The licensing of null arguments in American Sign Language

The distribution of null arguments across languages has been accounted for in terms of two distinct strategies: licensing by agreement and licensing by topic. Lillo-Martin (1986, 1991) claims that American Sign Language (ASL) exploits both strategies for licensing null arguments, depending on the morphological characteristics of the verb. Here we show that this is incorrect. Once the nonmanual correlates of agreement features (comparable to the nonmanual expressions of other syntactic features) in ASL are recognized, it becomes apparent that null arguments in this language are systematically licensed by an expression of syntactic agreement.