In historical linguistics, Bartsch's law or the Bartsch effect (French : loi de Bartsch, pronounced [lwadəbaʁtʃ] or effet de Bartsch) is the name of a sound change that took place in the early history of the langues d'oïl (c. 5th–6th centuries AD), for example in the development of Old French.
Bartsch's law was a phonetic change affecting the open central vowel [a] in northern Gallo-Romance dialects in the 5th-6th century. This vowel, inherited from Vulgar Latin, underwent fronting and closure in stressed open syllables when preceded by a palatal or palatalized consonant. The result of this process in Old French was the diphthong [ie]:
Note that [ie] is also the outcome of the diphthongization of [ɛ] in stressed, open syllables:
The chronology of Bartsch's law relative to the more general diphthongization of [a] to [aɛ] (responsible, for example, for the final vowels in mare > mer "sea" or portāre > porter "carry") has not been conclusively established. [1] According to one view, diphthongization took place first, and Bartsch's law is seen as a further segmentation of the diphthong [aɛ] caused by the preceding palatal/palatalized consonant, followed by simplification of the resulting triphthong:
According to a second view, Bartsch's law affected the simple vowel [a], causing it to change to [e], which then diphthongized to [ie]:
Support for the second hypothesis comes the fact that palatal consonants triggered the same change [a] > [e] in unstressed word-initial syllables: [2]
Subsequent changes have obscured the effects of Bartsch's law in modern French. The accent shifted to the second element of the diphthong [ie], and the first element underwent glide formation:
The glide [j] was then lost in most words, either absorbed by the preceding palatal consonant, or eliminated by analogical pressure (e.g. in many verbs of the -er conjugation): [3]
The glide was only retained if subsequent nasalization took place, as in Modern French chien[ʃjɛ̃] "dog" (not *chen*[ʃɛ̃] or *[ʃɑ̃]). [4] Compare with the walloon tchén*[tʃɛ̃]
Consequently, the vowel "e" in these words, which is due to Bartsch's law, is now indistinguishable from the "e" that resulted from the general diphthongization of [a] (as in the words mer "sea", porter "carry", mentioned above). The diphthong [ie] is still visible in the spelling of words like chien "dog" (< canem) and moitié "half" (< Proto-Western Romance [mejˈtade] < Latin medietātem).