Personal Infinitive Errors | Portuguese (Brazil) Grammar

The personal infinitive (infinitivo pessoal) is one of the few genuinely Portuguese-specific features with no real equivalent in English, Spanish, or French. It is an infinitive — a to do form — that nonetheless inflects for its own subject. English has nothing like it: the closest we get is the awkward "for us to go," where the subject sits outside the verb. In Portuguese the subject information is baked into the verb ending itself: para irmos (for us to go), para irem (for them to go).

Because English gives you no template, the errors here are about recognition, not formation. The dominant mistake is under-use: you don't deploy it where it belongs because your English brain never reaches for it. A smaller set of mistakes is over-use (inflecting an infinitive that should stay impersonal) and confusion with the subjunctive. This page sorts them out.

The endings: how the personal infinitive inflects

Start from the plain (impersonal) infinitive and add personal endings. For all conjugations the pattern is the same, built on the infinitive itself:

Subject	Ending	falar	comer	partir
eu	— (bare)	falar	comer	partir
você / ele / ela	— (bare)	falar	comer	partir
nós	-mos	falarmos	comermos	partirmos
vocês / eles / elas	-em	falarem	comerem	partirem

In the European paradigm there is also a -es ending for tu (falares), but Brazilian Portuguese rarely uses tu with its proper verb forms, so in practice the BR personal infinitive shows up mainly in the nós (-mos) and eles/vocês (-em) persons — exactly the persons where it visibly differs from the bare infinitive and therefore matters. A crucial subtlety: regular verbs' personal infinitive is identical to the future subjunctive (falarmos, falarem), but irregular verbs differ (personal infinitive sermos, serem vs future subjunctive formos, forem). Don't conflate the two paradigms.

Error 1: under-use after prepositions

The most frequent failure. After prepositions like para, antes de, depois de, sem, até, when the subordinate verb has its own explicit or implied subject, you should inflect the infinitive to show that subject. Learners leave it bare because English would.

❌ É importante para nós estudar muito antes da prova.

Incorrect — the infinitive has its own subject ('nós'), so it must inflect: 'estudarmos'.

✅ É importante estudarmos muito antes da prova.

It's important that we study a lot before the test.

❌ Antes de nós sair, fecha a janela.

Incorrect — inflect for 'nós': 'sairmos'.

✅ Antes de nós sairmos, fecha a janela.

Before we leave, close the window. (informal)

The personal infinitive lets you keep an infinitive (lighter, less clausal) instead of opening a full subjunctive clause, while still marking who does the action. That is its whole point: subject-marking without a finite que-clause.

✅ Trouxe um casaco para vocês não passarem frio.

I brought a coat so you all wouldn't be cold.

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Trigger to watch for: a preposition (para, antes de, depois de, sem, até, por) followed by an action whose doer is plural and different from the main subject. That is where BR speakers reach for -mos / -em. Para fazermos, sem eles saberem, depois de chegarmos.

Error 2: "é melhor / é hora de" with a plural subject

A natural, high-frequency place the personal infinitive surfaces — and where learners flatten it.

❌ É melhor vocês ir agora, o trânsito vai piorar.

Incorrect — plural subject 'vocês' triggers 'irem'.

✅ É melhor vocês irem agora, o trânsito vai piorar.

You'd better go now, traffic is going to get worse.

✅ Já é hora de eles assumirem a responsabilidade.

It's time for them to take responsibility.

Error 3: over-use — inflecting an impersonal infinitive

The opposite mistake, common in learners who have just discovered the feature and start inflecting everything. When the infinitive is truly impersonal — a general statement with no specific subject — it stays bare. And critically, when the infinitive shares its subject with the main verb (no subject change), you also use the bare infinitive.

❌ Fumar fazerem mal à saúde.

Incorrect — a general truth with no subject; the infinitive stays bare: 'Fumar faz mal'.

✅ Fumar faz mal à saúde.

Smoking is bad for your health.

❌ Nós queremos estudarmos mais.

Incorrect — same subject as the main verb, so the infinitive stays bare.

✅ Nós queremos estudar mais.

We want to study more.

That second one is the key insight: after a modal/auxiliary-type verb (querer, poder, dever, precisar, ir) where the doer doesn't change, you do not inflect — queremos estudar, never queremos estudarmos. The personal infinitive earns its inflection only when there is a genuine, distinct subject for the infinitive clause.

Error 4: confusing it with the subjunctive

The personal infinitive and a subjunctive que-clause often express the same idea through different machinery, and both can be correct. Learners sometimes think one is "wrong"; usually neither is — they are stylistic alternatives.

✅ Comprei isso para fazermos um bolo juntos.

I bought this so we could make a cake together. (personal infinitive)

✅ Comprei isso para que façamos um bolo juntos.

I bought this so that we make a cake together. (subjunctive, slightly more formal)

The personal-infinitive version (para fazermos) is lighter and far more common in everyday Brazilian speech. The para que + subjunctive version (para que façamos) is grammatical but feels more formal/written. The error is not choosing one — it is mixing them, e.g. para que fazermos (❌), which jams a subjunctive conjunction onto an infinitive.

❌ Comprei isso para que fazermos um bolo.

Incorrect — 'para que' requires a finite subjunctive ('façamos'), not an infinitive.

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Decision shortcut: if there's a que, you need a finite verb (subjunctive). If there's no que — just a preposition like para, antes de — and the subject is its own, use the personal infinitive. Never both.

Error 5: forgetting it after perception and causative verbs

With perception verbs (ver, ouvir) and causatives (deixar, mandar, fazer), a plural subject can also trigger the personal infinitive — though here the bare infinitive is often acceptable too, so this is the softest of the errors.

✅ Ouvi os vizinhos discutirem a noite toda.

I heard the neighbors arguing all night.

✅ Deixa as crianças brincarem mais um pouco.

Let the kids play a little longer. (informal)

Summary and recap

The personal infinitive has no English scaffolding, so build the recognition habit deliberately:

Form it from the bare infinitive: add -mos for nós and -em for vocês/eles. (Regular verbs match the future subjunctive; irregular verbs do not.)
Use it when an infinitive clause has its own, distinct subject, especially after a preposition (para fazermos, antes de saírem) or an impersonal expression (é melhor vocês irem).
Don't inflect when the infinitive is impersonal/general (Fumar faz mal) or shares the main verb's subject (queremos estudar, not estudarmos).
Don't mix it with the subjunctive: para fazermos OR para que façamos, never para que fazermos.

The unifying question to ask yourself: Does this infinitive clause have a subject of its own that's different from the main verb's? If yes, and especially if it's plural, inflect. If no, leave it bare. That single test resolves nearly every error on this page.

Common Mistakes

❌ Antes de eles chegar, arruma a sala.

Incorrect — plural subject 'eles' triggers 'chegarem'.

✅ Antes de eles chegarem, arruma a sala.

Before they arrive, tidy up the living room. (informal)

❌ Trouxe documentos para nós assinar.

Incorrect — own subject 'nós' triggers 'assinarmos'.

✅ Trouxe documentos para nós assinarmos.

I brought documents for us to sign.

❌ Vamos podermos terminar isso hoje.

Incorrect — same subject as 'vamos', so stay bare: 'poder'.

✅ Vamos poder terminar isso hoje.

We're going to be able to finish this today.

❌ Estudar muito serem importante.

Incorrect — impersonal general statement stays bare.

✅ Estudar muito é importante.

Studying a lot is important.

❌ É bom vocês descansar antes da viagem.

Incorrect — plural subject triggers 'descansarem'.

✅ É bom vocês descansarem antes da viagem.

It's good for you all to rest before the trip.

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