2018-09 A. Tkačenko
A living hint to palatalization in medieval Latin
The palatalization of the Vulgar Latin sound /k/ into Modern Romance /s/, /ʃ/, and /tʃ/ is an established fact (as in centum > cent, cantare > chanter in French, and centum > cento in Italian), and the generally accepted view of these transformations is the following:
/k/ > /kʲ/ > /tʲ/ > /ts/ > /s/ — in Lat. centum > Fr. cent,
/k/ > /tʃ/ > /ʃ/ — in Lat. centum > It. cento and Lat. cantare > Fr. chanter.
Since phonetic transformations usually progress over time by gradually involving more speakers, at any given time a shift in articulation is only adopted by some speakers, with the rest most likely perceiving it as unquestionably comprehensible. Therefore, a complete sound chain fully representing its natural course should be a sequence of allophones, with any two neighboring sounds in the chain being allophones of the same phoneme.
If the first sound chain above is complete, it implies that at some point in time different speakers of Vulgar Latin treated /kʲ/ and /tʲ/ as close variations of the same sound while speaking to each other. There is not much detail on how this could happen, apart from attributing this change to a shift of the point of articulation which would only take place in certain phonetic environments (see, for instance, Elcock The Romance languages, p. 53).
On the other hand, an example of phonetic variation in the Modern German dialects seems to suggest a different perspective. The sound pronounced as /ç/ in Standard German, as in ich, is rendered as /k/ and /kʲ/ in Low German, /ɕ/ (and in certain conditions /j/) in Kölsch and other Central German dialects. A similar phonetic variation is seen with the adjectival suffix -ig. Since all of these variants are still observed in the living language varieties, this provides a credible insight to the possible transformations of the /k/ sound.
With this in mind, the sound change from Vulgar Latin /k/ to Modern French /ʃ/ could have passed in the following steps:
/k/ > /kʲ/ > /ç/ > /ɕ/ > /ʃ/, as in cantare > chanter.
In this chain, each pair of the neighboring sounds are close allophones that could be taken for a single phoneme by speakers of the language, as proven by modern Germans. The other possibilities of the development of Vulgar Latin /k/ observable in Modern French can also be aligned with this chain:
/k/ > /kʲ/ > /ç/ > /ɕ/ > /sʲ/ > /s/, as in centum > cent,
/k/ > /kʲ/ > /ç/ > /j/ > /∅/, as in facere > faire.
Related phonetic changes
(1) The above chains can also be adjusted to fit Modern Italian:
/k/ > /k/, unchanged as in cantare,
/k/ > /kʲ/ > /ç/ > /ɕ/ > /tɕ/ > /tʃ/, as in centum > cento.
(2) Similarly, a /tɕ/ or /tʃ/ sound could have emerged from /ɕ/ in varieties of Old French, not as a predecessor of /ʃ/, but as a regional alternative. This particular variant could have been borrowed into English (to be nowadays observed in English loanwords like chair or chamber).
(3) The sound change /k/ > /ts/, which does occur in other languages, could have resulted from a further development of /tɕ/ in the same sound chain.