Understanding Negation in Positive Terms Using Syntactic Dependencies

Proceedings of the 2016 Conference on Empirical Methods in Natural Language Processing, pages 1108–1118, Austin, Texas, November 1-5, 2016. c⃝2016 Association for Computational Linguistics Understanding Negation in Positive Terms Using Syntactic Dependencies Zahra Sarabi and Eduardo Blanco Human Intelligence and Language Technologies Lab University of North Texas Denton, TX, 76203 zahrasarabi@my.unt.edu, eduardo.blanco@unt.edu Abstract This paper presents a two-step procedure to extract positive meaning from verbal negation. We first generate potential positive interpre- tations manipulating syntactic dependencies. Then, we score them according to their like- lihood. Manual annotations show that posi- tive interpretations are ubiquitous and intuitive to humans. Experimental results show that dependencies are better suited than semantic roles for this task, and automation is possible. 1 Introduction Negation is a complex phenomenon present in all human languages, allowing for the uniquely human capacities of denial, contradiction, misrepresenta- tion, lying, and irony (Horn and Wansing, 2015). Despite negation always being marked—in the ab- sence of a negation cue, statements are positive— acquiring and understanding sentences that contain negation is more challenging than those that do not. Children acquire negation after learning to commu- nicate (Nordmeyer and Frank, 2013), and adults take longer to process negated statements than positive ones (Clark and Chase, 1972). In any given language, humans communicate in positive terms most of the time, and use negation to express something unusual or an exception (Horn, 1989). Albeit most sentences are affirmative, nega- tion is ubiquitous (Morante and Sporleder, 2012): In scientific papers, 13.76% of statements contain a negation (Szarvas et al., 2008); in product reviews, 19% (Councill et al., 2010); and in Conan Doyle sto- ries, 22.23% (Morante and Daelemans, 2012). In OntoNotes (Hovy et al., 2006), 10.15% of state- ments contain a verb negated with not, n’t or never. From a theoretical point of view, it is accepted that negation conveys positive meaning (Rooth, 1992; Huddleston and Pullum, 2002). For example, when reading (1) John didn’t order the right parts, hu- mans intuitively understand that (1a) John ordered something, or more specifically, (1b) John ordered the wrong parts. Interpretation (1a) can be obtained after determining that n’t does not negate verb order, but its THEME, i.e., the right parts. Interpretation (1b) can be obtained after determining that n’t is ac- tually negating right, an adjective modifying parts. Determining which words are intended to be negated—identifying the foci of negation, thereby revealing positive interpretations—is challenging. First, as exemplified in (1a, 1b), there is a granu- larity continuum yielding interpretations that entail each other, e.g., (1b) entails (1a). Second, a single negation often yields several positive interpretations, e.g., from (2) John doesn’t eat meat, we can extract that (2a) John eats something other than meat and (2b) Some people eat meat, but not John. This paper presents a methodology to extract pos- itive interpretations from verbal negation. The main contributions are: (1) deterministic procedure to generate potential interpretations by manipulating syntactic dependencies; (2) analysis showing that dependencies yield finer-grained interpretations and better results than previous work using semantic roles; …

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