Spanish has four forms of the indefinite article — un, una, unos, unas — corresponding roughly to English a/an in the singular and some / a few in the plural. Three things make them harder than they look. First, they agree with the noun in gender and number, so you have to know whether you are dealing with a masculine or feminine noun before you choose. Second, the plural unos/unas covers a meaning English usually expresses with some or a few, plus an extra meaning (around, approximately) that English does not. Third, and most importantly for English speakers, Spanish drops the indefinite article in several places where English keeps it — especially with professions, nationalities, and a handful of fixed prepositional patterns.
This page covers all four forms, agreement, the un agua rule (the indefinite version of the famous el agua rule), the approximate-quantity use of unos/unas, and the seven contexts where Spanish learners should leave the article out.
The four forms
Spanish indefinite articles agree with the noun in gender and number:
| Singular | Plural | |
|---|---|---|
| Masculine | un | unos |
| Feminine | una | unas |
Necesito un boli y una hoja de papel para apuntar el número.
I need a pen and a sheet of paper to write down the number.
Hay unos niños jugando en el parque y unas señoras tomando el sol.
There are some kids playing in the park and some women sunbathing.
The singular forms (un, una) translate as a/an. The plural forms (unos, unas) translate as some or a few — and as you will see below, also as around with numbers.
Agreement: pick the form by the noun's gender
Because the form depends on the noun, learners have to know the noun's gender first. The gender system is treated in detail on its own page; the short version is that -o nouns are usually masculine (un libro, un coche) and -a nouns usually feminine (una mesa, una casa), with a handful of high-frequency exceptions like el problema, el día, la mano, la foto.
Tengo un problema bastante gordo con el coche.
I've got a pretty big problem with the car. — un problema (masculine despite ending in -a).
Saqué una foto preciosa del atardecer.
I took a beautiful picture of the sunset. — una foto (feminine despite ending in -o).
Get the gender wrong and the article will clash with the rest of the sentence — un foto bonito would be three mismatches in three words and would jar any native ear.
The un agua rule — feminine nouns starting with stressed /a/
The same phonological rule that produces el agua (instead of la agua) also applies in the indefinite. Feminine singular nouns beginning with a stressed /a/ (spelled a- or ha-) take un rather than una in standard Peninsular writing:
Pídeme un agua sin gas, por favor.
Get me a still water, please. — un agua, not una agua, even though agua is feminine.
Tengo un hambre de lobo, llevo todo el día sin comer.
I'm starving — I've been all day without eating. (literally 'a wolf's hunger')
The noun is still grammatically feminine, so adjectives following it agree feminine:
Vi un águila enorme volando sobre el barranco.
I saw an enormous eagle flying over the gorge. — un águila but enorme (invariable here); compare un águila majestuosa with feminine adjective.
As with el, the rule applies only to singular, stressed /a/ at the very start, with the article immediately preceding the noun. The plural reverts to feminine (unas aguas, unas águilas), and unstressed initial a- keeps una (una amiga, una academia, una abuela). If an adjective intervenes between article and noun, una comes back (una preciosa águila).
Plural unos / unas — "some, a few, around"
In the plural, unos and unas cover two distinct meanings that English splits between some/a few and around/approximately.
Indeterminate quantity — "some, a few"
He comprado unas manzanas en el mercado, ¿quieres una?
I've bought some apples at the market — do you want one?
Hay unos mensajes sin leer en el móvil.
There are some unread messages on the phone.
This use parallels English some or a few. It often disappears in Spanish (see omission below), so when you do use unos/unas you are deliberately signalling that there is a small, unspecified quantity.
Approximate quantity — "around, about"
This is the one English speakers tend to miss. With a number, unos/unas means approximately — a hedged estimate, like saying around or about in English.
Vinieron unos veinte invitados, no me esperaba a tanta gente.
Around twenty guests came — I wasn't expecting that many people.
La reunión durará unas dos horas, calculo yo.
The meeting will last about two hours, I reckon.
Tendrá unos cincuenta años, no le echo más.
He must be around fifty — I wouldn't say any older.
Choose unos or unas by the gender of what is being counted (unos veinte invitados — masculine plural; unas dos horas — feminine plural). This unos = around idiom is extremely common in everyday speech; learners who do not use it sound textbook-stiff.
When NOT to use the indefinite article
This is where English instinct misleads most. Spanish drops un/una/unos/unas in several common contexts where English keeps a/an or some.
1. Professions, nationalities, religions after ser
After ser used to identify someone's profession, nationality, religion, ideology, or social role, Spanish uses a bare noun:
Mi hermana es médica en un hospital de Madrid.
My sister is a doctor at a hospital in Madrid. — bare médica, no una.
Soy profesor de español desde hace diez años.
I've been a Spanish teacher for ten years. — bare profesor.
Pablo es catalán pero vive en Sevilla.
Pablo is a Catalan but lives in Seville.
English forces a here (a doctor, a teacher, a Catalan); Spanish forbids it as the default. The reason is that the noun is functioning like an adjective — it classifies the subject rather than introducing a new entity into the discourse.
The article comes back as soon as the noun is modified by an adjective or qualifying phrase:
Mi hermana es una médica excelente, todos sus pacientes la adoran.
My sister is an excellent doctor — all her patients love her. — una returns because of excelente.
Soy un profesor con bastante experiencia en grupos pequeños.
I'm a teacher with quite a bit of experience in small groups. — un returns because of the qualifying phrase.
This is the deeper logic: bare noun = pure classification (she is a doctor = doctor-category); article + adjective = a description of an individual (she is an excellent doctor = a particular kind of doctor).
2. After sin — "without"
Salí de casa sin paraguas y me empapé entero.
I left the house without an umbrella and got soaked.
Lleva meses sin trabajo, está desesperado.
He's been without a job for months, he's desperate.
English needs an, a; Spanish drops the article when the noun is the obvious complement of sin. Adding un/una would force a specific reading (sin un paraguas = "without a single umbrella," with emphasis on the count).
3. After con in fixed patterns
¿Tomas el café con leche o solo?
Do you take your coffee with milk or black?
Quiero un bocadillo con jamón y tomate.
I want a sandwich with ham and tomato.
When con introduces a typical accompaniment or ingredient (not a specific countable item), Spanish goes bare. Con una leche would mean "with one [serving of] milk."
4. After buscar, tener, necesitar with non-specific things
When you are looking for, have, or need a non-specific instance of something — especially something you typically own one of — Spanish often drops the article:
Busco trabajo desde febrero, pero el mercado está fatal.
I've been looking for a job since February, but the market is awful.
¿Tienes coche o vas en metro?
Do you have a car or do you take the metro?
No tengo perro porque mi piso es muy pequeño.
I don't have a dog because my flat is very small.
Compare with Busco un trabajo en una multinacional — once you specify what kind, the article reappears.
5. With otro / otra
This trips up almost every English speaker. Otro and otra mean "another," and Spanish does not put an article before them:
¿Me pones otra caña, por favor?
Could I get another (small) beer, please?
Volvimos a Granada al cabo de otro año.
We went back to Granada after another year.
The English instinct is to translate another as un otro, by analogy with un libro. This is wrong — otro already carries the indefinite meaning. Un otro simply does not exist in modern Spanish.
6. In exclamations and bare-noun lists
¡Qué día tan largo!
What a long day! — qué + bare noun in exclamations, no un.
Compré pan, leche, huevos y unas naranjas para el desayuno.
I bought bread, milk, eggs and some oranges for breakfast. — bare mass nouns in shopping lists; unas marks a countable subset.
After qué in exclamations, Spanish never uses un/una — the English "what a ..." pattern simply does not carry over.
7. After negation, with non-specific quantity
No tengo ni idea de dónde lo he dejado.
I have no idea where I've left it. — bare idea after ni.
No hay manera de que cambie de opinión.
There's no way he'll change his mind.
For deeper treatment of when Spanish drops articles altogether, see omission of articles.
Un/una vs uno/una and position
The masculine number uno drops its -o whenever it sits directly before a masculine noun, so un doubles as the indefinite article and the front of the number "one." Context and intonation disambiguate:
—¿Cuántos hijos tienes? —Solo uno, una niña de cuatro años.
—How many children do you have? —Just one, a girl of four. — uno stands alone; una niña is article + noun.
To force the "one" reading unambiguously, Spanish often uses un solo (one single): un solo libro = "a single book."
The article comes before the noun and any pre-noun adjective, and does not combine with possessives or demonstratives — un mi libro and un este libro are both impossible. The exception is the long-form possessive, which appears after the noun and tolerates an article in front:
Un amigo mío me contó la historia, no me la inventé.
A friend of mine told me the story, I didn't make it up.
Common Mistakes
❌ Soy un profesor.
Incorrect when stating a profession alone — Spanish drops un/una before unmodified professions, nationalities, religions after ser.
✅ Soy profesor. / Soy un profesor con mucha paciencia.
Bare noun for pure classification; article returns when the noun is modified.
❌ Quiero un otro café.
Otro / otra never takes an article — un otro is impossible in Spanish.
✅ Quiero otro café.
Otro already carries the indefinite meaning. Same with otra: dame otra oportunidad, not una otra oportunidad.
❌ Salí sin un paraguas y me mojé.
After sin, Spanish drops the indefinite article for generic 'a' — un paraguas would force a 'a single umbrella' reading.
✅ Salí sin paraguas y me mojé.
Bare paraguas after sin. The article comes back if you specify: sin un paraguas decente.
❌ Una agua, por favor.
Feminine singular nouns starting with stressed /a/ take un, not una — the same euphony rule as el agua.
✅ Un agua, por favor. — Y unas aguas con gas para la mesa de al lado.
Un agua (singular); the plural reverts to feminine: unas aguas.
❌ Vinieron veinte invitados más o menos.
Awkward; the natural Spanish way to say 'around twenty' is unos veinte.
✅ Vinieron unos veinte invitados.
Unos + number = around / approximately. Choose unos / unas by the gender of the counted noun: unas dos horas.
❌ ¿Tienes un coche?
Not strictly wrong, but sounds like you mean 'a specific car' or 'one car.' For the generic question, drop the article.
✅ ¿Tienes coche?
Bare coche after tener for the generic 'do you own a car?' question — same with tener perro, tener trabajo, tener novio.
Key Takeaways
- Four forms — un, una, unos, unas — agree with the noun in gender and number.
- Feminine singular nouns starting with stressed /a/ take un, not una (un agua, un águila, un hambre), but stay feminine grammatically.
- Plural unos / unas covers both English some / a few and approximate quantity (unos veinte = around twenty). Use it for both.
- Drop the indefinite article with: bare professions/nationalities/religions after ser; after sin; after con in fixed patterns; after buscar/tener/necesitar for non-specific things; before otro/otra; after qué in exclamations; in many negated and bare-noun patterns.
- The article comes back as soon as the noun is modified by an adjective or qualifying phrase: soy profesor but soy un buen profesor.
- Do not stack un/una with possessives or demonstratives — Spanish picks one determiner per noun phrase.
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