This chapter analyses of null arguments that were initially proposed in the generative tradition for spoken languages. In natural languages, including sign languages, some categories need to be overtly expressed, although they are active both syntactically and semantically. A pretty clear fact is that when an argument is null, there must be some way to identify its semantic contribution to the clause. Two distinct mechanisms have been identified. The first one is morpho-syntactic and can be exemplified by those Romance languages that have a rich paradigm for subject agreement. However, the Italian-type mechanism cannot be the only mechanism that allows null arguments. The reason is that there are other languages, including Chinese, Japanese, and Korean, that allow null arguments, although the verb carry any agreement morphemes. The starting point of their approach is the observation that agreement features in ASL have non-manual correlates that should not be neglected in the analysis of null arguments.