Indefinite adjectives are used to talk about a noun without defining it precisely. They add a notion of quantity, totality, absence or vague precision. In quelques livres, plusieurs problèmes, tout le monde, aucun retard, the indefinite adjective provides information about the whole or the number, but does not say exactly how many or which one. Without it, the noun remains more neutral: livres, problèmes, monde, retard. With it, the meaning becomes more precise, even if the precision remains general. These forms are part of the group of adjectives, just like the forms studied in Formation de l'Adjectif et Accord de l'adjectif.

Quelques indicates a small non-exact quantity: quelques minutes, quelques amis. Plusieurs expresses a quantity greater than two, without giving a precise number: plusieurs pages, plusieurs voisins. Certains and certaines present a particular group among others: certains élèves ont fini, certaines rues sont fermées. These forms are used when you want to talk about a part of a set without counting it exactly. In a more literary context, certains can also suggest an approximate idea, as in certains jours de l’année. To reinforce the link with number and group, you find the same type of function as in Adjectifs numéraux, but here the exact digit disappears.

Vague quantity and estimation

Usage	Explanation
Small indefinite quantity	We use quelques to talk about a small quantity without counting exactly.
Larger quantity	We use plusieurs to indicate a quantity greater than a small number without specifying it.
Partial number	We use certains to show that only part of the group is involved.

Tout and its forms tous, toute, toutes express the totality of a set. With a singular noun, tout and toute mean that nothing is excluded: the whole country, the whole week. With a plural noun, tous and toutes designate the entirety of the elements: all the children, all the answers. The form depends on the noun it accompanies, as in Adjectifs démonstratifs, where the determiner agrees also with the noun. Here, the central idea is that of a complete totality, with no selection or limit.

Expression of totality

Usage	Explanation
Masculine singular whole	We use tout to talk about the totality of a masculine singular noun.
Masculine plural whole	We use tous to talk about the entirety of masculine elements in the plural.
Feminine singular whole	We use toute to talk about the totality of a feminine singular noun.
Feminine plural whole	We use toutes to talk about the entirety of feminine elements in the plural.

Aucun and nulle mark total absence: no problem, no evidence. They are used mainly in a formal or written register. Pas un expresses the same idea in a more direct way: not a word, not a single error. With these forms, the noun is presented as absent as a whole. In the sentence, aucun can occur with a strong negation or appear in constructions where the absence is already clear: I have no doubt. Pas un emphasizes the absolute zero, as in No guest arrived on time. For the comparative value of an absence or a higher degree of absence, we then move closer to Adjectifs comparatifs.

Marks of total absence

Usage	Explanation
Ordinary absence	We use aucun to say there is nothing at all in a common way.
Sustained absence	We use nul in a more formal register to express a total absence.
Emphatic absence	We use pas un to insist on the complete absence of a single element.

Each designates the elements one by one in a group: each day, each student. It imposes a distributive reading, because it looks at every element separately. Certain and certain present an element not identified with precision: certain details, certain people. Divers and diverses indicate several different elements within a set: various topics, different reasons. These words are not used for precise counting, but to organize the noun in a fuzzy or partial way. They are useful when you want to talk about a set without naming it entirely, as in descriptions close to Adjectifs relatifs, where the noun is also tied to a broader notion of reference.

Indeterminacy and distribution

Usage	Explanation
Individual distribution	We use chaque when considering elements one by one.
Element not identified	We use certain to talk about a being or thing without identifying it precisely.
Variety of several elements	We use divers to evoke several elements of different or varied nature.

Indefinite adjectives often agree in gender and number with the noun they accompany. We say quelques amis and quelques idées, certains projets and certaines solutions, toutes les maisons and tout le quartier. Some, however, remain tied to a fixed form depending on their use, like chaque, which does not take a plural ending. The position is usually before the noun: several days, no noise, diverse documents. When the indefinite adjective accompanies a definite noun group, it also comes before that group: all the children, none of these answers. This position before the noun aligns with the general functioning studied in Position de l'adjectif.

Agreement and placement of indefinite adjectives

Idea
The indefinite adjective agrees generally in gender and number with the noun it accompanies.
The indefinite adjective is placed most often before the noun.

Tout can be an adjective or an adverb. As an adjective, it accompanies a noun and agrees with it: the whole village, the whole day, all the children, all the streets. As an adverb, it modifies an adjective and remains basically invariable: very small, very happy, very ready. The adjective is recognizable because it modifies a noun; the adverb is recognizable because it modifies a preceding adjective. Before a feminine adjective starting with a consonant or a h-aspirate sound, tout can agree in speech and in writing: toute contente, toutes fières. This distinction matters a lot for reading and writing correctly the forms related to tout.

Meanings of tout depending on context

Idea
Tout is an adjective when it accompanies a noun and agrees with it.
Tout is an adverb when it modifies an adjective and remains invariable in most cases.