Nowadays it's mostly only the case on the letter <e>, where it indicates a pronunciation of /ɛ/. In the past, when put on a <a> it changed it from /a/ to /ɑ/,

Nowadays it's mostly only the case on the letter <e>, where it indicates a pronunciation of /ɛ/. In the past, when put on a <a> it changed it from /a/ to /ɑ/, however that mostly fell in disuse in most French French dialects and I can only hear the distinction consistently in Canadian French dialects.