In words like payer /peje/, pied /pje/, œil /œj/, paille /paj/, if I were to replace the /j/ with /i/ so these words become /peie/, /pie/, /œi/ and /pai, would there be any differences in pronunciation because I can't hear them at all. To me, /j/ sound just like /i/ except in positions like fille /fij/ where /j/ can't be replaced by /i/ because the /j/ in fille is made differently than the /j/ in /peje/.
So two questions:
Can /j/ be replaced by /i/?
Why is it that in fille /fij/ the /j/ kind of sounds like a downard glide (something like the /j/ sound from the english word 'yuck') while in all the other words I mentioned, it just sounds like /i/?