In Spanish, five parts of speech, commonly referred to as classes of words (clases de palabras), accept grammatical properties, such as gender, tense, number, person, case, mood, aspect, and degree, to relate to other words in a sentence. The classes of words that accept grammatical properties are pronouns (pronombres), verbs (verbos), adjectives (adjetivos), articles (artículos), and nouns (sustantivos), and the ones that do not are adverbs (adverbios), prepositions (preposiciones), conjunctions (conjunciones), and interjections (interjecciones).

	Gender	Tense	Number	Person	Case	Mood	Aspect	Degree
Verb		Yes	Yes	Yes		Yes	Yes
Pronoun	Yes		Yes	Yes	Yes
Adjective	Yes		Yes					Yes
Article	Yes		Yes
Noun	Yes		Yes

Verbs

Verbs in Spanish do the same in English: they express the states of being, actions, or processes of their subjects. To accomplish this dynamism, verbs accept the following grammatical properties.

Pronouns

Like in English, pronouns in Spanish are used to refer to people, animals, or things without having to name them. In Spanish, pronouns are subject to two types of classification; historically, Spanish traditional grammar classified them similarly to English traditional grammar, but in modern times, descriptive grammarians classify them differently. Pronouns accept the grammatical properties of gender, number, case, and person.

Adjectives

Just like in English, adjectives in Spanish modify nouns or pronouns. But in Spanish, adjectives must agree in gender and number with the nouns or pronouns they modify. Additionally, the adjectives that can express qualities in larger or smaller degrees—the grammatical property of degree—are called gradable (graduables); the adjectives that do not accept this property are called nongradable (no graduables).

Articles

In Spanish, articles function similarly to how they do in English in the sense that they determine whether a noun or noun phrase is definite or indefinite. But unlike in English, where articles are considered a subclass of adjectives, articles in Spanish constitute a separate category of classes of words. Like adjectives, articles must agree in gender and number with the nouns or pronouns they modify.

Nouns

Nouns in Spanish accept the grammatical property of number and function similarly to how they do in English, i.e., refer to an entity, quality, state, action, or concept, but in Spanish, this class of words determines the gender not only of the pronouns that refer to it but also of the articles and adjectives that modify it in a sentence. Furthermore, nouns are classified according to their gender attributes.

Adverbs

Like in English, adverbs in Spanish modify verbs, adjectives, and other adverbs. But in Spanish, they can also have an effect on nouns, pronouns, prepositions, and even entire sentences. Adverbs in Spanish are an invariable class of words—they do not accept grammatical properties—unlike in English, where they do accept the grammatical property of degree. Take note that some adverbs in Spanish appear to function as adjectives and so the grammatical properties of number and gender are incorrectly applied to them.

Prepositions

Like in English, prepositions in Spanish are an invariable class of words—they do not accept grammatical properties—that establish a relation between two elements, i.e., the object of the preposition (término), which generally is a noun or clause, and some other part of the sentence. And like in English, the preposition along with its object form prepositional phrases (grupos preposicionales).

Conjunctions

Like in English, conjunctions in Spanish are an invariable class of words—they do not accept grammatical properties—used not only to join words, groups, and sentences but also to establish a relationship of coordination or subordination between these elements.

Interjections

Like in English, interjections in Spanish are an invariable class of words—they do not accept grammatical properties—used to express feelings or impressions and to incite or induce people to act. When written in Spanish, interjections are used with exclamation points or question marks to emphasize their intrinsic intonation.