Speech and sign: the whole human language

After more than sixty years of research, it is now widely accepted that sign languages are real languages, sharing key properties with spoken languages. This means that spoken and signed languages together comprise one natural language system in some sense. But that is not the whole story. Here I probe more deeply into the two systems, and focus on the differences between them -- differences that are pervasive, systematic, and predictable. Taking the existence of two identical articulators in sign languages, the two hands, as a case in point, I show how the physical channel of transmission profoundly influences linguistic structure. Further support for the characterization of language proposed here, different systems in the same faculty, comes from the newly emerging sign language of the Al-Sayyid Bedouins. The Whole Human Language can only be fully understood by admitting and elaborating two types of language in one language faculty, and by acknowledging the fundamental role of the body in determining language form.