Defining Action Types: on the roles of Thematic Structures and Argument Alternations
Authors: Massimo Moneglia, Alessandro Panunzi, Rossella Varvara (Università di Firenze, 2019)
Topic: Lexical and Semantic Resources and Analysis

Abstract
The paper focuses on the relation between Action Types (ontological objects that identifies the referential potential of a verb) and the Thematic Structure and Alternations of verbs. The empirical analysis shows that these linguistic features are not properties of the verb itself, but vary in relation to its referential variation. Given this evidence, we argue that Thematic Structure and Argument Alternation can help in the identification of the different types of action to which a verb refers, providing evidences to define the granularity of action concepts in the development of an ontology of actions.

Introduction
Action verbs are among the most frequent words in ordinary communication, and their correct processing constitutes an underpinning element for a wide series of human-machine interaction tasks. The formalization of action verb meanings has often been linked to propositional representations within decompositional approaches (Dowty, 1979; Rappaport Hovav and Levin, 2012), in which the semantic core of the verb remains a non-analyzed lexical root. Other traditional components used in the representation and annotation of the meaning of action verbs are: the temporal and aspectual properties of verbs (Vendler, 1957; Pustejovsky, 1991); the thematic roles of participants (Fillmore, 1967; Gruber, 1965); the force dynamics and causal relations implied (Talmy, 1988; Croft, 2012; Gärdenfors, 2014). Nevertheless, even if these semantic components are usually assumed to reflect the general structure of action conceptualization, the linguistic and the cognitive levels of categorization are not equivalent and should not be confused (Croft, 2012; Moneglia, 2014). As a matter of fact, the lexical category instantiated by an action verb can refer to more than one cognitive entity. For instance, the verb to push can refer to actions in which the force causes the movement of the object in space (e.g. in a sentence like John pushes the basket under the table), as well as to actions in which the object does not move (e.g. John pushes the fabric into a ball). This differential property is more than enough to cognitively distinguish these events in different action concepts. As a consequence, the need for a cognitive level of action categorization which is independent from the lexical one becomes clear. In this paper, we investigate the role of one type of linguistic information, specifically Thematic Structure and Argument Alternations, in the definition of action types, i.e. types of action concepts that gather together single datapoint in the IMAGACT ontology of actions. We point out that Thematic Structure is not a property of the verb itself, since different structures may be present for the same verb. Our aim is to show how these features are linked to action types and how this correlation can be useful for the definition and the induction of Action Types1 . In section 2, we show the innovative methodology assumed by the IMAGACT Ontology of Action for representing the meaning of action verbs, focusing on their referential properties rather than on their intensional definition. In sections 3 and 4, we will see through a case study that the induction of the referential variation of verbs can take advantage of linguistic features. Thematic Structures and their Alternations can have an impact in the definition and characterization of the objects in an ontology of actions.

Conclusion
In this paper we have investigated the relation between Thematic Structure and Action Types. The empirical analysis reveals that Thematic Structure and Argument Alternations are not properties of the whole verb, but rather of the verb in its Types. We have provided evidence about the saliency of both Thematic Structure and Argument Alternations in the identification of Action Types. Although TS and AA do not determine the variation of a verb across different ATs, these linguistic features can, indeed, reveal characterizing features of a Type, helping us in the disambiguation of concepts and in the recognition of the necessary level of granularity in building our ontologies.