French Complex Plurals (des chefs-d'œuvre)

• Compound Gender: For most compound nouns, the gender is established by the head noun. For example, un chou-fleur is masculine because chou is masculine. Similarly, une plate-forme (platform) is feminine because plate acts as an adjective preceding the feminine noun forme, or forme is the head noun. Even if the first word is a verb, the overall gender usually defaults to masculine if not explicitly indicated by a noun, or it follows a common convention for the implied object.

• Adjective Agreement within Compounds: In Adjective + Noun compounds, the adjective agrees in both gender and number with the noun it modifies. If the noun is feminine, the adjective takes its feminine form.
• un coffre-fort (safe - masc.) -> des coffres-forts (masc. plural)
• une plate-forme (platform - fem.) -> des plates-formes (fem. plural)

• Historical Invariability of grand: The adjective grand historically remained invariable before feminine nouns in some compound constructions. While the 1990 reforms encourage agreement, both forms can still be encountered, particularly in established expressions. For instance:
• Traditional: une grand-mère -> des grand-mères (though grands-mères is common)
• Modern/1990: une grand-rue (main street) -> des grandes-rues (explicit agreement)
• However, for grand-mère, grands-mères is now the widely accepted and preferred plural, highlighting a shift towards more regular agreement even in semi-fixed expressions.

No. The 1990 Rectifications Orthographiques are recommendations, not strict obligations. Both traditional and reformed plurals are officially considered correct. However, consistency within a text is highly advised, and many modern publications and educational institutions now favor the simplified forms. For example, des évènements (reform) is now often preferred over des événements (traditional), but both are acceptable.

The core principle is that only nouns and adjectives can pluralize. Verbs, adverbs, and prepositions remain invariable. For Noun + Noun and Adjective + Noun compounds, generally both elements pluralize. For Noun + Preposition + Noun, only the first noun pluralizes. For Verb + Noun, the verb is invariable, and the noun's pluralization depends on traditional semantic logic or the 1990 reform (often adding -s).

Some compound nouns are truly invariable, typically those where all components are naturally singular or invariable parts of speech (e.g., des laissez-passer, des va-et-vient). Others, particularly very old or highly idiomatic expressions, may have historical plural forms that don't immediately align with the general rules (e.g., des pistolets-mitrailleurs where mitrailleur is traditionally singular, but 1990 reform would make it mitrailleurs). These often require individual memorization.

For a C2 learner, the choice is often stylistic or guided by the context and audience. In formal or academic writing, you might research the preferred style guide or lean towards traditional forms if you aim for a more classic tone. In everyday communication, the 1990 reform plurals (des après-midis, des gratte-ciels) are widely accepted and can make your French sound more contemporary. Crucially, choose one system and stick to it within a single piece of writing.

Yes, indirectly. The gender of the compound noun (usually determined by its first noun or head noun) influences the agreement of any external adjectives or pronouns. Within the compound, adjectives will agree in gender and number with the noun they modify (e.g., une plate-forme -> des plates-formes). The historical invariability of grand before feminine nouns in some compounds (grand-mère) is a notable point, though modern usage often favors agreement (grands-mères).

Yes. The plural -s on a noun at the end of a compound can trigger liaison if the next word begins with a vowel or silent h. For example, in des chefs-d'œuvre, the s of chefs is often silent unless followed by a vowel or mute h (e.g., des chefs-d'œuvre incroyables would likely have liaison on chefs). Similarly, the x in words like choux in des choux-fleurs is silent, but the x in choux (plural of chou) can also trigger liaison if followed by a vowel or mute h (e.g., des choux excellents). Pay attention to phonological nuances to sound genuinely native.