The Infinitive — Overview

The infinitive — infinitivo in Portuguese — is the base form of a verb: falar ("to speak"), comer ("to eat"), partir ("to leave"). It is the form you meet first when you pick up a dictionary, because every Portuguese verb is listed under its infinitive. But the infinitive is not only a reference form; it is also a fully working part of the language that shows up in modal constructions, after prepositions, as the subject of sentences, and in impersonal expressions. In Portuguese, it has one further surprise: it can be conjugated. While English, French, Italian, and Spanish all have a single, unchangeable infinitive, Portuguese has two infinitives — an invariant one and a personal, subject-marking one. Learning when to use each is one of the features that makes Portuguese grammar distinctive even among its Romance cousins.

This overview is the starting point. It explains what the infinitive is, where it appears, and how the two kinds of infinitive — impersonal and personal — divide the territory between them. Dedicated pages handle each use in detail.

What the infinitive is

The infinitive is the form of a verb that names the action without specifying who is doing it, when it happens, or how the speaker feels about it. In English, it is usually marked with "to" — to speak, to eat, to leave. In Portuguese, the infinitive is a single word, always ending in one of three vowels plus an -r:

These three endings define the three conjugation classes of Portuguese verbs. Every Portuguese verb belongs to one of them, and its pattern of conjugation (the endings in each tense) is determined by which class it falls into. See -ar, -er, -ir verbs for the details.

There is one important exception to the -ar / -er / -ir pattern: pôr ("to put") and its compounds (compor, repor, supor, propor, depor) end in -or and form a small fourth class all to themselves.

The impersonal infinitive

The most familiar infinitive is what grammars call the impersonal infinitive or simply "the infinitive" — the invariant dictionary form. It has no personal endings and does not change to match its subject. It is the infinitive you find in every other Romance language.

In all three of these sentences, the infinitive (aprender, estudar, ler) does not indicate who is doing the action. The subject is established elsewhere in the sentence or from context. This is exactly how the English infinitive works.

The personal infinitive — Portuguese's signature feature

Portuguese also has a second infinitive that does mark its subject. It is called the personal infinitive (infinitivo pessoal or infinitivo flexionado), and it is one of the grammatical features that makes Portuguese distinctive among Romance languages. Only Portuguese and Galician, with traces in Sardinian, preserve it in active use.

The personal infinitive looks identical to the impersonal in the 1sg and 3sg, but carries personal endings in the other forms:

In these three examples, the verb's ending itself tells you the subject — falarmos = "us (speaking)," chegares = "you (arriving)," entrarem = "they (entering)." No que clause is needed; no subjunctive mood has to be invoked. The infinitive does the job on its own.

For the full treatment — formation, uses, and the crucial question of when to pick personal over impersonal — see Personal Infinitive: Overview.

The seven main uses of the infinitive

Here is the map of where infinitives (both kinds) show up in Portuguese. Each of these is treated in more detail in a dedicated page.

1. As the dictionary form

Every Portuguese verb is listed under its infinitive. When you encounter a conjugated form — falávamos, comeu, partirão — the first step in looking it up is to identify the underlying infinitive: falar, comer, partir.

2. After modal and aspectual verbs

Verbs like poder ("can"), querer ("want to"), dever ("should"), saber ("know how to"), precisar de ("need to"), ter de / ter que ("have to"), and the aspectual auxiliary ir ("going to") take an infinitive complement.

In this construction, the infinitive is always impersonal — it takes no endings because the subject is already clear from the main verb's conjugation.

3. After prepositions

Portuguese uses the infinitive after prepositions where English often uses the -ing form (the gerund). De comer, para ver, sem dormir — in Portuguese these are infinitives, not participles.

When the subject of the infinitive after the preposition is different from the subject of the main verb, Portuguese uses the personal infinitive.

For the full treatment, see Personal Infinitive after Prepositions.

4. As the subject of a sentence

The infinitive can function as a noun, serving as the subject of a sentence — the way English uses the -ing form.

This is the impersonal infinitive — no specific subject is needed, because the action is being talked about in the abstract.

5. In impersonal expressions

Constructions like é importante, é preciso, é bom, é difícil, convém ("it is advisable to"), and vale a pena ("it's worth") take an infinitive complement. When the subject is generic, use the impersonal infinitive; when the subject is specific, use the personal infinitive.

See Personal Infinitive with Impersonal Expressions for the nuances of this choice.

6. In the periphrastic future

The construction ir + infinitive is the everyday way to express the future in both European and Brazilian Portuguese — similar to English "going to."

See ir + infinitive for the full pattern.

7. In periphrastic / aspectual constructions

Portuguese has a rich set of periphrastic verb constructions that combine an auxiliary with an infinitive to express aspect or nuance: estar a + infinitive (progressive), começar a + infinitive ("to start to"), acabar de + infinitive ("to have just"), voltar a + infinitive ("to do again"), costumar + infinitive ("to usually do"), and many more.

See the Periphrastic Constructions Overview for the full inventory.

Impersonal or personal — how do you choose?

This is the single biggest question the infinitive raises for learners, and the full answer is the subject of Personal vs Impersonal Infinitive. The quick version:

Use the impersonal infinitive when:

• The subject is the same as that of the main verb (Quero falar com ela — "I want to speak with her").
• The statement is generic or the subject is unspecified (Fumar é mau — "Smoking is bad").
• After modal verbs (posso falar, quero comer), because the subject is already clear.

Use the personal infinitive when:

• The subject of the infinitive is different from the subject of the main verb (É importante eles chegarem cedo — "It's important that they arrive early").
• You want to make the subject explicit and unambiguous, especially after prepositions (Antes de chegarmos, ligamos — "Before we arrive, we'll call").
• The subject is 2sg (tu), 1pl (nós), or 3pl (eles), where the personal ending makes a visible difference.

When the subject is 1sg (eu) or 3sg (ele), the personal and impersonal forms look identical, so the choice is invisible. The question only arises with tu, nós, and eles.

A note on the gerund and compound infinitives

Two related categories deserve a brief mention before we close, so you can see where the infinitive stops.

The gerund (gerúndio — falando, comendo, partindo) is a separate non-finite form that translates the English -ing. It is not an infinitive at all; it behaves differently and appears in different constructions. Don't confuse Fumar é mau ("smoking is bad" — infinitive as subject) with Estava a fumar (European Portuguese progressive, using the infinitive) or Estava fumando (Brazilian Portuguese, using the gerund). European Portuguese uses the gerund much less than Brazilian Portuguese does.

Compound infinitives express anteriority (an action completed before another): ter falado ("to have spoken"), ter comido ("to have eaten"), ter partido ("to have left"). These combine the infinitive of ter with a past participle, and they also have a personal form (teres falado, termos falado, terem falado).

Both the gerund and compound infinitives get their own treatment elsewhere in the grammar; flag them here as the neighbours of the plain infinitive.

The infinitive as a dictionary citation

One more practical note: when Portuguese speakers talk about verbs, they refer to them by the infinitive, just as English speakers refer to them by the to-form. If you ask "what does adormeci mean?", the answer will begin "adormecer is..." — bouncing you back to the infinitive as the reference point.

Common Mistakes

Key Takeaways

• The infinitive is the base, unconjugated form of a verb: falar, comer, partir. Every verb is listed in the dictionary under its infinitive.
• Portuguese verbs fall into three infinitive classes by their ending: -ar, -er, -ir, with a small fourth class in -or (essentially pôr and its compounds).
• Portuguese has two infinitives: the impersonal (invariant — falar) and the personal (conjugated for subject — falar, falares, falar, falarmos, falarem).
• The infinitive appears: as the dictionary form, after modals (poder, querer, dever), after prepositions (antes de, para, sem, depois de), as a subject (Fumar é mau), in impersonal expressions (É importante), in the periphrastic future (vou falar), and in aspectual constructions (estou a falar, acabei de falar).
• Rule of thumb: use the impersonal infinitive when the subject matches the main verb; use the personal infinitive when the subject is different or needs to be made explicit. The choice is only visible in tu, nós, and eles forms; eu and ele / ela look the same in both.
• The personal infinitive is Portuguese's signature grammatical feature and one of the things that makes the language distinct from its Romance cousins. Learning it well is a B1/B2 milestone.