In short

Portuguese has something almost no other language offers: an infinitive that carries a subject ending. Alongside the plain falar (“to speak”) sits falarmos (“for us to speak”), falarem (“for them to speak”). This infinitivo pessoal lets you keep a clear, explicit subject inside a non-finite clause, so you can say para eu saber (“so that I know”) or ao chegarmos (“on our arriving”) without building a full que-clause with a conjugated verb. Two pieces of good news: the endings are always the same, and the personal infinitive is always regular - even ser, ter and pôr follow the pattern - so there is nothing irregular to memorise.

The rule

What it is and how you build it

Start from the ordinary (impersonal) infinitive and add these personal endings:

• eu: - (nothing)
• tu: -es
• ele / ela / você: - (nothing)
• nós: -mos
• vós: -des
• eles / elas / vocês: -em

Because the eu and the ele slots add nothing, they look identical to the plain infinitive; the ending is only visible for tu, nós, vós and eles. Crucially, the endings attach to the whole infinitive, irregular verbs included:

• fazer -> fazermos, fazerem (not a rebuilt stem).
• ser -> sermos, serem; ter -> termos, terem; pôr -> pormos, porem.

So once you can say the infinitive, you can inflect it. There are no exceptions to learn.

When to use it: three triggers

The personal infinitive appears where an infinitive clause has a subject of its own, especially in these contexts.

1. After a preposition or prepositional phrase. This is the commonest case. para, por, sem, até, ao, antes de, depois de, apesar de, em vez de govern a personal infinitive when the action has its own subject:

• Comprei um bolo para comermos ao lanche. (“…for us to eat.”)
• Saíram sem eles se despedirem. (“…without them saying goodbye.”)
• Telefona-me depois de acabares o trabalho. (“…after you finish…”)

The phrase ao + personal infinitive is a compact way to say “on / upon …-ing”: Ao chegarem a casa, começou a chover (“On arriving home, it started to rain”).

2. After an impersonal expression. é importante, é melhor, é preciso, é possível, convém, basta take a personal infinitive to pin down whose action it is:

• É melhor esperarmos aqui. (“It’s better for us to wait here.”)
• É importante os alunos lerem o texto. (“It’s important that the students read the text.”)

Compare the bare, general É importante ler (“It’s important to read”, anyone) with the inflected É importante lermos (“…that we read”).

3. As or with an explicit subject. When the infinitive clause is itself the subject or is felt as a small clause: Foi difícil eles aceitarem a proposta (“It was hard for them to accept the offer”).

When NOT to inflect

Do not inflect an infinitive that simply completes a conjugated verb of the same subject - the modal and phase verbs poder, querer, dever, ir, começar a, ter de:

• Queremos sair, never queremos sairmos.
• Podem entrar; Vou fazer o jantar.

The personal infinitive lives in a separate clause (after a preposition or an impersonal expression), not as the direct complement of an auxiliary. If the two verbs share one subject and one clause, keep the plain infinitive.

Personal infinitive or subjunctive?

A prepositional clause with a different subject can often be phrased either with que + subjunctive or with a personal infinitive, and European Portuguese usually prefers the lighter infinitive:

• Falei devagar para eles perceberem. = …para que eles percebessem.
• Avisa-me antes de saíres. (same subject felt, still inflected for clarity)

Rule of thumb: preposition + own subject -> personal infinitive; a full que-clause is the heavier, more formal alternative.

Forms & patterns

The endings on the three conjugations and on irregular verbs (all regular in shape):

Common triggers:

Examples

Common mistakes

• Queremos sairmos cedo -> Queremos sair cedo - an infinitive completing a same-subject modal (querer, poder, dever) stays plain; never inflect it.
• para que eu saber -> para eu saber (or para que eu saiba) - after a preposition use the personal infinitive; que would force a conjugated subjunctive.
• É melhor tu ir mais cedo -> É melhor tu ires mais cedo - when the subject is expressed, inflect: ires, not the bare ir.
• depois de nós comer -> depois de nós comermos - the nós ending is -mos on the infinitive.
• sem eles vem -> sem eles verem - verem is the personal infinitive of ver; vem is the present of vir.
• para fazermos when eu is the subject -> para fazer / para eu fazer - match the ending to the real subject; -mos is only for nós.
• Building a future-looking form: falaremos for “for us to speak” -> falarmos - falaremos is the future indicative, a different tense.

Tips

• The tell-tale trigger is a preposition followed by a subject - para eu, sem eles, antes de tu, ao nós. See that shape and inflect.
• Only tu (-es), nós (-mos), vós (-des) and eles (-em) show a visible ending; eu and ele look exactly like the plain infinitive, which is why the form is easy to miss.
• Relax about irregular verbs: the personal infinitive is built on the infinitive, so ser, ter, fazer, pôr, ir are all perfectly regular here - the one corner of the verb system with no surprises.
• Think of ao + personal infinitive as a ready-made “on …-ing” clause: ao chegarem, ao terminarmos, ao ver isso.
• Reach for it whenever a que + subjunctive clause feels heavy: para eles perceberem is the everyday European Portuguese way to say para que eles percebam.
• In Brazil: the inflected infinitive is equally standard and used the same way; the difference you may notice is stylistic, with the personal infinitive often preferred over a que-clause in both varieties of careful writing.