Adjectives I

Adjectives are frequently descriptive. That is, most often adjectives are used to describe a noun, or distinguish the noun from a group of similar objects. For example, an adjective might describe the color of an object.
the red pen
the blue pen

In Spanish, most adjectives change form, depending upon whether the word they modify is masculine or feminine. Notice the difference between "the tall boy" and "the tall girl."
el chico alto
la chica alta

Adjectives also change form depending upon whether the word they modify is singular or plural. Notice the difference between "the tall boy" and "the tall boys" ; "the tall girl" and "the tall girls."
el chico alto
los chicos altos
la chica alta
las chicas altas

Many common adjectives end in -o. These adjectives have four forms. The following words all mean "tall":

The correct form of the adjective depends upon the noun it modifies. Is the noun masculine or feminine? Singular or plural?
libro rojo
red book
pluma roja
red pen
libros rojos
red books
plumas rojas
red pens

Notice how the endings of the nouns and these adjectives are similar.
libro rojo
pluma roja
libros rojos
plumas rojas

Adjectives that end in -e also change form for singular or plural. To form the plural, simply add -s.
la chica inteligente
las chicas inteligentes

Adjectives that end in -e do not, however, change form for masculine or feminine.
la chica inteligente
el chico inteligente
las chicas inteligentes
los chicos inteligentes

Similarly, most adjectives that end in a consonant do change form for singular or plural, but do not change for masculine or feminine. To form the plural, add -es.
la chica popular
el chico popular
las chicas populares
los chicos populares