Personal vs Impersonal Infinitive

Portuguese has something no other major Romance language has and English cannot imitate: an infinitive that can be conjugated. Beside the plain dictionary form falar ("to speak"), Portuguese can build falarmos ("for us to speak"), falarem ("for them to speak"). The hard part is not forming it — the endings are regular and predictable — but deciding when to reach for it instead of the bare infinitive. This page is a decision guide: one question resolves the vast majority of cases. For the full paradigm and the finer syntactic environments, see the Personal Infinitive overview.

The one question that decides it

Ask: does the infinitive have its own subject, different from (or more explicit than) the subject of the main verb?

• No → use the impersonal (bare) infinitive: falar, comer, partir.
• Yes → use the personal (inflected) infinitive: falarmos, comerem, partires.

That is the whole rule. The inflection (-es, -mos, -em) exists for one job: to flag whose action the infinitive describes when that information would otherwise be lost.

When the action has no specific subject

If the infinitive expresses a general truth, a piece of advice to nobody in particular, or an action whose doer is "anyone / people," there is no subject to mark. Stay bare.

Here English uses either "to + verb" or the -ing gerund, and Portuguese answers with the bare infinitive. There is simply no one to inflect for.

When the subject is the same as the main verb

If the same person does both actions — the subject of the main clause is also the doer of the infinitive — Portuguese leaves the infinitive bare. The subject is already stated once; repeating it on the infinitive would be redundant.

Notice antes de sair: even after a preposition, when the doer is the same as the main clause, you keep the bare infinitive. The temptation to inflect is strong here — resist it unless the subject changes.

When the infinitive has its own, different subject

This is where you inflect. The moment the infinitive describes a different person, or you want to make the subject explicit, the personal infinitive earns its keep — the ending tells the listener who.

Compare the minimal pair. With the same subject, bare; with a new subject, inflected:

The second sentence is impossible in Spanish or French, which would force a full subordinate clause with a conjugated verb (sin que los niños hicieran ruido). Portuguese compresses it: it just inflects the infinitive and keeps the lightness of an infinitive phrase.

The forms (regular and predictable)

The personal infinitive is built on the whole infinitive, not on a stem — that is why it is so easy. Take the dictionary form and add the endings:

The crucial consequence: a sentence like É bom estudarmos juntos shows the inflection (-mos) and instantly tells you the subject is nós — even though no pronoun appears. That is the personal infinitive doing pro-drop's work for it.

After prepositions: the most common trigger

Prepositional phrases (antes de, depois de, por, para, sem, até) are where the personal infinitive shows up most in real speech, precisely because they so often introduce a new subject.

In each, the inflection marks a subject distinct from the main clause, sparing you a heavier para que + subjunctive clause. In fact the personal infinitive is often a lighter alternative to the subjunctive — para nós entendermos instead of para que nós entendamos. See Personal Infinitive Replacing Subjunctive Clauses for when each is preferred.

The English speaker's mental shift

English has no inflected infinitive. The nearest thing is "for us to + verb": "It's important for us to leave." But that "for...to" is a fixed scaffold; the verb itself never changes shape. Portuguese drops the scaffold and instead bends the verb: é importante sairmos. The information English carries in the words "for us" is carried in Portuguese by the ending -mos.

This is why translating word-for-word leads English speakers astray in both directions: they either fail to inflect when a new subject appears (leaving the sentence ambiguous), or they over-inflect when the subject is the same and the bare form was correct.

Common Mistakes

Key Takeaways

• Ask one question: does the infinitive have its own, distinct subject? If yes, inflect; if no, leave it bare.
• General truths ("smoking is bad") and same-subject actions ("I want to leave") take the bare infinitive.
• A different or explicit subject — especially after prepositions like antes de, para, sem — triggers the inflected form (-mos, -em, -es).
• The inflection is a labeling device: it tells the listener whose action it is, which is exactly what English encodes with the clumsier "for...to."
• The forms are fully regular: add the endings to the whole infinitive. Only the plural and tu forms actually change spelling.