A Frame-Based Model of Inherent Polysemy, Copredication and Argument Coercion (2022)

Abstract: The paper presents a frame-based model of inherently polysemous nouns (such as ‘book’, which denotes both a physical object and an informational content) in which the meaning facets are directly accessible via attributes and which also takes into account the semantic relations between the facets. Predication over meaning facets (as in ‘memorize the book’) is then modeled as targeting the value of the corresponding facet attribute while coercion (as in ‘finish the book’) is modeled via specific patterns that enrich the predication. We use a compositional framework whose basic components are lexicalized syntactic trees paired with semantic frames and in which frame unification is triggered by tree composition. The approach is applied to a variety of combinations of predications over meaning facets and coercions.

## introduction the lexical representation of inherently polysemous nouns and the variable evocation of their meaning facets by the predications in which they occur continue to be topics of ongoing research. two questions are of particular interest in this context: (i) what are the mechanisms that underlie copredication constructions in which two or more predicates that aim at different meaning facets are applied to the same nominal argument? (ii) how does facet selection for inherently polysemous nouns differ from cases of argument coercion in which an apparent mismatch between the semantic type of an argument expression and the requirements of the predicate is resolved by an extended mode of composition that draws on additional pieces of lexical or contextual information? examples of inherent polysemy classes are given by nouns such as 'book' and 'letter', which have a physical facet and an information facet, and by nouns such as 'documentation' and 'classification', which have a process and a result facet. the sentence in (1a) illustrates a verb-verb copredication construction in which 'memorize' addresses the information facet of the letter while 'burn' targets its physical facet. in verb-adjective copredication constructions like (1b), it is the argument-taking verb and the modifying adjective that address different facets of the noun. the example in (1c), by contrast, would count as a case of coercion if we assume that poems do not inherently come with physical facets. the examples in (2), retrieved via sketch engine's interface to the acl anthology reference corpus @xcite , show an analogous pattern with respect to the evocation of process and result facets. in (2a), 'conducted' addresses the process facets of the classifications while 'evaluated' (most probably) refers to their result facets. likewise, the modifying adjective 'correct' targets the result facet in (2b). a more systematic approach to distinguishing coercion from polysemy would draw on empirical data from corpus studies and psycholinguistic experiments. as to the former type of approach, @xcite argue that inherent polysemy can be distinguished from coercion by looking at the variability of the co-occuring predicates in copredication constructions, where high variability is taken as an indicator of polysemy. from a psycholinguistic point of view, the hypothesis is that complement coercion comes with higher processing costs @xcite than just selecting a lexically provided facet of a polysemous noun. (see @xcite for a more recent overview of the relevant experiments.) the primary goal of the present paper is not so much to provide a strong empirical basis for the distinction in question but to introduce a formal cognitive model that allows us to represent the postulated semantic differences in a sufficiently finegrained way. a good part of the more recent formal modeling approaches for inherent polysemy and coercion rely on some sort of advanced type-theoretical framework such as type composition logic @xcite , type theory with records @xcite , montagovian generative lexical theory @xcite , unifying theory of dependent types @xcite , and dependent type semantics @xcite . most if not all of them were at least partly driven by the aim to overcome what was seen as formal limitations of @xcite 's original proposal. notably asher (2011, p. 87) regards the typed feature structure formalism used by pustejovsky and feature structure unification as inadequate for modeling copredication and coercion. in this paper, we present a frame-semantic model of inherent polysemy and argument coercion. a central assumption of frame semantics is that attributes (features) play a crucial role for the structured representation of meaning @xcite . our approach builds on the framework of @xcite , where (i) frames are defined as generalized typed feature structures, (ii) semantic frames are linked with syntactic trees, and (iii) frame unification is guided by syntactic tree operations; cf. section 2 for details. @xcite describe a first application of this framework to the analysis of polysemy and coercion. they pursue an "eliminative" strategy with respect to complex types and objects in that they avoid positing special "dot objects" that jointly represent the different meaning facets of an inherently polysemous noun. their idea is that a framebased representation of the facets and the semantic relations between them is sufficient for explaining the flexible behavior of polysemous nouns. for instance, they do not introduce a "dot type" physicalobject • information (phys-obj • info, for short) for characterizing the class of polysemous nouns comprising 'book', 'letter', etc. instead, these nouns are lexically classified as denoting entities of type info(rmation)-carrier, which is introduced as a subtype of phys-obj together with the constraint that its instances have an attribute cont(ent) whose value is of type info. more succinctly, in the formal frame description language used in the present paper: info-carrier ⇛ phys-obj ∧ cont : info. babonnaud et al.'s eliminative strategy has the following two issues: (i) it is usually necessary to decide on a "primary" facet of which the other facet is value of an attribute. (ii) in order to access the "nonprimary" facet of a polysemous noun, the predicate has to anticipate the underlying attribute structure. to give an illustration, consider the two predications 'memorized the letter' and 'burned the letter'. if 'letter' has the type info-carrier then the np 'the letter' is compatible with the selectional restrictions of the patient argument of the verb 'burned', which requires an argument of type phys-obj. figure 1 sketches how argument substitution would lead to the integration of the np argument frame into the verb frame in this case. (the specific choice of the syntactic category labels will be explained in section 2.) combining 'the letter' with 'memorized' by np substitution, on the other hand, calls for more flexible selectional restrictions on the direct object of the verb: the object np can have the type info or the type info-carrier. this is shown in figure 2 where 'memorized' comes with a disjunctive specification: either the direct object is of type info and can directly provide the theme or the theme is the value of the direct object's cont attribute. how- clause core[@xmath0: syntactic and semantic composition for 'burned the letter' (preliminary version) clause core[@xmath1: lexicalized construction for 'memorized' along the lines of babonnaud et al. (2016) a related issue is that babonnaud et al. (2016) employ the same kind of disjunctive encoding for modeling coercion. however, there should be a distinction between coercion mechanisms (linked to the predicate) and accessing different meaning facets (provided by the noun). an example where the difference matters is the selection of the object of 'perform'. assuming that in 'perform an annotation', the frame of 'perform' picks the creation event of the 'annotation' frame, and assuming that such an event is also present in the frame of 'summary', it is not clear why the latter cannot be targeted by 'perform'. the crucial difference is that in "perform an annotation" a meaning facet is targeted ('annotation' is a process • result dot type noun), while "perform a summary" requires a coercion. the unavailability of 'perform a summary' might therefore be due to the absence of an event facet for 'summary' and, furthermore, the unavailability of an adequate coercion pattern for 'perform'. the goal of the present paper is to show how a non-eliminative strategy for modeling polysemous nouns by means of frames can overcome the described issues. to this end, dot types are added as proper members of the type hierarchy. they are not related to their component types by inheritance but rather by functional relations, i.e., by attributes. for example, instances of type physobj • info have two attributes obj(ect)-facet and info(rmation)-facet whose values are of type info-carrier and info, respectively. the two facets are related by the cont attribute as before: figure 3 depicts the two frame representations for the eliminative and the non-eliminative strategy side by side. argument coercion, on the other hand, does not involve facet selection but is analyzed via additional patterns that can be used to augment the semantics of a predicate. ## background: syntax-driven frame composition the formalization of frame semantics used in the present paper is a slightly modified version of the one proposed by @xcite . frames are understood as generalized feature structures. instead of requiring a distinguished root node from which every other node is accessible via a finite attribute sequence, the generalized version allows for multiple labeled nodes under the condition that each node is accessible from at least one of the labeled nodes. correspondingly, frame unification does not require the identification of designated root nodes but relies on the identification of nodes with the same label. frames can be defined as minimal models of conjunctive attribute-value formulas. the underlying logic is described in appendix a. @xcite combine frame semantics with tree adjoining grammars (tag). the basic components of this approach are elementary constructions, which are pairs of elementary syntactic trees and semantic frames where (some of) the constituent nodes of the tree are linked to nodes of the frame. the link is encoded by an i(ndex) constraints for dot types and their meaning facets: constraints for single types and their meaning facets: specification of attributes depending on types: the syntactic side of the approach is not restricted to tag but generalizes to other tree rewriting formalisms. in this paper, we use the formalism of tree wrapping grammars (twg) together with grammatical concepts of role and reference grammar (rrg; @xcite , for which twg has been developed @xcite . rrg provides an elaborate theory of clause linkage, which comes in handy for the analysis of copredication constructions, among others. instead of an x-bar scheme, rrg assumes a layered structure consisting of nucleus, core and clause. the nucleus contains the main predicate, the core contains the nucleus and the (non-extracted) syntactic arguments, and the clause includes the core and extracted arguments. each layer can have a periphery of adjuncts. grammatical operators, that is, closed-class elements encoding tense, modality, aspect, etc., attach to different layers depending on their scope. concerning complex constructions, rrg draws not only a distinction between coordination and subordination but assumes in addition cosubordination constructions, which are dependent but non-embedded structures of the general form in such constructions, operators that apply to category x are usually realized only once but have scope over both x-daughters. the tree composition operations of twg are (simple) substitution (replacing a non-terminal leaf by a tree, as in figure 1 ), sister adjunction (adding a tree as a subtree of a non-leaf, see the adjunction of 'and' in figure 9 ) and wrapping substitution (splitting the new tree at a dominance-edge, filling a substitution node with the lower part and adding the upper part to the root of the target tree, cf. figure 9 ). ## predications over meaning facets in this section, we develop an analysis of predications that target existing meaning facets (either of dot type nouns or of single type nouns). universal constraints. as already mentioned, we introduce attributes for meaning facets and specific types for dot types. meaning facets occur systematically for certain types, and they are therefore introduced by universal attribute-value constraints of the form φ ⇛ ψ. (cf. the appendix for the formal background). some of the relevant constraints for dot types phys-obj • info and process • result are given in figure 4 . they specify available meaning facets together with the specific relations that hold between the different facets: for phys-obj • info, the cont value of the obj-facet is the info-facet, while for process • result, the creation value of the obj-facet is the event-facet and the result of the event-facet is the obj-facet. for sinclause core[@xmath2 figure 6 : revised syntactic and semantic composition for 'burned the letter' (cf. figure 1 ) gle types, the frame node is its own corresponding meaning facet (with self denoting the identity function properly restricted). the third group of constraints specifies subtype relations, for instance every entity of type book is also of type physobj • info, and the last two groups detail incompatibilities between types (e.g., nothing can be of types event and phys-obj at the same time) and between types and attributes (e.g., nothing can be of type phys-obj while having an event-facet). figure 5 shows the application of these constraints to the lexical frame of 'letter'. ## coercion we now extend our analysis to cases of coercion as in (1c) ('burn the poem') and (2c) ('automatic summary'). the examples in (7) show that for the same predicate, depending on the context, different additional frame fragments are coerced, even for the same object nouns. frame for 'summary': revised frame for 'automatic' (tree as in figure 8 ): (7) a. […] mr. darcy had much better finish his letter. foot_7 b. let us start by discussing 'automatic summary'. if the modified noun has an event facet, we can apply 'automatic' directly. otherwise, we have to coerce an event. this could simply be done by adding an attribute event-facet on the fly via unification. but this would predict that we target always the same event, which is not the case. the event facet (if existent) is unique, but not the coerced events. for example, let us assume that kim has to grade a number of manually and automatically produced summaries. in this situation, 'finished' in sentence (8) may refer to the process of grading the summary while 'automatic' refers to creating it. in 'automatic summary', the noun does not have an event facet, while the adjective adds a manner specification to a process, in this case to the creation of the summary, which is part of the frame of 'summary' (see figure 11 ). 10 this type of coercion, namely targeting the creation event, is common among manner adjectives, so we assume that there is a coercion pattern for this, that can be applied to manner modifications in general. coercion clause core[@xmath3 figure 12 : tree-frame pair for 'finished' patterns are defined as separate classes in the metagrammar (a factorized description of elementary tree frame pairs) and then combined in a disjunction with the basic pattern. since coercion patterns are metagrammar classes, they can be (re)used in different constructions. figure 11 shows the resulting disjunction of frames for 'automatic'. the first frame is used when combining with a noun that has an event facet, while the second is used when combining with a noun that has a creation attribute. (note that, technically, this disjunction is part of the metagrammar and will therefore already be compiled out when computing the elementary constructions.) the composition of 'automatic summary' (x . = y in figure 11 ) necessarily chooses the coercion option, since a summary cannot have an event facet. coercion can easily be combined with predications over existing meaning facets, as in 'evaluate the automatic summary' since the meaning facets of the noun are not changed by the coercion patterns. as we have seen, 'automatic' in 'automatic summary' follows an existing path in the noun frame in order to retrieve its argument. this is different for 'finish' in (7). when triggering a coercion, 'finish' creates a new event frame (the coerced event) which embeds the denotation of the noun as a participant, more concretely as an undergoer. this is expressed in the frame in figure 12 where the disjunction contains the basic pattern (the theme 2 is the existing event-facet) and a coercion pattern ( 2 is a newly created event). an aspect that is missing here is that the coerced event tends to be of a type that corresponds to the telic qualia of the noun (e.g., writing in (7a); cf. pustejovsky 1995). one could model this within frames by including frame types as proper frame objects. we leave this for future research. with this analysis, we can apply more than one coercion leading to different coerced frame elements of the same type, as in (8). and we can also apply coercion to dot type nouns, creating new frame nodes in addition to the available facets, even when one of the facets matches the type requirements. for example, if we replace 'summary' in (8) by 'annotation' then 'automatic' refers to the event facet of 'annotation'. in this case, the basic pattern as well as the coercion pattern are possible. ## conclusion in this paper, we proposed a frame-based analysis of dot objects, predications over their meaning facets, and, in contrast to this, coercion. a crucial aspect of our analysis is that the meaning facets are modeled as attributes in the lexical frames of dot type nouns, while coercion involves the application of coercion patterns that are defined in the metagrammar. their application is constrained by lexical properties, but the meaning components added by coercion are not part of the lexical entries and are in particular not meaning facets. this accounts for the high flexibility of coercion, i.e., the possible variability of the coerced meaning components.