Modeling Maltese Noun Plural Classes without Morphemes

Abstract

Word and Paradigm morphology proposes that morphologically complex words are stored as wholes in the mental lexicon, and by doing so it avoids problems that are related to the notion of the morpheme. However, it is not yet clear to what degree it is possible to computationally model classification and production of complex word forms without morphemes.We take up this question by modeling the classification and production of the Maltese noun plural system. Maltese is a Semitic language that has two broad classes of plurals: concatenative ones and non-concatenative ones. We model the classification in two models, and the production in a third one. The first model for classification, the Tilburg Memory Based Learner (TiMBL), is a computational implementation of exemplar models. TiMBL is impartial as to the existence of morphemes in the mental lexicon, and allows us to directly compare the classification with and without morphemes. It turns out that the classification with and without morphemes of Maltese nouns is equally good. The second classification model is the Naive Discriminative Learner (NDL). NDL is a computational implementation of discriminative learning. It can be understood as an implementation of the Word and Paradigm model and thus eschews morphemes. It differs from TiMBL in its assumptions about learning, and they way in which the classifications are obtained. NDL, too, classifies Maltese nouns well. A classification task is very different from a production task, and therefore we used neural networks to model the production of plurals. In these models we address the question whether the production of a plural noun for a given singular can be modeled without recourse to morphemes. We used two neural networks architectures (LSTM and GRU) that have been applied to linguistic phenomena, and find that they are able to correctly produce plurals, without making use of morphemes.We conclude that the Maltese noun plural system can be modeled on the basis of whole words alone without morphemes. These results, therefore, support the Word and Paradigm theory of the mental lexicon.