French Plural Formation Rules

French nouns and adjectives typically form plurals by adding -s, but the language has numerous specific patterns and exceptions.

Many words follow special rules based on their singular endings, while others have completely irregular forms inherited from Old French.

Basic Rules

The standard rule is adding -s to the singular form (maison → maisons).

However, words ending in -s, -x, or -z remain unchanged (prix → prix).

Words ending in -au, -eau, and -eu typically add -x instead of -s (bateau → bateaux).

Special -al and -ail Endings

Most words ending in -al change to -aux in plural form (journal → journaux), though some modern words like festival follow the regular -s rule.

Similarly, certain words ending in -ail change to -aux (travail → travaux), while others follow regular patterns.

Words Ending in -ou

While most words ending in -ou simply add -s, seven common nouns take -x instead:

  • bijou → bijoux (jewelry)
  • caillou → cailloux (pebble)
  • chou → choux (cabbage)
  • genou → genoux (knee)
  • hibou → hiboux (owl)
  • joujou → joujoux (toy)
  • pou → poux (louse)

Invariable Words

Several French words remain unchanged in plural form, including:

  • Many words ending in -s or -x (temps, voix)
  • Certain Latin/Greek borrowings (virus, atlas)
  • Abstract nouns (pathos, cosmos)

Compound Words

French compound words follow specific patterns based on their components:

  • Noun + Adjective: both elements take plural (année-lumière → années-lumière)
  • Verb + Noun: typically only the noun changes (porte-monnaie → porte-monnaie)
  • Noun + Preposition + Noun: only the first noun usually changes (arc-en-ciel → arcs-en-ciel)

Completely Irregular Forms

Some common French words have unique plural forms:

  • œil → yeux (eye)
  • monsieur → messieurs
  • madame → mesdames
  • aïeul → aïeux (ancestor)
  • ciel → cieux (heaven/sky)