The Infinitive: Overview

The infinitive (el infinitivo) is the base form of a Spanish verb — the form you find when you look a verb up in the dictionary. Every Spanish infinitive ends in one of three sets of letters: -ar, -er, or -ir. These endings tell you which conjugation the verb belongs to, and they are the starting point for forming every tense.

Unlike conjugated forms, the infinitive is uninflected: it does not change for person, number, or tense. Hablar always means "to speak," whether the speaker is yo, nosotros, or ellos.

The three endings

Spanish verbs fall into three groups based on the last two letters of the infinitive. Each group follows its own pattern of endings when conjugated.

When to use the infinitive

The infinitive shows up in many situations where English might use either to + verb or a gerund (-ing). Here are the most common uses:

• After another conjugated verb, often a modal: Puedo ir. ("I can go.")
• After a preposition: antes de salir ("before leaving"). In English this slot usually takes -ing, but Spanish always uses the infinitive.
• As a noun, sometimes with the article el: El fumar es malo. ("Smoking is bad.")
• In impersonal instructions and signs: No fumar. ("No smoking.")
• After al to mean "upon doing something": Al entrar, lo vi. ("Upon entering, I saw him.")

The infinitive vs. the gerund

One of the most common mistakes English speakers make is using the gerund (-ando / -iendo) where Spanish requires the infinitive. In English, the gerund doubles as a noun ("Smoking is bad," "I like reading"), but in Spanish, that noun-like job belongs to the infinitive.

Infinitive in this guide

The following pages break down each major use of the infinitive in detail:

• Infinitive after prepositions
• Infinitive after verbs (no preposition)
• Verbs + a
  • infinitive
• Verbs + de
  • infinitive
• Verbs + en
  • infinitive
• Verbs + con / por
  • infinitive
• Al
  • infinitive
• Infinitive as a noun

Why it matters

Because the infinitive is the key to every tense, recognizing it — and knowing which preposition, if any, introduces it — is one of the most useful skills you can build early on. Many verbs require a specific preposition before an infinitive (ayudar a, tratar de, insistir en), and memorizing those pairings is just as important as learning conjugations.