Language/French/Grammar/Masculine-and-feminine-forms-of-adjectives-—-A-change-in-written,-but-not-spoken
General Rule
The general rule is that an -e is added to the masculine form of adjectives to produce the feminine form.
In cases where the masculine form ends in one of the following vowels or consonants, there is a change in the written form but not in the spoken form:
Tab1
NB: In the case of aigu, ambigu, contigu, a diaresis (ë) is added to the feminine -e in written French to indicate that the -u sound is maintained in spoken French (aigue would be pronounced rather like English 'egg' otherwise; compare long/longue).
Tab2
NB: In these cases, where the final r is pronounced in the masculine, a grave accent is added to the first written e.
Tab3
NB: In these cases, it is -le which is added and not just -e.
Tab4
NB: In these cases the / is pronounced in the masculine.
By contrast in the following adjectives the final -il is pronounced as indicated:
Tab5