 Special treatise on the phonological consequences of grammaticalization and lexicalization in the Chinese languages can be found in Wei-Heng Chen(2011), which provides evidence that a morphophonological change can later change into a purely phonological change, and evidence that there is a typological difference in the phonetic and phonological consequences of grammaticalization between monosyllabic languages (featuring an obligatory match between syllable and morpheme, with exceptions of either loanwords or derivations like reduplicatives or diminutives, other morphological alternations) vs non-monosyllabic languages (including disyllabic or bisyllabic Austronesian languages, Afro-Asiatic languages featuring a tri-consonantal word root, Indo-European languages without a 100% obligatory match between such a sound unit as syllable and such a meaning unit as morpheme or word, despite an assumed majority of monosyllabic reconstructed word stems/roots in the Proto-Indo-European hypothesis), a difference mostly initiated by the German linguist W. Humboldt, putting Sino-Tibetan languages in a sharp contrast to the other languages in the world in typology.Obligatorification occurs when the use of linguistic structures becomes increasingly more obligatory in the process of grammaticalization.Lehmann describes it as a reduction in transparadigmatic variability, by which he means that "the freedom of the language user with regard to the paradigm as a whole" is reduced.