A and an are used to introduce a singular noun without specifying which. They announce a thing, a person or an animal not identified or mentioned for the first time. In I buy a book, the book is not known to the reader. If the article disappears, the sentence loses this introductory idea and becomes incomplete or changes meaning. Indefinite articles are placed before the noun, like the Articles in general, and they often work with a complement added after the noun, for example a wooden table or a friend from Paris.

Introduction of a singular noun

Idea
We use un or une to introduce a singular noun still unknown.
We use un or une when talking about a new element in discourse.

The choice between un and une depends on the gender of the noun. With a masculine noun, one uses un: un stylo, un frère, un café. With a feminine noun, one uses une: une chaise, une sœur, une ville. The article does not indicate the number here, only the gender and the singular. When the noun changes gender, the article changes too, even if the object remains the same in reality: un ami but une amie. This difference is found throughout the noun phrase, as with the Definite Articles and the Partitive Article, where the gender also guides the form.

Choice according to the gender of the noun

Idea
We choose un in front of a masculine noun.
We choose une in front of a feminine noun.

In the plural, the indefinite article takes the form des. It introduces several people, objects or ideas without identifying them precisely: des livres, des voitures, des enfants. It is used when talking about a non-specified whole, not a group already known. In They bought apples, we know there are several apples, but not which ones. Des sits directly before the plural noun, then the noun retains its plural form. To talk about several elements without specifying which ones, this is the normal form, unlike the Absence of article, which removes any determination.

Use of the plural article

Idea
We use des to talk about several unspecified nouns.
We keep des when we do not want to specify the exact quantity.

Before a word that begins with a vowel, un stays un and une stays une. We say un ami, un hôtel, une idée, une école. In speech, liaison can appear between the article and the noun, especially with un before certain vowels or certain silent hs, as in un ami or des amis. The article does not change form to avoid contact with the vowel, unlike other French articles. The noun remains placed right after the article, with no middle word.

Form before its initial

Usage	Explanation
Before a consonant	We use un or une when the noun starts with a consonant.
Before a vowel	In speech, un and une remain used before a vowel without special change.

After a negation, the indefinite article becomes de or d’ before a vowel. We say Je n’ai pas de voiture, Elle n’a pas d’amis, Nous ne voyons pas de problème. Negation removes the idea of quantity or existence marked by un, une, des and replaces it with an absence. The same form appears after a quantity expression: beaucoup de livres, peu de temps, une tasse de thé, un kilo de pommes. The noun follows de directly, with no indefinite article after the quantity.

Change after negation and quantity

Idea
After a negation, un une and des often become de.
After an expression of quantity, des is replaced by de.

After certain verbs and common expressions, the indefinite article disappears. One says to be a teacher, to become a doctor, to be hungry, to scare, to catch a cold. The noun or the following expression then describes a state, a function or a general sensation, without an article. In He is an engineer, the profession is presented as a characteristic. In I am hungry, hunger expresses a bodily state. The absence of an article is not free here: it belongs to these fixed and frequent constructions, just as some phrases studied with the Definite Articles or the Absence of article.

Absence of the article with certain verbs

Usage	Explanation
Preference or desire	After certain verbs like aimer or vouloir, the article can disappear in a general sense.
Profession or role	After verbs like être, one often puts an absent article to talk about a profession or function.

The indefinite article introduces a new, unidentified noun, or an element among others: I saw a dog. The definite article refers to a known, unique, or already mentioned being: The dog was black. The choice depends on the context. On first contact, the indefinite introduces; then the definite takes over. We also use the definite to talk about an entire category: Dogs like to run. With names of profession, state or fixed expression, the article may disappear, but otherwise the contrast between un, une, des and the Definite Articles organizes how the noun is presented in the sentence.

Choice according to the context

Usage	Explanation
New introduction	We choose a an or des to introduce someone or something new.
Known object	We choose the the or the when the noun is already identified or known from the context.