Morphological vs. Lexical Antonyms in Italian: a Computational Study on Lexical Competition
Authors: Martina Saccomando, Andrea Zaninello, Francesca Masini (Università di Bologna, Fondazione Bruno Kessler, Libera Università di Bolzano, 2024)
Topic: Lexical and Semantic Resources and Analysis

Abstract
In this paper, we examine the competition between pairs of adjectives in Italian that are antonyms of the same term: one is a ``morphological antonym'' formed by negative prefixation, the other is a ``lexical antonym'' with no morphological relationship with the term in question. We consider pairs of adjectives that are reported as antonyms in lexicographic resources and extract the nouns that can be modified by both adjectives from a large corpus. We select a set of 8 nouns for each pair that present higher, lower, and comparable frequencies combined with each antonym respectively and then we perform two experiments with a LLM. Firstly, we perform experiments for masked-token prediction of the adjective, to study the correlation between prediction accuracy and the frequency of the noun-antonym pair. Secondly, we perform a polarity-flip experiment with a multilingual LLM, asking to change the adjective into its positive counterpart, and study the cases where the antonym is changed to the morphological antonym's lexical base, under the hypothesis that a flip to the lexical base indicates a narrower set of senses of the antonymic counterpart.

Introduction
Antonymy is the semantic relationship between terms with opposite meanings. In their canonical form, two antonyms' meanings can be represented as the poles of a semantic continuum where one term has a ``positive" semantic value, the other a ``negative" one AUTHOR. Italian, given a word (e.g., the adjective felice `happy'), antonyms can either be realized via prefixation of that word (e.g. infelice `unhappy') or through an independent lexeme (e.g. triste `sad'). In our work, we refer to these types of antonyms as morphological antonym and lexical antonym, respectively. A word in the lexicon may have both a morphological and a lexical antonym, only one of them, or neither. In this paper, we are interested in triplets of adjectives where a positive adjective (e.g. felice) presents two possible antonyms (or ``co-antonyms''), one formed morphologically by prefixation (e.g. infelice), one morphologically independent (e.g. triste). In this paper, we are interested in studying the factors that govern the selection of the morphological antonym vs. the lexical one. These two types of antonyms express ``negative" semantics with respect to the opposite, ``positive'' term in different ways: implicitly in the case of lexical antonyms; explicitly in the case of morphological antonyms, by adding a prefix with a negative, contradicting value. Because of their different morphological structure, one possible hypothesis on their lexical competition is that the morphological antonym should have a more restricted semantics, representing the negation of the semantics of its adjectival base, while the lexical antonym should have a broader semantic coverage, as it is morphologically independent from its positive counterpart. To the best of our knowledge, there is no empirical study, especially on Italian, that investigates the competition between morphological and lexical antonyms in single languages. Studies on antonyms do identify the two types of antonyms but generally do not address the factors influencing the preference for one type over the other intralinguistically. This study investigates the competition between these two types of antonyms by firstly studying their distribution in corpora (Section 5.1); secondly, testing the ability of a native-Italian language model to predict them in a masked-token prediction task (Section 5.2); and, finally, performing a substitutability task within the same context by switching the polarity of the context sentence with a SOTA multilingual LLM, in order to study when the adjective is switched to the positive un-prefixed adjective or to another, positive but morphologically unrelated one (Section 5.3).

Conclusion
In our study, we aimed to highlight the differences between the two types of antonyms, morphological and lexical, focusing on a computational account of their context of use. While a lexical analysis did not prove decisive, experiments on masked-token prediction and polarity flip, aimed at approximating their semantic coverage, indicate that, unlike often held in current studies, the lexical antonym seems to posses a narrower lexical coverage and scope, supporting the view (such as AUTHOR's and others') that it is indeed the morphological antonym, despite its apparent closer relationship with its lexical base, that possesses the higher degree of semantic generality. This study has an exploratory nature, as previously mentioned, due to the lack of specific research on the subject. For this reason, a limited number of adjectives were selected, exclusively belonging to the core vocabulary. Additionally, the study focused on the Italian language, not only due to the absence of recent in-depth studies on this language but also because of the general decline in linguistic research on Italian. The results obtained contradicted our initial hypothesis. In the future, these results could be confirmed or entirely overturned if a larger data set were considered. furthermore, it would be interesting to investigate whether the results obtained for Italian are also found in languages with morphology different from that of Italian. In a broader framework of expanding the analysis, it would be interesting to focus on additional linguistic factors that determine the choice of a lexical antonym rather than a morphological one, such as semantic networks or word frequency.