Bartsch's law

In historical linguistics, Bartsch's law or the Bartsch effect (loi de Bartsch, 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.

Description
Bartsch's law was a phonetic change affecting the open central vowel 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 :


 * Latin  > Old French laissier  (modern French laisser "let")
 * Latin  > Old French chier  (modern French cher, Walloon tchîr "dear")

Note that is also the outcome of the diphthongization of  in stressed, open syllables:
 * Latin  >  >  > Old French pie  (modern French pied "foot")

The chronology of Bartsch's law relative to the more general diphthongization of to  (responsible, for example, for the final vowels in  > mer "sea" or  > 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 caused by the preceding palatal/palatalized consonant, followed by simplification of the resulting triphthong:
 * IPA: >  >  >  >
 * Romanicist notation: á > áę > íaę > íę > íẹ

According to a second view, Bartsch's law affected the simple vowel, causing it to change to , which then diphthongized to :
 * IPA: >  >
 * Romanicist notation: a > ẹ > íẹ

Support for the second hypothesis comes the fact that palatal consonants triggered the same change >  in unstressed word-initial syllables:
 * Latin  >  > Old French cheval  "horse"

Further development
Subsequent changes have obscured the effects of Bartsch's law in modern French. The accent shifted to the second element of the diphthong, and the first element underwent glide formation:
 * in IPA: >  >
 * in Romanist notation: íẹ > iẹ́ > yẹ

The glide 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):
 * Old French chier >  > modern French cher  "dear"
 * Old French laissier >  > modern French laisser  or  "let"

The glide was only retained if subsequent nasalization took place, as in Modern French chien "dog" (not *chen  or ). Compare with the walloon tchén

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 (as in the words mer "sea", porter "carry", mentioned above). The diphthong is still visible in the spelling of words like chien "dog" (< ) and moitié "half" (< Proto-Western Romance  < Latin ).