The infinitive is the base form of the verb. It does not change to mark person or number, so it does not say I, you, or they. It names the action, the state, or the change in a general way: to sing, to eat, to live, to be, to be, to go. In Spanish it appears as the form used to name the verb in the dictionary and also as the starting point for building other verb forms. In relation to other parts of the sentence, the infinitive preserves its verbal value because it can take complements: to read a book, to leave early, to be hungry. In grammatical texts it is also related to Verbal Gerunds and Verbal Participles, which are other non-personal forms of the verb.

Regular Spanish infinitives end in three groups: -ar, -er, and -ir. That ending shows the verbal class to which each verb belongs. Hablar, cantar, and trabajar are -ar verbs; comer, beber, and temer are -er verbs; vivir, escribir, and abrir are -ir verbs. The end of the infinitive lets you immediately recognize which conjugation model the verb will follow. That classification also helps when studying Periphrastic Verbs, because the infinitive at the end preserves the identity of the main verb.

Basic infinitive endings

Idea
Verbs in -ar form a regular infinitive that usually belongs to the first conjugation
Verbs in -er form a regular infinitive that usually belongs to the second conjugation
Verbs in -ir form a regular infinitive that usually belongs to the third conjugation

Some very frequent infinitives do not follow the regular pattern expected or show an irregular stem from this form. Ir and ser have short and very old infinitives, without the regular ending of a common family. Ver is also irregular because of its short form. Poder and tener preserve a stem that is widely used across conjugation, and their derivatives follow that same pattern: poder, podré, puedo; tener, tendré, tengo. Other everyday infinitives show irregularity in the base form or in the family they form, such as caber, haber, venir, poner, and salir. Early recognition of these verbs makes working with Modal Verbs easier, where poder, deber and querer appear very frequently.

Very common irregular infinitives

Idea
Some verbs have an infinitive that does not follow the regular pattern
Some frequent infinitives completely change their base form
Other common infinitives retain a short and very frequently used form
Certain infinitives very commonly express ability or possibility
Other infinitives indicate possession or necessity in a very common way

The infinitive can function as a noun and take the place of a name in the sentence. In this use it typically appears with determiners: el comer, el dormir, el estudiar. It can also go with prepositions or adjectives that normally accompany a noun: el comer rápido, el dormir temprano, lo mejor es estudiar. In this case, the infinitive names the action as an activity, not as a conjugated verb in a concrete situation. That is why it can appear in titles, instructions, and general expressions: El cantar de los pájaros, El vivir en la ciudad, El leer abre puertas.

Nominal uses of the infinitive

Usage	Explanation
Name of an action	We use the infinitive as a noun when we want to name an action in general
Subject of an activity	We use the infinitive as a central idea when we talk about an activity without specifying who does it
Abstract habit or pleasure	We use the infinitive as an abstract noun to talk about tastes or customs

After a preposition the infinitive is used, not a conjugated form. With para it expresses purpose: para estudiar, para comer, para salir temprano. With sin it indicates absence of an action: sin dormir, sin decir nada, sin mirar atrás. With por the infinitive appears in expressions of cause, exchange, or before a pending action: por venir, por hacer, por resolver. With antes de the infinitive is also used: antes de salir, antes de llamar, antes de empezar. The preposition connects directly to the non-personal verb form, and this construction is very common together with Periphrastic Verbs and with infinitives that function as the nucleus of the action.

Infinitive after a preposition

Usage	Explanation
Purpose	After for we use the infinitive to indicate an objective
Absence of action	After without we use the infinitive to express that something does not happen
Reason or prior step	After for we use the infinitive when the action functions as a cause or prior step
Earlier time	After before we use the infinitive to place a prior action

Many verbs introduce another verb in the infinitive to express modality. Querer + infinitive expresses desire or intent: quiero viajar. Poder + infinitive expresses ability or possibility: puedo ayudarte. Deber + infinitive expresses obligation or strong recommendation: debes estudiar. Soler + infinitive expresses habit: suelo desayunar temprano. In all these constructions, the first verb is conjugated and the second remains in the infinitive. The verb in the infinitive provides the main action, while the preceding verb conveys the idea of desire, possibility, obligation, or habit. This structure is studied in detail in Modal Verbs.

Infinitive with common modal verbs

Usage	Explanation
Desire	We use the infinitive after to want to express what someone wishes to do
Possibility	We use the infinitive after can to express ability or possibility
Obligation	We use the infinitive after must to express necessity or a rule
Habit	We use the infinitive after usually to talk about frequent habits

Many common Spanish expressions are formed with a conjugated verb + infinitive. In voy a comer, va a llover, or vamos a empezar, the verb ir conveys the idea of near-future or intention and the infinitive presents the main action. In tener que estudiar, tengo que llamar, or tienen que salir, the verb tener introduces obligation. Other very common constructions are hay que trabajar, deber de ser and estar por hacer, where the first verb functions as support and the infinitive preserves the central meaning. The complete set is called a verbal periphrasis and is studied in Periphrastic Verbs.

Common periphrastic constructions with the infinitive

Usage	Explanation
Imminent action	We use to be going to with the infinitive to talk about an action that is very close in time
Necessity	We use to have to with the infinitive to express obligation or necessity
Beginning of an action	We use to begin to with the infinitive to indicate that an action begins

With the infinitive, pronouns can go in front of the verb or attached to the end. You say quiero verlo or lo quiero ver; vamos a hacerlo or lo vamos a hacer. When the infinitive is joined to another verb, the usual thing is to place the pronoun in front of the conjugated verb or attached to the infinitive. In rapid speech and natural style, the joined form appears very frequently: decírselo, ayudarme, comprártelo. If there are two pronouns, the order is kept: first the indirect object and then the direct object: voy a dárselo, quiero enviártela. The infinitive allows that union because it preserves its non-personal form.

Placement of pronouns with the infinitive

Idea
With the infinitive, the pronoun can go before it or joined to the end
When the pronoun is joined to the infinitive, it forms a single word
In rapid speech, the form attached to the infinitive is usually preferred

Reflexive infinitives carry a pronoun attached at the end: lavarse, peinarse, sentarse, levantarse, despertarse. The action falls on the same person who performs it, even though the verb remains in the infinitive. There is also the compound infinitive haber + participle, which places the action before another reference: haber comido, haber salido, haber terminado. This form appears in expressions like después de haber llegado or sin haber estudiado. The compound infinitive connects with Verbal Participles, because its second part is the participle of the main verb.

Reflexive and compound forms of the infinitive

Idea
Reflexive infinitives carry a pronoun showing that the action falls on the same person
Reflexive infinitives can express very natural everyday actions
The compound infinitive uses to have plus a participle to talk about an earlier action