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Did you ask L’Académie française? They know everything. Just ask them.

• K0SM0S 7y ago
  Ha, you made me curious. Do you think they would actually reply to emails?! — though it would probably be faster to Google for a good manual or teacher's blog. Btw more than "knowing", it's the official institution that officially decides on linguistic rules and their evolution, for the French language in France. It's called "prescriptivism" (higher authority decides what's right and what's not, period) as opposed to "descriptivism" (such as the American English language, for which nobody gets to make these calls, and dictionaries merely follow usages by people).