The infinitive is the dictionary form of the verb — falar (to speak), comer (to eat), partir (to leave) — and in English that's the end of the story: "to speak" never changes. Portuguese is different in a way that has no parallel in English, Spanish, French, or Italian: it has two infinitives. There is the ordinary, unchanging one you'd expect, and there is a second infinitive that takes person endings, as if "to speak" could agree with "we" or "they." This page maps the whole system so you know what you're dealing with and where each piece is taught in depth.
Two infinitives, side by side
| Regular (impersonal) infinitive | Personal (inflected) infinitive | |
|---|---|---|
| Form | One fixed form: falar | Changes with person: falar, falarmos, falarem |
| Has a subject? | No subject of its own | Carries its own subject |
| Typical use | After modals, after prepositions with no new subject, as a noun | When the infinitive clause has a different subject from the main verb |
| English analogue | "to speak" | "for us to speak" — but Portuguese marks it on the verb itself |
The forms only visibly differ in the we and they persons. In the singular, the regular and personal infinitives look identical — falar is falar either way. That's why beginners use the personal infinitive correctly for ages without realizing it exists: it only shows its hand in the plural.
The regular (impersonal) infinitive
This is the one you already know. It never changes, and it shows up in the same places an English "to + verb" or "-ing" form would.
After a modal or auxiliary verb:
Eu quero comer alguma coisa antes de sair.
I want to eat something before leaving.
Você pode me ajudar com isso?
Can you help me with this?
After a preposition, when there's no new subject:
Ele saiu sem falar com ninguém.
He left without speaking to anyone.
As a noun (the subject of a sentence):
Fumar faz mal à saúde.
Smoking is bad for your health.
The full inventory of uses — modals, prepositions, recipes and instructions, the infinitive-as-noun, and the bare-infinitive pattern that surprises Spanish speakers — is on The Regular (Impersonal) Infinitive.
The personal infinitive
Here is the feature that makes Portuguese famous among linguists. The personal infinitive is an infinitive that agrees with a subject. You use it when the infinitive's subject is different from — or needs to be stated separately from — the main verb's subject.
É importante chegarmos cedo amanhã.
It's important that we arrive early tomorrow.
That chegarmos is the personal infinitive of chegar, marked for we. Compare the singular, where you can't see the inflection:
É importante chegar cedo amanhã.
It's important to arrive early tomorrow. (general / no specific subject)
The personal infinitive shines after prepositions and conjunctions when the clause has its own subject:
Antes de eles chegarem, eu já tinha arrumado tudo.
Before they arrived, I had already tidied everything up.
O professor falou alto para todos entenderem.
The teacher spoke loudly so that everyone would understand.
In both, the infinitive carries the subject of its own little clause (eles, todos) and inflects to match it (chegarem, entenderem). Full details, including the prepositional and subjunctive-replacing uses, are on The Personal Infinitive: Overview, and how to build the forms is on Forming the Personal Infinitive.
Why Portuguese alone has this
Every Romance language inherited the Latin infinitive, but only Portuguese kept (or developed) a fully productive inflected one. Spanish, French, and Italian all lost it. Where Spanish must say para que lleguemos temprano (with a subjunctive in a full subordinate clause) or antes de que ellos lleguen, Portuguese can keep the lighter infinitive and simply inflect it: para chegarmos cedo, antes de eles chegarem. This is genuinely unique — it's not a feature you can transfer from any other language you might know.
How to tell which one you need
The decision is almost always about the subject:
- Same subject as the main verb, or no subject at all? Use the regular infinitive. Quero sair (I want to leave — same subject: I want, I leave).
- A different or explicitly stated subject? Reach for the personal infinitive. Quero que vocês saiam would use a subjunctive, but É melhor saírem agora (it's better for you all to leave now) uses the personal infinitive.
Preciso estudar mais.
I need to study more. (one subject — regular infinitive)
É melhor estudarmos juntos.
It's better for us to study together. (the clause has its own subject 'we' — personal infinitive)
A dedicated decision guide lives at Personal vs Impersonal Infinitive.
Common Mistakes
These are the errors that come straight from English having only one, unchanging infinitive.
❌ É importante para nós chegar cedo.
Understandable but unnatural — with an explicit plural subject, Brazilians inflect the infinitive.
✅ É importante chegarmos cedo.
It's important that we arrive early. (personal infinitive carries the 'we')
❌ Antes de eles chegar, eu saí.
Incorrect — with the subject 'eles' the infinitive must inflect to the 'they' form.
✅ Antes de eles chegarem, eu saí.
Before they arrived, I left.
❌ Eu quero a comer agora.
Incorrect — Portuguese uses a bare infinitive after a modal; there's no 'a' (unlike Spanish 'voy a comer').
✅ Eu quero comer agora.
I want to eat now.
❌ Para nós falarem português, precisamos praticar.
Incorrect — the subject is 'nós' (we), so it must be 'falarmos', not the 'they' form.
✅ Para nós falarmos português, precisamos praticar.
For us to speak Portuguese, we need to practice.
Key Takeaways
- Portuguese has two infinitives: the regular (unchanging) one and a personal one that takes person endings.
- They differ visibly only in the we (-mos) and they (-em) forms; the singular forms are identical.
- Use the regular infinitive after modals, after prepositions with no new subject, and as a noun.
- Use the personal infinitive when the infinitive clause has its own, separately stated subject.
- This personal infinitive is unique to Portuguese among the major Romance languages — knowing it is what separates an intermediate speaker from a beginner.
Now practice Portuguese
Reading grammar gets you part of the way. The exercises are where it sticks — free, no signup needed.
Start learning Portuguese→Related Topics
- The Regular (Impersonal) InfinitiveA1 — The unchanging dictionary form of the verb — falar, comer, partir — and the five main places it appears in Brazilian Portuguese.
- The Personal Infinitive: OverviewB1 — Portuguese's signature feature — an infinitive that carries person and number endings, letting infinitive clauses take their own subject.
- Forming the Personal InfinitiveB1 — How to build the personal infinitive — the infinitive plus uniform person endings — and why even irregular verbs are perfectly regular here.
- Verb Moods: Indicative, Subjunctive, ImperativeA2 — An overview of the three Brazilian Portuguese verb moods — and why the subjunctive, nearly dead in English, is alive and obligatory in everyday Brazilian speech.
- Personal vs Impersonal InfinitiveB1 — How to decide whether to leave the infinitive bare or inflect it for person — the rule turns on whether the infinitive has its own, distinct subject.