The grammaticalization of headshakes
All sign languages investigated to date make use of a side-to-side headshake in the context of negation. This headshake, however, is qualitatively different from the co-speech gesture used by speakers in similar contexts. Following a discussion of the origin and use of gestural headshakes, we show that across sign languages, the distribution of headshakes – in particular, their scope and co-occurrence with manual negative elements – is subject to language-specific constraints, which are clearly linguistic in nature. We thus argue that the headshake, as used in sign languages, is a linguistic element which has grammaticalized from a gestural input. We further discuss different types of sign language negation systems from a typological perspective, and we provide some speculations on their evolution in terms of Jespersen’s Cycle.