Four-Form Adjectives (-o/-a/-os/-as) | Spanish (Latin America) Grammar

The most common type of Spanish adjective is the four-form adjective. These adjectives end in -o in their base (masculine singular) form and change their ending to match the gender and number of the noun they describe.

The Four Forms

A four-form adjective has one ending for each combination of gender and number:

	Masculine	Feminine
Singular	-o	-a
Plural	-os	-as

Take alto (tall) as an example:

Form	Example phrase	Translation
alto	un chico alto	a tall boy
alta	una chica alta	a tall girl
altos	unos chicos altos	(some) tall boys
altas	unas chicas altas	(some) tall girls

Mi hermano es alto.

My brother is tall.

Mi hermana es alta.

My sister is tall.

Mis primos son altos.

My (male) cousins are tall.

Mis primas son altas.

My (female) cousins are tall.

Common Four-Form Adjectives

Most descriptive adjectives you'll learn follow this pattern:

Masculine	Feminine	Meaning
bonito	bonita	pretty
pequeño	pequeña	small
rojo	roja	red
nuevo	nueva	new
viejo	vieja	old
blanco	blanca	white
negro	negra	black
amarillo	amarilla	yellow
frío	fría	cold
caliente	caliente	hot (two-form!)

Notice that caliente is included as a reminder: not every adjective ends in -o. Only four-form adjectives have separate masculine and feminine forms.

Forming the Plural

To make a four-form adjective plural, just add -s:

alto → altos / alta → altas
pequeño → pequeños / pequeña → pequeñas

Las casas pequeñas son más baratas.

Small houses are cheaper.

Compramos unos zapatos nuevos.

We bought (some) new shoes.

Agreement with Mixed Groups

When a group contains both masculine and feminine items, Spanish uses the masculine plural form.

Juan y María son simpáticos.

Juan and María are nice.

Even if there are ten women and one man, the masculine plural form wins. This is grammatical, not about importance.

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When you learn a new noun, always learn its gender with it. That way you'll know instantly whether to say bonito or bonita when you later want to describe it.

Pronunciation Notes

The final -o and -a vowels are always pronounced clearly. Don't swallow them the way English speakers sometimes do with unstressed vowels — Spanish vowels stay crisp and open regardless of position.

El gato negro duerme en el sillón rojo.

The black cat is sleeping on the red armchair.

A Quick Check

Try matching each adjective to the noun in your head:

el carro + rojo → un carro rojo
la mesa + blanco → una mesa blanca
los libros + nuevo → unos libros nuevos
las flores + amarillo → unas flores amarillas

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If the adjective ends in -o in its base form, you can always expect all four endings. If it doesn't end in -o, check whether it's a two-form adjective or an exception.