Ad-hoc scalar implicature in adults and children

Ad-hoc scalar implicature in adults and children Alex Stiller Noah D. Goodman Michael C. Frank astiller@stanford.edu Symbolic Systems Program Stanford University ngoodman@stanford.edu Department of Psychology Stanford University mcfrank@stanford.edu Department of Psychology Stanford University Abstract Linguistic communication relies on pragmatic implicatures such as the inference that if “some students passed the test,” not all did. Yet young children perform poorly on tests of implicature, especially scalar implicatures using “some” and “all,” until quite late in development. We investigate the ori- gins of scalar implicature using tasks in which the scale arises from real-world context rather than conventional contrasts be- tween lexical items. Experiment 1 shows that these ad-hoc implicatures are easy for preschool children, suggesting that children have an early competence at pragmatic inference, and that failures in standard scalar implicature tasks are due in- stead to problems contrasting lexical items. Experiments 2 and 3 compare a Gricean, counterfactual account of implica- ture with a linguistic alternatives account and find that neither predicts effects of contextual informativeness. We conclude that an account of pragmatic implicature must integrate world knowledge, linguistic structure, and social reasoning. Keywords: Scalar implicature; pragmatics; language acquisi- tion. Introduction Sometimes the absence of a description says just as much as its presence. A professor who says “some students passed the test” implies that some students failed—if all had passed, a cooperative speaker would have made the stronger statement “all students passed.” Scalar implicature refers to the conver- sational shorthand of using weak terms to imply the negation of stronger ones that lie along the same “scale.” In this pa- per we investigate the origins of scalar implicature, and the nature of scales, by investigating a spectrum of tasks that are logically equivalent to conventional scalar implicature but in which the scale arises (or fails to arise) from the real-world context rather than the lexical items—ad-hoc implicatures. Implicatures surface in a variety of contexts beyond the case of quantifiers, including modal operators such as “might” and “must” (Noveck, 2001), inclusive and exclusive disjunction (Braine & Rumain, 1981), and numerals (Barner & Bachrach, 2010). A wide variety of theoretical frameworks have been proposed to explain implicature, with the two most influential being (1) Gricean approaches that we will collec- tively call the counterfactual theories (Grice, 1975; Levinson, 2000) and (2) views based on grammatically computed lin- guistic alternatives (Fox, 2007; Chierchia, Fox, & Spector, Grice (1975) offers two maxims from which scalar im- plicatures are meant to follow: make your contribution as informative as is required, and do not make your contribu- tion more informative than is required. From these it fol- lows that any alternative statement which is more informative than the spoken statement must be false—because the speaker could have said that statement had it been true. Under this Figure 1: Example stimuli from our ad-hoc scalar implicature task. The utterance “My friend has glasses” receives different interpretations when the context given to the listener is Row 1 versus Row 2. Each has a similar logical structure to the conventional some-not-all implicature (top). analysis, the relevant scale arises from the logical structure of the possible statements that could have, counterfactually, been uttered. Although neo-Gricean accounts have modified some parts of this basic inferential mechanism, the general predictions remain (Levinson, 2000). In response to appar- ent over-prediction of implicatures by the counterfactual the- ory, the linguistic-alternatives theory claims that implicatures arise by a process in which a statement is strengthened by negating the alternative statements—where the alternatives, and hence scales, derive from the lexical and grammatical structure of language; importantly, more complex statements are not taken to be alternatives (Fox, 2007; Chierchia et al., Consider the three situations shown schematically in Fig- ure 1. At the top, the word “all” is logically stronger than the word “some”, though some applies whenever all does. There is thus a natural scale of informativeness set up by the conventional semantic content of the words. In contrast, the feature words “glasses” and “top hat” have no conventional ordering, but in the context of the three faces in the middle row (“scales” condition), top hat is similarly stronger than glasses, though glasses applies to any object that top hat does. If a speaker says “the one with glasses” we may draw the im- plicature that she means the middle face (an intuition which we test in Experiment 1)—the situation itself seems to set up