Indefinite articles: un, una, unos, unas

Necesito un libro.I need a book.

Spanish marks a noun as one thing, or some things, among many — not yet identified — with a small word that agrees with that noun's gender and number: un, una, unos, unas.

Quick shortcut: masculine singular → un. Feminine singular → una. Masculine plural → unos. Feminine plural → unas.

The four forms

• un libro (a book) → unos libros (some books)
• una mesa (a table) → unas mesas (some tables)

The form always matches the noun it introduces, not the person talking — see Noun gender (masculine & feminine) for how a noun gets its gender in the first place, and Plural nouns for how the noun itself changes in the plural.

Unos and unas can also mean "some" or "a few"

English switches words for the plural — a book becomes some books, not a books. Spanish just uses the plural form of the same article:

• Compré unas manzanas. (I bought some apples.)
• Tengo unos amigos en Madrid. (I have some friends in Madrid.)

Unos/unas before a number: "about"

Right before a number, unos/unas doesn't mean "some individual items" — it means an approximate quantity, like English "about" or "around":

• Llegamos en unos veinte minutos. (We'll arrive in about twenty minutes.)
• Había unas cien personas. (There were about a hundred people.)

When Spanish drops the article that English keeps

English normally uses a/an before a singular profession noun. Spanish usually leaves the article out after ser — unless the profession is modified by an adjective:

• Ella es profesora. (She's a teacher.) — ✅ no article
• Ella es una profesora excelente. (She's an excellent teacher.) — ✅ the article often comes back once the profession is described this way — though it's a tendency, not a strict rule; Ella es buena profesora (still no article) is also fine

With otro/otra ("another"): otro already means "a different one" all by itself, so it never takes un/una in front of it.

• Necesito otro café. (I need another coffee.)

In exclamations with qué:

• ¡Qué problema! (What a problem!)
• ¡Qué buena idea! (What a good idea!)

Common mistakes

• ❌ Ella es una médica. → ✅ Ella es médica. (no article with a plain, unmodified profession)
• ❌ un otro coche → ✅ otro coche (otro never takes the indefinite article)
• ❌ ¡Qué un problema! → ✅ ¡Qué problema! (no article after qué in an exclamation)
• ❌ un mesa → ✅ una mesa (the article has to match the noun's gender, not just be "close enough")

Quick check

Fill in the blank with the right form of un/una/unos/unas, or write "—" if no article is needed.

1. Necesito ___ lápiz. (pencil)
2. Ella es ___ enfermera. (nurse)
3. Tengo ___ preguntas. (questions)
4. Es ___ profesor excelente. (an excellent teacher)
5. Prefiero ___ otro color. (another color)
6. Había ___ treinta personas. (about thirty people)

Key takeaways

• Four forms, matching gender and number: un (masc. sing.), una (fem. sing.), unos (masc. pl.), unas (fem. pl.).
• The plural forms also translate English "some" or "a few": unas manzanas (some apples).
• Right before a number, unos/unas means "about": unos veinte minutos.
• Spanish drops the article where English keeps it: an unmodified profession after ser, with otro, and in qué exclamations.
• The article still has to agree with the noun even in those cases where it's used — mismatched gender or number is a genuine error, not a style choice.