Modality and Negation: An Introduction to the Special Issue

Abstract

Traditionally, most research in NLP has focused on propositional aspects of meaning. However, to truly understand language, extra-propositional aspects are equally important. Modality and negation typically contribute a lot to these extra-propositional meaning aspects. While modality and negation have often been neglected by mainstream computational linguistics, interest has grown in recent years, as evidenced by several annotation projects dedicated to these phenomena. Researchers have started to work on modelling factuality, belief and certainty, detecting speculative sentences and hedging, identifying contradictions, and determining the scope of expressions of modality and negation. In this article, we will provide an overview of how modality and negation have been modelled in computational linguistics. Volume ?, Number ? tational treatment of propositional aspects of meaning, like semantic role labeling, and a response to the need for processing extra-propositional aspects of meaning as a further step towards text understanding. That there is more to meaning than just propositional content is a long-held view. Prabhakaran et al. (2010) illustrate this statement with the following examples, where the event LAY_OFF(GM, workers) is presented with different extra-propositional meanings:(1) a. GM will lay off workers. b. A spokesman for GM said GM will lay off workers.c. GM may lay off workers.d. The politician claimed that GM will lay off workers. e. Some wish GM would lay of workers.f. Will GM lay off workers? g. Many wonder whether GM will lay off workers.Generally speaking, modality is a grammatical category that allows the expression of aspects related to the attitude of the speaker towards her statements in terms of degree of certainty, reliability, subjectivity, sources of information, and perspective. We understand modality in a broad sense, which involves related concepts like 'subjectivity', 'hedging', 'evidentiality', 'uncertainty', 'committed belief' and 'factuality'. Negation is a grammatical category that allows the changing of the truth value of a proposition. A more detailed definition of these concepts with examples will be presented in Sections 2 and 3. Modality and negation are challenging phenomena not only from a theoretical perspective, but also from a computational point of view. So far two main tasks have been addressed in the computational linguistics community: (i) the detection of various 2Computational Linguistics Just Accepted MS. Morante and SporlederModality and Negation forms of negation and modality and (ii) the resolution of the scope of modality and negation cues. While modality and negation tend to be lexically marked, the class of markers is heterogeneous, especially in the case of modality. Determining whether a sentence is speculative or whether it contains negated concepts cannot be achieved by simple lexical look-up of words potentially indicating modality or negation. Modal verbs like might are prototypical modality markers, but they can be used in multiple senses. Multiwo...

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