In historical linguistics, Bartsch's law or the Bartsch effect (French: loi de Bartsch, pronounced [lwa d? ba?t?] 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 [?] in stressed, open syllables:
The chronology of Bartsch's law relative to the more general diphthongization of [a] to [a?] (responsible, for example, for the final vowels in mare > mer "sea" or port?re > porter "carry") has not been conclusively established. According to one view, diphthongization took place first, and Bartsch's law is seen as a further segmentation of the diphthong [a?] 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:
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):
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 [mej'tate] < Latin mediet?tem).