In Italian, indefinite articles (articoli indeterminativi) correspond to the English words a and an. They are used before singular nouns when talking about a person, animal, or thing that is not specifically identified or is mentioned for the first time. Unlike English, Italian has four forms: un, uno, una, and un'. The correct form depends on the noun's gender (masculine or feminine) and the sound at the beginning of the following word.
Ho un libro. — I have a book.
Vedo una ragazza. — I see a girl.
Masculine Indefinite Articles
The most common masculine indefinite article is un. It is used before nouns beginning with a vowel or most consonants. Unlike the definite article l', the article un never takes an apostrophe, even before a vowel. The form uno is used before words beginning with s followed by another consonant, as in studente, or with z, as in zaino. These are the same common beginnings that require the masculine definite article lo.
un libro — a book
un ragazzo — a boy
un amico — a friend
uno studente — a student
uno zaino — a backpack
Feminine Indefinite Articles
Feminine nouns use una before consonants and un' before vowels. The apostrophe in un' shows that the final a of una has been removed. This is an important difference from masculine un, which never requires an apostrophe. Notice the difference between un amico and un'amica: the first is masculine and has no apostrophe, while the second is feminine and requires one.
una casa — a house
una ragazza — a girl
un'amica — a female friend
un'isola — an island
Italian indefinite articles have no plural forms. To express an indefinite quantity in the plural, Italian can use other constructions, including partitive articles, which are explained separately.
Summary of Italian Indefinite Articles
| Gender | Beginning of the following word | Article | Example |
| Masculine | Most consonants | un | un libro |
| Masculine | Vowel | un | un amico |
| Masculine | s + consonant, z | uno | uno studente |
| Feminine | Consonant | una | una casa |
| Feminine | Vowel | un' | un'amica |