From cantare to chanter

A hypothesis on the palatalization in Old French inferred from the phonetic variation in the Modern German dialects

The transition of the /k/ sound in medieval colloquial Latin (also known as Vulgar Latin) into /s/, /ʃ/, and /tʃ/ in French and Italian is a well-known fact, but how exactly did it happen?

This transition is seen, for instance, in centum > cent, cantare > chanter in French, 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.

One of the curious parts of these chains is /kʲ/ > /tʲ/. If there is nothing in between, it suggests that at some point in time speakers of Vulgar Latin regarded /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 that would only take place in certain phonetic environments.

On the other hand, the example of phonetic variation in the Modern German dialects seems to offer 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. With all of these variants still observed in the living language varieties, this can provide a credible insight to the possible transformations of the /k/ sound.

Since similar phonetic patterns often recur across different language groups, the sound change from Vulgar Latin /k/ to 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, which 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 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 a possible transformation path from Vulgar Latin to 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 survived in English borrowings like chair and chamber.

(3) The sound change /k/ > /ts/ occurring in other languages could have resulted from a further development of /tɕ/ in the same sound chain.