One grammar or two? Sign Languages and the Nature of Human Language

Linguistic research has identified abstract properties that seem to be shared by all languages—such properties may be considered defining characteristics. In recent decades, the recognition that human language is found not only in the spoken modality but also in the form of sign languages has led to a reconsideration of some of these potential linguistic universals. In large part, the linguistic analysis of sign languages has led to the conclusion that universal characteristics of language can be stated at an abstract enough level to include languages in both spoken and signed modalities. For example, languages in both modalities display hierarchical structure at sub-lexical and phrasal level, and recursive rule application. However, this does not mean that modality-based differences between signed and spoken languages are trivial. In this article, we consider several candidate domains for modality effects, in light of the overarching question: are signed and spoken languages subject to the same abstract grammatical constraints, or is a substantially different conception of grammar needed for the sign language case? We look at differences between language types based on the use of space, iconicity, and the possibility for simultaneity in linguistic expression. The inclusion of sign languages does support some broadening of the conception of human language—in ways that are applicable for spoken languages as well. Still, the overall conclusion is that one grammar applies for human language, no matter the modality of expression.