What is the personal infinitive in Portuguese?
Portuguese has an infinitive that conjugates for person — falar, falares, falar, falarmos, falarem. No other Romance language has it. It lets you attach a subject to an infinitive clause without needing a subordinate clause, and it often replaces a subjunctive construction with something shorter and more natural.
An infinitive with endings
The forms are built on the plain infinitive: add -es for tu, -mos for nós, -em for eles, and leave the eu and ele forms bare. For regular verbs it is identical to the future subjunctive, which is why the two are often confused.
para eu falar
for me to speak
para tu falares
for you to speak
para nós falarmos
for us to speak
para eles falarem
for them to speak
It removes the need for a subordinate clause
Where Spanish or French would need que plus a subjunctive, Portuguese can often use the personal infinitive instead. The result is shorter, and in many contexts it is what a native speaker would actually say.
É melhor tu ires embora.
It's better for you to leave.
Rather than é melhor que tu vás.
Antes de saírem, fechem a porta.
Before you leave, close the door.
Obrigado por virem.
Thank you for coming.
The -em marks that it was them who came.
It disambiguates who is doing what
This is where it earns its keep. A plain infinitive leaves the subject unstated; the personal infinitive states it in the ending, so a sentence that would be ambiguous in Spanish is clear in Portuguese.
É difícil compreender.
It's hard to understand.
Subject unspecified.
É difícil compreendermos.
It's hard for us to understand.
The ending names us.
Common mistakes
Obrigado por vir. (thanking several people)
Obrigado por virem.
The ending marks who came. Addressing a group needs the -em form.
Antes de nós sair.
Antes de nós sairmos.
With an explicit subject the infinitive takes the matching ending.
É melhor que tu ires.
É melhor tu ires. / É melhor que tu vás.
Use either the personal infinitive without que, or que with the subjunctive — not both.
Frequently asked questions
Do I have to use the personal infinitive?
You can usually avoid it with a subordinate clause and still be understood. But it is used constantly by native speakers, and not recognising it makes ordinary sentences hard to parse — so learn to read it before you worry about producing it.
How is it different from the future subjunctive?
For regular verbs the forms are identical, which is genuinely confusing. They differ for irregulars — ser gives sermos as the personal infinitive and formos as the future subjunctive — and the context tells you which is meant.
Does Spanish have anything like it?
No, and this is one of the few places where Portuguese is structurally richer. Spanish must use que plus a subjunctive where Portuguese has the choice.