Preliminaries This chapter covers what have traditionally been called grammaticality judgments in linguistics (which are more aptly referred to as acceptability judgments – see below). We examine such judgments from several angles, with the goal of assisting researchers in deciding whether and how to use this kind of data. Our goal in this chapter is to provide an introduction to the major themes that arise when using acceptability judgments as a data source for the construction of linguistic theories. Importantly, this chapter will not be a step-by-step guide for constructing a particular experiment, as the curious reader can find several fine introductions to the mechanics of experiment construction and analysis elsewhere (e.g., Chapters 7 and 8, and Cowart 1997). Instead, we intend this chapter to be an introduction to the theory underlying the methodology of acceptability judgment collection. Most of what follows will involve discussion of syntactic well-formedness judgments, because that is where the greatest amount of research about judgment data has been focused, but we believe that many of our remarks are also relevant for judgments at other levels of linguistic representation. Specific considerations regarding other sorts of judgments can be found elsewhere in this volume. For example, judgments about the lexicon and phonotactic well-formedness are generally gathered in the language documentation process (see Chapter 4); judgments about morphological processes might be gathered using the experimental methods that predominate in psycholinguistics (see Chapter 8); judgments about sociolinguistic variables might be gathered via a survey (see Chapter 6). For considerations specific to semantic judgments, see Matthewson (2004) and Chemla and Spector (2011).

We present new evidence for the view that specific language impairment (SLI) involves a syntactic feature deficit within a nondeviant grammar. The data involve morphological case and its interaction with verbal inflection. Children with SLI (like younger unaffected children) produce certain pronoun forms in contexts that do not exist in adult language, for example, Him run, which we take as important evidence about their grammars. Both unaffected children and those with SLI show a distributional asymmetry in their production of non-nominative versus nominative pronouns as subjects: Nominatives appear abundantly with both uninflected and agreeing verbs, whereas non-nominatives almost never appear with agreeing verbs. This contingency is predicted on the: view that children are conforming to Universal Grammar, extrapolating beyond their input data. The findings are explained by a model in which the syntactic features Agreement and Tense are optionally omitted from the clause structure.