Back again to the future: How to account for directionality in grammatical change?

Grammaticalization is commonly understood as a regular and essentially directional process. This generalization appears to be agreed upon in some form or other across many different schools of linguistics, even if it has not gone unchallenged. But there are different views on what exactly is regular. Taking the development from movement-based verbs to future tenses as an example, the present paper argues that neither contextual features nor inferential mechanisms, analogy, or constructional form seem to provide a sufficient basis for explaining the evolution of grammatical categories. The paper is based on the one hand on findings made in ⁠ǃ⁠Xun, a Southwest African language of the Kx’a family, formerly classified as “Northern Khoisan”, and on the other hand on a comparison of this language with observations made in the Germanic languages English, Dutch, and Swedish.