Chapter 42 · B1

The Infinitive: Forms & Functions

Might help first: Ch. 20 — Verb Conjugation System: Overview & Regular Verbs, Ch. 30 — El Pretérito Perfecto (Present Perfect), Ch. 38 — El Presente de Subjuntivo: When to Use It (a suggestion, never a requirement)

The infinitive is the form of a Spanish verb you meet before any other — it’s the shape printed in the dictionary, the -ar/-er/-ir citation form every conjugation chart starts from. But in Spanish, the infinitive is far more than a lookup form you conjugate your way out of: it does real grammatical work on its own, standing in for an entire idea the way a noun does, gluing onto prepositions, and chaining onto other verbs with no conjugation at all. This chapter is the infinitive’s complete job description — where it goes, what follows it, and the one everyday choice (infinitive, or que plus subjunctive?) that trips up more English speakers than almost anything else in Spanish grammar.

Core Pattern: The Infinitive as a Verbal Noun

Fumar es malo: the infinitive standing in for a noun

In English, when you want to talk about an activity itself rather than someone doing it in the moment, you reach for “-ing”: “Smoking is bad for you.” “I love traveling.” Spanish has the identical job to fill, but hands it to a different form entirely — not the gerund (that restriction is Chapter 43’s whole subject, and it’s exactly why this chapter matters as much as it does), but the plain infinitive. Whenever a verb’s action itself is the subject or object of a sentence — the whole activity treated as a single “thing” — Spanish reaches for the infinitive, unconjugated and unchanged.

Fumar es malo para la salud.

Smoking is bad for your health.

Fumar, not fumando — this is Spanish's real equivalent of English's '-ing'-as-subject.

Nos encanta viajar.

We love traveling.

viajar is the object of encanta, functioning just like un libro would — a whole activity treated as one noun-like thing.

Ver es creer.

Seeing is believing.

Two bare infinitives working as subject and predicate at once — a tidy proverb built entirely on this pattern.

Hold onto this pattern: it’s the direct answer to a question English speakers instinctively ask — where’s Spanish’s “-ing”-as-subject? Right here, on the infinitive. Chapter 43 explains why the gerund, despite functioning as English’s “-ing” in other ways, is never allowed to do this particular job.

Building Out: Where the Infinitive Attaches

The infinitive-as-noun pattern above is really just one corner of a much bigger picture: Spanish infinitives attach constantly onto prepositions and onto other conjugated verbs, sometimes directly and sometimes through a linking preposition. All of it is governed by one shared fact — the second verb never conjugates.

After any preposition, the infinitive is the only option

Any time a preposition in Spanish is followed by a verb, that verb has to be an infinitive — no exceptions. This is a genuine trap for English speakers, because English usually reaches for “-ing” right after a preposition (“before leaving,” “without saying a word,” “for understanding grammar”) — a pattern Spanish never allows.

Antes de salir, cerré la puerta con llave.

Before leaving, I locked the door.

English: 'before leaving' (-ing). Spanish: antes de salir — always the infinitive after a preposition.

Sin decir nada, se marchó.

Without saying anything, he left.

Estudio español para entender mejor a mi familia.

I study Spanish to understand my family better.

para + infinitive expresses purpose — 'in order to.'

Straight after a conjugated verb: no preposition needed

A large family of common verbs — mostly verbs of wanting, ability, obligation, and opinion — attach directly to a following infinitive with no linking word at all.

Quiero comer algo antes de salir.

I want to eat something before leaving.

¿Sabes nadar?

Do you know how to swim?

saber + infinitive means 'to know how to' — a distinct meaning from poder, which is about ability or permission in the moment.

Debemos terminar el proyecto hoy.

We have to finish the project today.

Common verbs in this family include querer, poder, deber, necesitar, saber, soler, pensar (to intend), preferir, esperar, lograr, conseguir, intentar, and decidir.

Al + infinitive: a fixed formula for “upon doing something”

One preposition-plus-infinitive combination is common and specific enough to earn its own mention. Al + infinitive describes one action happening right as, or right before, another one — “upon doing,” “as soon as,” “when.” It’s a compact stand-in for a full cuando clause, usable with any verb.

Al llegar a casa, se quitó los zapatos.

Upon arriving home, he took off his shoes.

A tidy alternative to Cuando llegó a casa, se quitó los zapatos — same meaning, more compact.

Al oír la noticia, se puso a llorar.

Upon hearing the news, she started to cry.

A genuinely large list: which preposition goes with which verb

Beyond al, a long list of common verbs pair with a following infinitive through one specific linking preposition — a/de/en/con/por/para — and the preposition itself has to be learned verb by verb; there’s no shortcut rule that predicts which one a given verb takes. What follows isn’t exhaustive, but it covers the verbs you’ll run into constantly. (A future chapter on core prepositions will eventually index preposition-taking verbs more broadly; this list is scoped specifically to the ones that link to an infinitive.)

a — empezar a, comenzar a (to start doing), aprender a (to learn to), enseñar a (to teach someone to), ayudar a (to help to), atreverse a (to dare to), decidirse a (to make up one’s mind to), animarse a (to work up the enthusiasm to), invitar a (to invite someone to), volver a (to do again — full treatment in Chapter 45), ir a (near-future “going to” — full treatment in Chapter 45)
de — dejar de (to stop doing), tratar de (to try to), terminar de (to finish doing), acabar de (to have just done — full treatment in Chapter 45), olvidarse de (to forget to), acordarse de (to remember to), alegrarse de (to be glad to), tener ganas de (to feel like doing), encargarse de (to take charge of)
en — pensar en (to think about doing), quedar en (to agree to), insistir en (to insist on), tardar en (to take time to), consistir en (to consist of/in)
con — soñar con (to dream of), contar con (to count on), amenazar con (to threaten to)
por — luchar por (to fight to), esforzarse por (to make an effort to), preocuparse por (to worry about), optar por (to opt to)
para — prepararse para (to prepare to), servir para (to be used for)

Empezó a trabajar aquí el mes pasado.

He started working here last month.

Dejé de fumar hace un año.

I quit smoking a year ago.

dejar de + infinitive means 'to stop doing' — don't confuse it with dejar + infinitive without de, which means 'to let/allow' (see the exception verbs below).

Trato de entender la gramática, pero a veces es difícil.

I'm trying to understand the grammar, but sometimes it's hard.

¿Soñáis con viajar a Sudamérica algún día?

Do you all dream of traveling to South America someday?

Castellano vosotros form — soñáis, from soñar con + infinitive.

The perfect infinitive: haber + participle

The infinitive has a compound form too, built exactly like every other haber-based compound tense in this book: the invariant infinitive haber plus a past participle. Chapter 30 has the full irregular-participle list — nothing here is different from those same participles, just glued onto haber’s infinitive instead of a conjugated form.

Después de haber comido, salimos a caminar.

After having eaten, we went out for a walk.

Siento haber llegado tarde a la reunión.

I'm sorry for arriving late to the meeting.

Literally 'sorry to have arrived late' — the perfect infinitive marks that the lateness happened before the apology, not at the same time as it.

Gracias por haberme ayudado.

Thanks for helping me.

por + perfect infinitive — thanking someone for something already completed.

Nuance, Exceptions & Contrast

Infinitive vs. subjunctive: the same-subject rule, in full

Chapter 38 introduced this rule from the subjunctive’s side: que plus subjunctive only appears once a subordinate clause has picked up a subject of its own, different from the main clause’s subject. Seen from the infinitive’s side, it’s the same coin’s other face — whenever the person doing the wanting, hoping, or needing is the same person doing the second action, Spanish drops que and the subjunctive entirely and reaches for the plain infinitive instead. For the ordinary WEIRDO-trigger verbs, this holds with no exceptions:

Quiero comer.

I want to eat.

One subject (yo) — infinitive, no que, no subjunctive.

Quiero que comas.

I want you to eat.

Two subjects (yo wants, tú eats) — que plus subjunctive required.

Espero llegar a tiempo.

I hope to arrive on time.

Same subject throughout — infinitive.

Espero que llegues a tiempo.

I hope you arrive on time.

Different subject — que plus subjunctive.

The same logic governs impersonal expressions (es necesario, es importante, es bueno…): used as a general statement with no specific person in mind, they take a bare infinitive; the moment a specific subject enters the sentence, que plus subjunctive takes over.

Es importante estudiar.

It's important to study.

A general statement, true for anyone — infinitive.

Es importante que estudies.

It's important that you study.

Now about one specific person — que plus subjunctive.

The exception: a few verbs allow either pattern

A small, specific class of verbs breaks the pattern above in a genuinely useful way: verbs of permission and causation — dejar (to let), hacer (to make/cause), permitir (to permit), mandar (to order), prohibir (to forbid), invitar (to invite) — allow the infinitive construction even when the second subject is a different person. That second person simply shows up as an object pronoun instead of as the subject of a que-clause, so both patterns are grammatical side by side:

Le dejé salir.

I let him leave.

Infinitive pattern — the causee (him) surfaces as the object pronoun le, not as a subject.

Dejé que saliera.

I let him leave.

Que plus subjunctive pattern — exactly the same meaning, built the 'ordinary' way.

Mis padres me permitieron viajar solo.

My parents allowed me to travel alone.

Mis padres permitieron que viajara solo.

My parents allowed me to travel alone.

Same meaning as above, que-clause version.

Me hizo reír.

He made me laugh.

With hacer specifically, this infinitive pattern is overwhelmingly the natural everyday choice.

Bringing It Together

Antes de salir esta mañana, decidí dejar de posponer las cosas: quiero terminar el informe hoy. Mi jefe prefiere que lo entregue mañana, pero le dije que prefiero acabarlo ya. Después de haberlo enviado, podré descansar.

Before leaving this morning, I decided to stop putting things off: I want to finish the report today. My boss would rather I turn it in tomorrow, but I told him I'd rather finish it now. After having sent it, I'll be able to rest.

Every pattern from this chapter in one passage: after a preposition (antes de salir), dejar de + inf, a direct complement (quiero terminar), the same-subject infinitive (prefiero acabarlo) against the different-subject subjunctive (prefiere que lo entregue), and the perfect infinitive (después de haberlo enviado).

Faced with a second verb, work through it in order: is there a preposition immediately before it? Infinitive, always. Is it glued straight onto a verb like querer, poder, or deber? Infinitive, no preposition needed. Does the subject change between the two verbs? If so, check whether the main verb belongs to the small dejar/hacer/permitir/mandar/prohibir family — if it doesn’t, que plus subjunctive is required; if it does, either pattern works. And if the whole action happened before another point in time, haber plus participle turns any of the above into its perfect form.

Where to Go Next

Chapter 43, The Gerund: Forms & Functions — the flip side of this chapter’s opening section: why the gerund can’t do the noun job the infinitive just did, and what it does instead.
Chapter 38, El Presente de Subjuntivo: When to Use It — the WEIRDO framework and the subjunctive side of the same-subject rule detailed above.
Chapter 30, El Pretérito Perfecto (Present Perfect) — the full irregular past-participle list this chapter’s perfect infinitive reuses without re-deriving it.
Chapter 41, Conditional Sentences (Si Clauses) & Sequence of Tenses — the full si-clause system behind the literary de + perfect infinitive shortcut mentioned above.
Chapter 45, Verbal Periphrases (Perífrasis Verbales) — the true, full home for ir a, volver a, and acabar de, only indexed here as part of the linking-preposition list.

Ready to practice?

10 exercises · multiple-choice, fill-blank, error-correction…