Indefinite Articles (Un, Una, Unos, Unas) | Spanish (Latin America) Grammar

The Spanish indefinite article corresponds to English a/an in the singular and some or a few in the plural. Like the definite article, it has four forms and must agree with its noun in gender and number.

The Four Forms

	Singular	Plural
Masculine	un	unos
Feminine	una	unas

The singular forms un and una mean a or an. The plurals unos and unas mean some, a few, or several — they are used when you want to mention an unspecified quantity.

Tengo un hermano y una hermana.

I have a brother and a sister.

Compré unos libros y unas revistas.

I bought some books and some magazines.

Singular: A / An

In the singular, the indefinite article introduces a new, non-specific item — something the listener has not heard about yet.

Hay un gato en el jardín.

There is a cat in the garden.

Necesito una silla más.

I need one more chair.

Notice how the first mention uses un, but once the cat is known you would switch to el gato. This parallels the English a → the transition.

Plural: Some / A Few

The plural forms are often optional in Spanish — you can just use a bare plural noun. But unos/unas adds the flavor of "some" or "a few of them."

Vi unas nubes en el cielo.

I saw some clouds in the sky.

Había unos turistas en la plaza.

There were some tourists in the square.

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Unos/unas before a number means approximately: unos veinte años = "about twenty years." This is a very common way to estimate.

When to Omit It

Spanish drops the indefinite article in several contexts where English would use one. See Article Omission for the full list.

Context	Spanish	English
Profession	Soy médico.	I am a doctor.
Nationality	Es mexicana.	She is a Mexican.
Religion	Es católico.	He is a Catholic.
After sin, con	Vino sin abrigo.	He came without a coat.
After tener (general)	No tengo carro.	I don't have a car.

Mi madre es profesora.

My mother is a teacher.

Salí sin paraguas.

I left without an umbrella.

The article reappears, however, when the noun is modified. Compare:

Es profesora. / Es una profesora excelente.

She is a teacher. / She is an excellent teacher.

With the adjective excelente added, the article comes back. This is a reliable rule: unmodified profession or role = no article; modified = article.

Difference from Definite Article

El/la/los/las point to something specific and known.
Un/una/unos/unas introduce something new or unknown.

Un hombre llamó. El hombre dejó un mensaje.

A man called. The man left a message.

The first mention uses un (new to the listener); the second uses el (now known from context).

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Think of indefinite articles as first-mention markers. Once an item is on the table, switch to the definite article.

Quick Recap

Four forms: un, una, unos, unas.
Singular = a/an, plural = some/a few or approximately.
Omitted before unmodified profession, nationality, or religion.
Reappears when the noun carries an adjective or other modifier.

Common mistakes

❌ Soy un doctor.

Wrong: no article before unmodified professions after ser.

✅ Soy doctor.

Correct: drop un/una with unmodified professions.

❌ Ella es una mexicana.

Wrong: no article before unmodified nationalities after ser.

✅ Ella es mexicana.

Correct: nationality without article after ser.

❌ Tengo un hambre.

Wrong: idiomatic tener expressions use no article.

✅ Tengo hambre.

Correct: tener + bare noun for physical sensations.