method for characterizing variations in meaning within a semantic class, focusing in particular on an unpublished 1972 manuscript of aravind joshi's, "factorization of verbs: an analysis of verbs of seeing". this work adheres to a style of lexical factorization that was common in the 1970s, particularly with linguists exploring the impact of semantic factors on syntactic behavior or psychological plausibility. for example, joshi's analysis follows a scheme introduced by @xcite to analyze the conceptual relations between motion verbs, as a way of modeling lexical memory. miller and other early researchers opened up new avenues for exploring both the psychological and semantic modeling of linguistic representations for lexical forms @xcite , @xcite ). we argue that the factorization methodology, as adopted in joshi's paper and by other earlier generative linguists, is relevant to the current discussion on mapping to syntax from lexical forms for several reasons. first, componential analysis and factorization, as carried out by both @xcite and @xcite -and exemplified in joshi's analysis as presented here-remain important aspects of the analytic toolkit for modeling word meaning in linguistics. in fact, much of the work on semantic type systems and typed feature structures developed in part out of this work. the selectional behavior of predicates, on this view, is a reflection of the types associated with the verb's arguments, and the specificity of an argument's type reflects the meaning of the predicate in a direct manner. we will show how the modern day analyses of polysemy and argument selection in linguistics are related to these earlier models of lexical factorization, illustrating how joshi's lexical decomposition can be re-interpreted in terms of contemporary semantic models. we then explore the relationship between lexical factorization and the expected syntactic expressibility of semantic variables within the sentence. @xcite analysis, along with @xcite work and fillmore's early analyses in terms of case frames @xcite have an additional relevance and topicality for current computational approaches to language modeling and disambiguation. by analyzing lexical forms in terms of a restricted inventory of semantic features, where a given sentential frame has a fixed number of semantic parameters available to it, one is able to identify the possible factors within a sentence as being either lexically encoded or overtly expressed in the syntax. one obvious consequence of this is that a specific lexical factorization for a verb's word sense will influence the syntactic expressibility of these and other factors. such an association is related to the standard information theoretic metrics used in computational models for lexical disambiguation or computing the likelihood of phrasal attachment. in fact, one can define the factor expression likelihood for a verb sense, based on its constituent semantic factors. this is the likelihood that the overt syntactic expression of a factor will cooccur with the verb. this has consequences for the compositional mechanisms responsible for computing the meaning of the sentence, as well as computational significance in the creation of language models attempting to capture linguistic behavior over large datasets. this work can be seen as a logical extension of the work begun in @xcite , @xcite , exploring the link between theory and distributional properties of linguistic data. ## factorization of lexical meaning before we explore the factorization model from @xcite in detail, it is worth briefly reviewing the basic motivation behind theories of lexical decomposition within linguistics. one of the major concerns in both early generative and non-generative (distributional) linguistic research was the question of how verb meanings relate to various syntactic forms within the sentence; that is, linking lexical-semantic forms to syntax @xcite . because of the general assumption within generative semantics that the deep structure of a sentence completely determined its meaning, the structure of lexical representation was an important research concern. transformations could add, delete, or edit structures, but not change the semantic content conveyed by the resulting expression, i.e., the surface structure. 1 hence, the proper lexical encoding of semantic features was of critical concern @xcite . 2 the features comprising the di↵erent aspects of semantics for lexical items were thought of as components, primitives, or factors, of meaning @xcite . from work in generative semantics @xcite , through case grammar @xcite early interpretive semantics @xcite ) some common themes emerge concerning the decompositional aspects of word meaning. we will focus on verb meaning, since the subject of joshi's article is on a subclass of perception predicates, the verbs of seeing. the list below is not exhaustive, but does cover many of the factors contributing to the meaning of a predicate: most of these have been considered as component factors in decompositional models within linguistics by dowty, lako↵, jackendo↵ to name just a few. but how are these factors encoded in the representation of lexical meaning? for the purpose of discussion, we will abstract away from the di↵erences between lexical semantic models, in order to better appreciate the role factorization has played in the development of current theories of semantic selection. in order to formally distinguish the various techniques of decomposition, we first identify a predicate expression as being composed of both a argument list and a body. this is schematically illustrated in (2) below. 3 (2) args x i body @xcite syntactic forms made many of these forms of lexical substitution models di cult to maintain. we can think of body as denoting the content of a predicative term, regardless of its form or complexity. likewise, args denotes the list of parameters that participate in the expression within the body. by examining how this simple predicative template is modified, we can identify four di↵erent strategies for defining the semantics of a predicate. these are listed in (3) below, where we illustrate the di↵erences in how verb meanings are defined. the verb meaning is represented as a primitive (predicative constant) in the semantics, p, but additional parameters, p i , are added for interpretation in the model, that are not overtly realized in the syntax. the verb meaning is represented by a complex expression of subpredicates, p 1 , . . . p k , while also adding additional parameters, binding into the subpredicates (where x i and x j are instances of x, and p k and p l are instances of p): early approaches to modeling language meaning with formal logic, such as @xcite , as well as fodor's more recent position @xcite , are non-decompositional, and can be identified with the atomic predication approach in (3a). on this view, if inferences are to be made between members of a language's lexis, then they are accomplished by meaning postulates or explicit axioms. hence, related meanings of a word are encoded as separate lexical entries; for verbs, even variations in subcategorization frames must be encoded as distinct entries. consider the impact this approach has for the interpretation of a verb's meaning, for example, the perception verb, see. assuming the basic veridicality of perception reports (cf. @xcite , we can infer the factivity of what we see. 4 hence, from (4a) we can infer (4b). further, from our understanding of vision as a kind of perception, we can also infer (4c) from ( 4a ). these inferences are not part of the verb's meaning, but rather are accomplished with the help of rules or axioms that accompany the atomic meaning of lexical items. now consider the same verb analyzed in terms of lexical factors, following the strategy of structured factorization, described in (3d). 5 one of the motivations for structured predicative decomposition is the ability to read inferences such as those above directly from the semantic form of the sentence. that is, by decomposing see in ( 5 ) below, into the three lexical factors sight, perceive, and by-means, the inferences in ( 4b ) and (4c) are directly recoverable (where y is typically typed as thing or event, as in (4a)). in the discussion below, we argue that the tradition of structured factorization opened new avenues for studying semantic associations within the lexicon, and paved the way for systematic models of argument selection. in the next section, however, we first review the contents of joshi's 1972 manuscript, "factorization of verbs: an analysis of verbs of seeing", and examine how factors are deployed to model verb classes and lexical ambiguity within classes. ## joshi's "verbs of seeing" a major motivation for lexical factorization and decompositional approaches to word meaning was the belief that lexical semantic templates for words largely determine their syntactic behavior in the language. joshi's unpublished article, "factorization of verbs: an analysis of verbs of seeing" (henceforth vos), is a study of how this is realized within the class of visual perception verbs. he gives the criteria for inclusion in this general class as follows: a seeing verb involves visual perception in many di↵erent ways: (a) the subject of the verb sees something or the object of the verb becomes visible (e.g. see: the modulating predicates mentioned above are what we refer to as factors of meaning: decompositional elements similar in some respects to the predicates used in generative semantics @xcite @xcite . the semantic variability within this class is accounted for with combinations of operator-operand expressions, a technique employed with regularity in early generative analyses adopting the strategy used in @xcite , joshi first identifies the core element of meaning that is shared by all verbs in the class of visual perception predicates. this is shown in (6) along with its representation in terms of factors. joshi also follows miller in identifying the most important types of evidence for factorization as: a. syntactic-semantic evidence; b. semantic evidence; and c. psychological evidence. unlike the analyses in generative semantics, however, miller and joshi eschew an interpretation of decomposition as providing a complete determination of the meaning for a lexical item. hence, both the base element of a verb class and the subsequent factorizations of the other verbs are to be taken as incomplete definitions. joshi's paper analyzes around 60 verbs of seeing, given here: appear, flash, scrutinize, behold, flaunt, secrete, blind, gaze, screen, blur, glance, see, conceal, glare, search, cover, glimpse, seek, darken, hide, show, descry, inspect, sight, disclose, look, spot, dazzle, mask, stare, display, notice, surface, disappear, obscure, survey, discern, observe, uncover, emerge, overlook, unmask, espy, peek, vanish, examine, peep, view, expose, peer, watch, exhibit, reappear, witness, eye, regard, fade, resemble, fade-in, reveal, fade-out, scan. there are eleven basic subtypes that are identified within this class, each represented by a unique lexical factorization. further, within each subclass, the various word senses are themselves distinguished by uniquely factorized expressions. there are two immediate consequences of organizing lexical items in this fashion. ## factors and argument selection having reviewed the basic factorization analysis of perception predicates as presented in @xcite , we turn to how aspects of this theory can be viewed within current approaches to argument selection. we will discuss the relation between selection and the elements that are assumed as part of the type inventory of the compositional semantic system. in almost all treatments of lexical decomposition within generative linguistics from the 1960s and 1970s, the arguments to the predicates are taken as variables in a standard first-order domain. hence, any restrictions to the predication are handled as identifiers or classifier predicates. as mentioned above, a richer system of types works to effectively introduce the test of "possible satisfaction" of an argument to a predicate by restricting the kinds of arguments that can combine with a predicate. let us walk through how we can interpret the verb factorizations encountered in the previous section within a richer typing environment. consider the expression for a two-place predicate, p, which consists of the lexical factors p 1 , . . . , p k . the variables are typed as individuals, i.e., e, and the entire expression is therefore a typical first-order relation, typed as @xmath0. how does this correspond to selectional models that assume richer systems of types, such as hpsg, lfg, ccg, or gl? @xcite identified five distinct senses for the verb see. the first three are variants, di↵ering only in the typing restrictions associated with a specific argument (what joshi calls a "classifier" or "identifier" predicate). a richer typing structure for the arguments can identify such predicates in the body of the expression, and restrict the application of the function to arguments satisfying that type. this allows us to express the logical polysemy of the first three senses more clearly, while at the same time, di↵erentiating these from the derived richer senses found in (37d-e). when semantic factors are lexically encoded, they behave in many respects like arguments. they may even license selection. this has been discussed in terms of the di↵erent kinds of arguments that a verb may select. within generative lexicon, for example, there is a distinction made between conventional arguments (obligatory and default) and shadow arguments, those that can appear only if the syntactic realization of the factor provides new information @xcite . for example, consider the phenomenon of incorporation seen in sentence ( 42 ) and ( 43 what these examples illustrate is the relationship between information that has been incorporated into the verb, and how it can be used to license the expression of arguments, under certain conditions. on this analysis, both verbs elbow and butter carry a shadow argument, which can only be overtly expressed if it is "more informative" ( @xcite . how does this relate to the factorization analysis as employed by joshi in the previous section? following the decomposition strategy developed in @xcite , the verb butter can be glossed as follows, where the semantic factor of butter is incorporated into the verb's meaning, building on a base representation of the relation spread. we will adopt the distinction between obligatory (x) and shadow (x s ) arguments introduced above. (45) @xmath1, y, z)] the behavior of the sentences in (43) suggest that lexical factorization can block the syntactic realization of a shadow argument, (43b), unless it is more informative, as in (43c). ## some thoughts on factorization in syntax the relevance of factorization for lexical choice and syntactic realization comes from some obvious properties of how factors encode a word's meaning and how this impacts the subsequent syntactic behavior of the word in a sentential context; that is, there is a correlation between the information encoded in a verb v, and the expression of factors for a particular situational frame in which it is used. it has long been recognized that correlations between lexical items and the properties of selection can be linked to patterns of linguistic behavior in data @xcite , @xcite ), and this discussion relates directly to work done in corpus and distributional linguistics, starting with @xcite , @xcite , up to the present. recall from previous discussion that, within a situational frame, a semantic factor, f i , can be either lexically encoded, syntactically realized, or not expressed at all. in fact, it might be expected that lexical and syntactic factorization is inversely correlated in an utterance: that is, if a verb already incorporates a semantic factor, f i , then it is less likely to be expressed syntactically. likewise, if the verb does not incorporate such a factor, it might be more common to see it appear in the syntax. we refer to this as an informal statement of the factor expression likelihood (fel), which we characterize more formally below. in order to measure the likelihood of a specific semantic factor being expressed syntactically, we need some characterization of the syntactic constructions associated with the factor. let us adopt the following thesis. this is essentially a generalization of semantic mapping strategies that have been proposed since @xcite , mccawley (1968), and @xcite . to illustrate how this works, we see how named semantic relations (e.g., thematic or case roles) can systematically project to syntax. ## conclusion in this brief note, we have attempted to frame the original theoretical questions motivating the @xcite analysis of the verbs of seeing in terms of the current debate concerning the lexicon-syntax interface. we have cast the analysis in terms of recent developments in lexical semantics, and then examined the consequences of this analysis with respect to distributional interpretations of syntactic behavior. we introduced the notion of factor expression likelihood to capture the dependency of a lexical factor on its independent expressibility in the syntax. while the results discussed here are preliminary, they suggest that a purely distributional accounting of the correlation of syntactic behavior with encoded factors must be discarded in favor of a view allowing for a more nuanced theory of semantic selection. these issues are obviously ripe for future investigations, which should cover a much wider range of verbs and their modifiers.