Why is the "h" added in "blanche"? Shouldn't it just be "blance"?
Why is it that the feminine form of the word "blanc" is "blanche"? I'd thought that the feminine form of adjectives meant that the words would just end in an "e." For example, the word "vert" vs "verte." And does this mean that all adjectives that end in "c" have to be changed to "che" instead of "ce" when used on a feminine object?
Les adjectifs se terminant par un «C» forment leur féminin en «QUE» ou en «CHE» : PUBLIC devient alors PUBLIQUE et FRANC devient FRANCHE.
Il existe toutefois une exception pour le mot GREC qui conserve son «C» et auquel on doit ajouter «QUE» / GRECQUE
WHY? This is what schoolchildren learn at school, we do not tell them why. Millions and millions of Francophones do not know the reason for this singularity. Perhaps philologists know it? Certainly an explanation must be sought for the archaic formation of French from Latin.
Personally, I know the rule, like everyone else who learnt it, but I do not know the historical reason...
This is not always the case. Sometimes, the feminine version of words may be replacing an "-el" ending with "-elle", or "-eur" with "ere" (there may be an accent on the first "e", but it depends on the word). For "blanc", the feminine form is "blanche" because that is just how it is. Vocally, I think it would not be "right", for a lack of better words. Not all words follow the "e" rule. Some words don't even have a "feminine" form, as they can be defaultly masculine (meaning whether the object is feminine or masculine, the word is not altered). I'm sorry that I could not explain it the best of my ability, for there are many exceptions when it comes to French grammar, and not all words follow a singular rule. Though, I hope this helps a little!