The Joret line (French: ligne Joret) is an isogloss used in the linguistics of the langues d'oïl. Dialects North and West of the line have preserved Vulgar Latin /k/ and /ɡ/ before /a/; dialects South and East of the line have palatalized /k/ and /ɡ/ before /a/. This palatalization gave Old French /tʃ/ and /dʒ/, then modern French /ʃ/ and /ʒ/. The line was first identified by Charles Joret and published in 1883.
To the North and West of the line lie the Picard language and some dialects of the Norman language. To the South and the East lie other Oïl dialects including southern Norman, Walloon and French. The area North and West of the ligne Joret is sometimes called the Normano-Picard domain.
The Joret line extends from the Channel Islands (including Jèrriais, Guernésiais and Sercquiais) and across the continent from Granville, Manche to the linguistic border with the Dutch language in the North of France and Belgium. It runs approximately West to East through Normandy north of Granville and Villedieu-les-Poêles and divides Manche in two linguistically and separates Calvados and Orne along with Eure; then it curves progressively to the North and ends up approximately South to North in Picardy, where the line runs with the Amiénois and Thiérache, up to the west of Rebecq, Beaumont and Chimay in Belgium where it separates Picard from Walloon.
- Norman Picard /k/ ~ Southern Norman, French /ʃ/, Walloon /ʧ/ (palatalization)
- Latin cattu (cat) gave rise to /ka/ cat north of the line and /ʃa/ chat to the south.
- Low Latin *captiare (to catch) gave rise to cachier / cacher (> English catch) north of the line and chasser (> English chase) to the south.
- Low Latin *cantionem (song), Picard canchon West of the line, French chanson, Walloon tchinson South and East of the line. Similarly Latin cantare → canter vs. chanter, tchanter.
- Frankish *pokka (bag) gave rise to /puk/ pouque (> English dial. poke) north of the line and pouche (> English pouch) to the south. French poche (pocket), Norman pouquette (> English pocket).
- Latin candela (candle) gave rise to candelle north of the line and chandelle to the south.
- Celtic *carros > Latin carrus gave rise to car (> English car) north of the line and char (wain, carriage), chariot (> English chariot) to the south.
- Celtic *kagio-, Gaulish caio- > Norman Picard kay, cay (> ME kay) > French quai (> English quay); Old French chay > French chai (wine cellar)
- Norman Picard /ɡ/ ~ Southern Norman, French /ʒ/, Walloon /ʤ/ (palatalization)
- Latin gamba (leg) gave rise to /ɡãb/ gambe north of the line and /ʒãb/ jambe to the south, djambe to the East.
- Frankish *gard- (yard) gave rise to gardin (> English garden) north of the line and jardin to the south.
- Late Latin *galleto > Norman Picard gal(l)on (> English gallon) ; Old French jallon , French jalon (measure)
Another effect of the palatalizations a bit further to the north but quite parallel was this:
- Norman Picard /ʃ/ (or /tʃ/) ~ Southern Norman /ts/ or /s/, French /s/.
- Low Latin *captiare > Norman Picard cacher, cachi(er) (> English catch); Southern Norman, French chasser
- Low Latin ceresiu(m) > Norman Picard cherise, chrise, chise (> English cherry); Southern Norman srise French cerise
A third isogloss, marking a consonantal change unrelated to the others, more or less follows the Joret line throughout Normandy and continues through northeastern France. It includes all of Picardy, Wallonia, Champagne, Lorraine and a part of Burgundy.
Germanic /w/ (sometimes Latin /v/ was affected as well) was kept north of the line (written w or v), but became /g/ (written g or gu) south of the line.
- Northern French /v/ ~ French /g/
- Latin vespa / Frankish *waspa (wasp) > Picard Wespe, Norman Vêpe ~ French guêpe (wasp)
- Frankish *wahla hlaupan (S. English well and leap) > Picard, Old Norman waloper (> English wallop) ; French galoper (> English gallop)
- Frankish wahtôn (S. English wake and watch) > Picard Old Norman wait(i)er (> English wait) ; Old French guaitier, French guetter
- Frankish *werra > Old Picard Old Norman werre, warre (> English war) ; French guerre (war)