The personal infinitive (infinitivo pessoal) is one of the few grammatical features Portuguese has that almost no other language does, and English has nothing like it at all. Because of that, the errors English speakers make with it are not the errors you might expect. The classic mistakes are not "wrong endings" — they are not using the personal infinitive in the first place, and reaching for a clumsier subjunctive construction instead. This page collects the real transfer errors, explains the logic behind each correction, and trains you to actively recognize when the construction is calling for the personal infinitive.
A quick reminder of the forms
The personal infinitive takes the plain infinitive and adds person endings to it. There is nothing to "stem-change" — you build it straight off the infinitive itself.
| Person | falar | comer | partir |
|---|---|---|---|
| eu | falar | comer | partir |
| você / ele / ela | falar | comer | partir |
| nós | falarmos | comermos | partirmos |
| vocês / eles / elas | falarem | comerem | partirem |
The endings that actually appear are -mos (nós) and -em (vocês/eles). The singular forms look identical to the plain infinitive — which is exactly why English speakers forget the inflected forms exist.
Error 1: Forgetting to inflect (the big one)
The single most common error is leaving the infinitive uninflected when its subject is plural. English has no inflected infinitive, so your instinct produces a bare infinitive every time.
❌ Para nós sair cedo, temos que acordar às seis.
Incorrect — the infinitive must agree with nós: sairmos, not sair.
✅ Para nós sairmos cedo, temos que acordar às seis.
For us to leave early, we have to wake up at six.
❌ É hora de vocês ir embora.
Incorrect — the subject is vocês, so the infinitive must be irem.
✅ É hora de vocês irem embora.
It's time for you all to leave.
The reason it matters: in a sentence like É hora de irem, the -em ending is what tells the listener the subject is "you all / they" rather than "I / he / she." Drop the ending and you have not just made a grammatical slip — you have removed information the listener needs.
É difícil eles entenderem essa explicação.
It's hard for them to understand that explanation.
Error 2: Inflecting when the subject is shared with the main clause
The mirror-image mistake: over-applying the rule. If the infinitive's subject is the same as the main verb's subject, you normally use a plain (uninflected) infinitive. Inflecting here is not strictly ungrammatical in every context, but it sounds heavy and is usually wrong in everyday speech.
❌ Nós queremos sairmos cedo.
Incorrect — the subject of querer and of sair is the same (nós), so use the plain infinitive.
✅ Nós queremos sair cedo.
We want to leave early.
❌ Eles precisam estudarem mais.
Incorrect — precisar and estudar share the same subject; no inflection.
✅ Eles precisam estudar mais.
They need to study more.
The logic: with verbs like querer, precisar, poder, conseguir, dever (modal-type verbs that take a direct infinitive), the infinitive belongs to the same subject and forms a single verb chain. There is no second subject to mark, so there is nothing for the inflection to do.
Error 3: Reaching for the subjunctive when the personal infinitive is cleaner
This is the subtlest and most revealing error, and it usually comes from learners who studied Spanish or who learned the subjunctive first. After impersonal expressions like é melhor, é bom, é importante, é difícil, both a subjunctive clause and a personal infinitive are grammatical — but Brazilian Portuguese strongly prefers the personal infinitive when the subject is explicit, because it is shorter and lighter.
É melhor que nós saiamos agora.
It's better that we leave now. (Grammatical, but heavy and a little formal.)
É melhor nós sairmos agora.
It's better for us to leave now. (Natural, everyday Brazilian Portuguese.)
Notice that the second version drops the conjunction que entirely and replaces the subjunctive saiamos with the personal infinitive sairmos. Both communicate the same thing; the infinitive version is what a native speaker says at the dinner table.
Foi bom vocês virem.
It was good that you all came.
É importante eles assinarem o documento hoje.
It's important for them to sign the document today.
The error, then, is not producing something wrong — it is producing something correct but stiff (é melhor que saiamos) when the idiomatic choice was right there. Train yourself: after an impersonal expression with a named subject, default to the personal infinitive.
Error 4: Confusing the personal infinitive with the future subjunctive
For regular verbs these two forms can look alike, which masks the problem. But for irregular verbs they diverge sharply, and that is where the confusion surfaces. Both are inflected, both can take -mos and -em, but they appear in different syntactic slots.
The future subjunctive shows up after time/condition conjunctions like quando, se, assim que, enquanto. The personal infinitive shows up after prepositions like para, de, por, até, and after impersonal expressions.
| Verb | Future subjunctive (após quando/se) | Personal infinitive (após para/de) |
|---|---|---|
| ser | quando nós formos | para nós sermos |
| ter | quando eles tiverem | para eles terem |
| fazer | quando vocês fizerem | para vocês fazerem |
| vir | quando nós viermos | para nós virmos |
Quando nós formos ao Brasil, vamos visitar Salvador.
When we go to Brazil, we're going to visit Salvador. (future subjunctive)
Para nós sermos sinceros, a viagem foi cansativa.
For us to be honest, the trip was tiring. (personal infinitive)
The trap: a learner who knows quando formos may try to say para nós formos, which is wrong — after para you need the infinitive sermos. The irregular future subjunctive of ser is formos, but the personal infinitive of ser is built straight off the infinitive: ser + mos = sermos.
Why the real problem is under-use, not error
Step back and the pattern is clear: errors 1, 3, and 4 are all forms of the same thing — an English speaker's grammar does not generate the personal infinitive on its own, so the brain substitutes whatever it does have: a bare infinitive (error 1), a subjunctive clause (error 3), or the wrong inflected form (error 4). You will rarely over-produce the personal infinitive; you will chronically under-produce it.
This means your training goal is the opposite of most grammar points. Instead of suppressing a wrong instinct, you have to install a new one. Build the habit of scanning for the triggers — a preposition followed by a subject, or an impersonal expression with a named subject — and actively reaching for the inflected infinitive there.
Trouxe um casaco para vocês não passarem frio.
I brought a jacket so you all wouldn't get cold.
Depois de os convidados saírem, limpamos tudo.
After the guests left, we cleaned everything up.
Common Mistakes
❌ Comprei pão para nós comer no café da manhã.
Incorrect — after para with the subject nós, the infinitive must inflect.
✅ Comprei pão para nós comermos no café da manhã.
I bought bread for us to eat at breakfast.
❌ Antes de eles chegar, arrume a casa.
Incorrect — the subject eles requires the inflected infinitive chegarem.
✅ Antes de eles chegarem, arrume a casa.
Before they arrive, tidy the house.
❌ Eu quero comprarmos uma casa.
Incorrect — querer and comprar share no separate subject here; the standard reading drops the inflection.
✅ Eu quero que nós compremos uma casa. / Queremos comprar uma casa.
I want us to buy a house. / We want to buy a house.
❌ É melhor que vocês ir agora.
Incorrect — mixes a que-clause with a bare infinitive; pick one structure.
✅ É melhor vocês irem agora.
It's better for you all to go now.
❌ Para nós fazermos isso, precisamos quando tivermos tempo.
Incorrect — para takes the personal infinitive (fazermos ✓) but the second clause needs a clean structure, not a stray future subjunctive.
✅ Para fazermos isso, precisamos de tempo. Faremos quando tivermos tempo.
To do that, we need time. We'll do it when we have time.
Key Takeaways
- The infinitive inflects (-mos, -em) when it has a subject distinct from, or explicitly named alongside, the main verb.
- Keep the plain infinitive when the subject is shared with a modal-type verb (querer, precisar, poder).
- After impersonal expressions with a named subject, prefer the personal infinitive over a full subjunctive clause — it is the natural Brazilian choice.
- Do not confuse the personal infinitive (after prepositions) with the future subjunctive (after quando, se); for irregular verbs they look completely different.
- Your real task is to use the personal infinitive more, not to avoid misusing it.
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Start learning Portuguese→Related Topics
- 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.
- The Personal Infinitive: OverviewB1 — Portuguese's signature feature — an infinitive that carries person and number endings, letting infinitive clauses take their own subject.
- Personal Infinitive Replacing Subjunctive ClausesB2 — How Brazilian Portuguese uses the personal infinitive as a more concise, modern-sounding alternative to que + subjunctive clauses.
- 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.
- Personal Infinitive ErrorsB1 — How English speakers under-use, over-use, and confuse the Portuguese personal infinitive — with ❌/✅ fixes and the logic behind the inflected endings.
- Futuro do Subjuntivo: FormationA2 — How to build the future subjunctive in Brazilian Portuguese — derived from the third-person plural preterite, and why it looks deceptively like the infinitive.