Spanish/Adjectives

The Spanish language uses adjectives in a similar way to English and most other Indo-European languages. Spanish adjectives usually go after the noun they modify, and they agree with what they refer to in terms of both number (singular/plural) and gender (masculine/feminine). Spanish adjectives are very similar to nouns, and often interchangeable with them. A bare adjective can take an article and be used in the same place as a noun (where English would require nominalization using the pronoun one(s)). For example:

El rojo va aquí/acá, ¿no? = "The red one goes here, doesn't it?"
Hay que tirar las estropeadas = "We have to throw away the broken ones."

Agreement

Adjectives in Spanish can mostly be divided into two large groups: those that can be found in the dictionary ending in o, and the others. The former typically agree for number and gender; the latter typically agree just for number. Here are some examples: Frío means "cold". This is the dictionary form, and it corresponds to the masculine singular form. When it agrees with a feminine noun, it becomes fría. When it agrees with a plural noun, it becomes fríos. When it agrees with a noun which is both feminine and plural, it becomes frías. Here is a list of a few common adjectives in their four forms:

Frío = "cold"; → frío, fría, fríos, frías
Pequeño = "small"; → pequeño, pequeña, pequeños, pequeñas
Rojo = "red"; → rojo, roja, rojos, rojas
Here are a few common adjectives that agree only in number:
Caliente = "hot" → caliente, caliente, calientes, calientes
Formal = "formal" → formal, formal, formales, formales
Verde = "green" → verde, verde, verdes, verdes

The division into these two groups is a generalisation however. There are many examples such as the adjective español itself which does not end in o but nevertheless adds an a for the feminine and has four forms (español, española, españoles, españolas). There are also adjectives that do not agree at all (generally words borrowed from other languages, such as the French beige (also Hispanicised to beis)).

Descriptive and attributive uses

The superlative

Instead of putting muy, "very" before an adjective, one can use a special form called the superlative to intensify an idea. This consists of the suffix -ísimo.

Regular forms

muy rápido → rapidísimo
muy guapas → guapísimas
muy rica → riquísima
muy lento → lentísimo
muy duro → durísimo

Irregular forms

muy antiguo → antiquísimo
muy cursi → cursilísimo
muy inferior → ínfimo
muy joven → jovencísimo
muy superior → supremo
muy bueno → óptimo
muy malo → pésimo
muy grande → máximo¹
muy pequeño → mínimo¹

¹These two forms keep the original meaning of the superlative: not "very" but "the most".

Forms that are irregular in high literary style, and regular normally

muy amigo → amicísimo / amiguísimo
muy áspero → aspérrimo / asperísimo
muy benévolo → benevolentísimo / not used
muy célebre → celebérrimo / not used
muy cruel → crudelísimo / cruelísimo
muy fácil → facílimo / facilísimo
muy fiel → fidelísimo / fielísimo
muy frío → frigidísimo / friísimo
muy íntegro → integérrimo / integrísimo
muy libre → libérrimo / librísimo (familiar)
muy magnífico → magnificentísimo / not used
muy mísero → misérrimo / not used
muy munífico → munificentísimo / not used
muy pobre → paupérrimo / pobrísimo
muy sabio → sapientísimo / not used
muy sagrado → sacratísimo / not used

Forms that are not felt a superlative anymore

muy agrio ("very bitter") → acérrimo ("strong, zealous, fanatic")

Applying -ísimo to nouns is not frequent, but there is the famous case of Generalísimo. As in English and other languages influenced by it, a teenspeak superlative can be formed by the prefix super-, or sometimes hiper-, ultra-, re- or requete-. They can also be written as adverbs separate from the word.

Superlargo or súper largo = "super-long", "way long"
Requeteguay = "totally cool"