[Originally posted on 05/06/12 on the Duolingo French for English speakers forum by ricainrico]
Regular plurals:
Most of the time, we simply add an “s” to a noun to make it plural (if it doesn’t have one already, or if it ends with an “x” or “z”).
Irregular plurals:
When the noun ends in “‘-al”, the plural ending is “-aux”, e.g. un animal – des animaux; un cheval – des chevaux, un bocal – des bocaux, etc. (These are all masculine nouns.)
(Note: there are a few exceptions to this rule, e.g. un festival – des festivals, NOT: des festivaux.)
Consequently, the same rule applies to adjectives ending in “-al” when modifying masculine, plural nouns, e.g. un animal tropical – des animaux tropicaux.
Generally, if a noun ends in “-eu”, “-eau” or “-au”, it takes an “x” in the plural, e.g. un feu – des feux, un agneau – des agneaux, etc.
Also there are precisely 7 nouns ending in “-ou” which take an “x” rather than an “s” in the plural: bijou, caillou, chou, genou, hibou, joujou, pou.
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