French Adjectives - Les adjectifs français

As French adjectives must agree in gender and number with the noun they describe, their masculine, feminine and plural forms must be known. You already know that most adjectives in French are regular. Let's study the others.

Gender

Five adjectives have two masculine forms.
The form ending in l is used before a noun beginning in a vowel.

beau, bel

un beau château, un bel appartement

nouveau, nouvel

un nouveau siècle, le nouvel an

vieux, vieil

un vieux monsieur, un vieil homme

Although the pair fou and fol exists, fol never appears except in set phrases: un fol espoir, un fol amour, that seem a little affected.
The pair mou - mol is used only for comical effects, and not very good ones.

Most French adjectives end in e in the masculine form, so the feminine form is the same. For most of the other adjectives, the feminine is usually signalled by adding -e.

A minority have their own rules.

All adjectives ending in -f make the feminine in -ve

abrasif, actif, chétif, décisif, fautif, massif, naïf, neuf, vif ...
abrasive, active, chétive, décisive, fautive, massive, naïve, neuve, vive ...

Adjectives ending in -er change to -ère:

amer, dernier, entier, léger ...
amère, dernière, entière, légère ...

Adjectives ending in -s double it before adding -e

bas, gras, gros, épais, exprès, las, métis...
basse, grasse, grosse, épaisse, expresse, lasse, métisse...

Adjectives ending in -el -en -on double the final consonant:

actuel, mensuel, visuel ... ancien, italien, moyen ...
actuelle, mensuelle, visuelle ... ancienne, italienne, moyenne ...

Adjectives ending in -in -un -al do not double the final consonant (they are perfectly regular):

fin, brun, normal...
fine, brune, normale...

There is no absolute rule for adjectives ending in -an -il -ot -ul, some double, some don't, before adding -e.

paysan, paysanne; persan, persane
gentil, gentille; civil, civile
sot, sotte; idiot, idiote
nul, nulle; seul, seul...

Some adjectives ending in -et double the last consonant before adding -e(most are diminutive):

aigrelet, blet, douillet, fluet, gentillet, grassouillet, guilleret, longuet, maigrelet, muet, net, rondelet, simplet, violet...
aigrelette, blette, douillette, fluette, gentillette, grassouillette, guillerette, longuette, maigrelette, muette, nette, rondelette, simplette, violette...

Some other are written -ète(same pronunciation as -ette):

complet, concret, désuet, discret, indiscret, incomplet, inquiet, replet, secret...
complète, concrète, désuète, discrète, indiscrète, incomplète, inquiète, replète, secrète...

Almost all adjectives ending in -x make the feminine in -se

amoureux, ennuyeux, heureux, jaloux, sérieux...
amoureuse, ennuyeuse, heureuse, jalouse, sérieuse...

The main exceptions are:
doux, roux, faux, vieux
douce, rousse, fausse, vieille

Some adjectives are completely irregular:

aigu, ambigu, andalou, benin, blanc, caduc, coi, favori, fou, frais, franc, grec, long, malin, mou, oblong, public, sec, turc ...
aiguë, ambiguë, andalouse, benigne, blanche, caduque, coite, favorite, folle, fraîche, franche, grecque, longue, maligne, molle, oblongue, publique, sèche, turque ...

Adjectives ending in -eur form the feminine in -eure -euse -rice -eresse (rare).
The rule is: they must be learnt.

antérieur, moqueur, destructeur, enchanteur...
antérieure, moqueuse, destructrice, enchanteresse...

As often, spelling French is more complex than pronouncing it. For example: -ane and -anne or -ette and -ète sound alike. Always focus on the spoken language. When you write, you have plenty of time to check a word in a dictionary.

Number

An adjective is made plural usually by adding -x or -s.
This rule applies to most masculine adjectives and nearly 100% of feminine adjectives.
What to do with the rebels?

Add -x to adjectives ending in -eau:

beau, nouveau...
beaux, nouveaux...

Adjectives ending in -al form the plural by changing -al to -aux:

légal, royal...
légaux, royaux ...

astral, banal, fatal, final, natal, naval...
are made plural by adding -s.
(finaux is more and more often said, even written. It began as a joke because finaud exists, it means "wily", and it is now overspreading.)

Except for adjectives of colour, in a compound adjective each variable part varies:

des garçons sourds-muets
des pièces tragi-comiques

Notice that invariable part remains invariable:

des films hispano-lusitaniens
des pays sud-américains

When the adjective of colour is a compound adjective or can be a noun used as an adjective, it is invariable:

des robes vert bouteille, des yeux bleu foncé, des lèvres rouge cerise ...
des chemises ivoire, des gants orange, des yeux marron ...
Des fleurs roses

Alone in its category: hébreu, hébreux.

Adjectives (mainly adjectives of color) created from a noun vary neither in gender nor in number:
une jupe marron, des yeux turquoise.
Remember: rose must agree with the noun it refers to: des éléphants roses.