The personal infinitive is one of the most distinctive features of Portuguese, and it is also one of the most frequently mishandled by learners. The mistakes tend to come from two opposite directions: over-inflating (using a personal infinitive when a plain infinitive is called for) and under-inflating (failing to mark the person when it is required). A third major trap is confusing the personal infinitive with the future subjunctive, since regular verbs produce identical forms in the two paradigms.
This page gathers the ten most common errors and shows exactly how to fix them. If you internalize these patterns, you will eliminate roughly 90% of the personal-infinitive mistakes that English-speaking learners make.
Over-inflation: inflecting when you shouldn't
The most common mistake is inflecting the infinitive when the subject of the main verb and the embedded verb are the same. Same-subject constructions take the impersonal infinitive — no person marking at all. The personal infinitive is only for different-subject or prepositional-with-subject-switch contexts.
Mistake 1: Inflating with querer + same subject
❌ Eu quero sabermos a verdade.
Incorrect — 'sabermos' is 1pl, but the subject of 'quero' is 1sg. Subject mismatch is impossible here.
✅ Eu quero saber a verdade.
I want to know the truth. (same subject — impersonal infinitive)
✅ Eu quero que nós saibamos a verdade.
I want us to know the truth. (different subject: eu + nós — subjunctive required)
After querer, if the subject of querer and the embedded verb are the same, use the impersonal infinitive. If they are different, you must use que + conjuntivo — the personal infinitive is not an option because querer is a volition verb.
This is the trap that catches most English speakers first: they hear "inflected infinitive" and decide to inflect every infinitive they see. The personal infinitive is specifically for marking a subject that is not already supplied by the main clause.
Mistake 2: Inflating in same-subject prepositional phrases
❌ Antes de saírmos, eu fechei a janela.
Incorrect if the subject of saírmos and fechei is the same.
✅ Antes de sair, eu fechei a janela.
Before I left, I closed the window. (same subject — impersonal infinitive)
When the subject of the prepositional clause is the same as the subject of the main clause, no inflection is needed. Saírmos (1pl) contradicts the 1sg subject of fechei — the inflection would imply we left, not I left.
Mistake 3: Inflating after é + adjective when the statement is generic
❌ É importante estudarmos muito para ter sucesso.
Incorrect if generic — 'estudarmos' implies a specific nós subject.
✅ É importante estudar muito para ter sucesso.
It's important to study a lot to succeed. (generic life advice)
✅ É importante estudarmos muito para o exame de amanhã.
It's important for us to study a lot for tomorrow's exam. (specific us)
When an impersonal expression is making a generic statement ("anyone who wants to succeed should study"), use the plain infinitive. Inflating it implies a specific group and changes the meaning.
Under-inflation: not inflecting when you should
The opposite mistake is failing to mark the person when it is required. This often comes from treating the Portuguese infinitive like the English "to-infinitive," which never changes form.
Mistake 4: Missing inflection with different subject
❌ Para nós fazer os trabalhos, precisamos de silêncio.
Incorrect — personal infinitive with nós subject must be 'fazermos,' not 'fazer.'
✅ Para nós fazermos os trabalhos, precisamos de silêncio.
For us to do the work, we need quiet.
When the preposition introduces a clause with a subject different from (or additional to) the main clause's subject, Portuguese requires the personal infinitive. Para + nós + fazer is ungrammatical in modern EP — it has to be para (nós) fazermos.
Mistake 5: Missing inflection with impersonal expressions
❌ É preciso tu falar com ele antes da reunião.
Incorrect — with explicit subject 'tu,' the infinitive must be inflected: 'falares.'
✅ É preciso tu falares com ele antes da reunião.
You need to talk to him before the meeting.
✅ É preciso falar com ele antes da reunião.
It's necessary to talk to him before the meeting. (generic)
Once you name a subject (tu), the infinitive must match it. É preciso tu falar breaks agreement — EP requires falares to match tu.
Mistake 6: Missing inflection in 3pl contexts
❌ Sem eles saber o que se passa, não podemos avançar.
Incorrect — 'saber' must match the 3pl subject: 'saberem.'
✅ Sem eles saberem o que se passa, não podemos avançar.
Without them knowing what's going on, we can't move forward.
This is one of the most frequent errors. Learners from Spanish or English produce sem eles saber because their native language has only one infinitive form. EP forces saberem to match the 3pl subject.
Future subjunctive vs personal infinitive confusion
Because regular verbs have identical forms in the personal infinitive and the future subjunctive, learners sometimes confuse which one is required in a given slot. The confusion is harmless for regular verbs (the form is the same), but it becomes visible with irregular verbs.
Mistake 7: Mixing up the two with irregular verbs
❌ Quando eu vir à festa, trago o bolo.
Incorrect — after 'quando' with future reference, you need the future subjunctive 'vier,' not the personal infinitive 'vir.'
✅ Quando eu vier à festa, trago o bolo.
When I come to the party, I'll bring the cake. (vier = future subj of vir)
✅ Para eu vir à festa, preciso de pedir boleia.
For me to come to the party, I need to ask for a ride. (vir = 1sg personal inf of vir, triggered by the preposition 'para')
The verb vir is instructive. Its personal infinitive is vir, vires, vir, virmos, virem. Its future subjunctive is vier, vieres, vier, viermos, vierem. A learner who writes quando eu vir a festa for "when I come to the party" has mixed up the two paradigms — after quando, you need the future subjunctive vier, not the personal infinitive vir.
Mistake 8: Using personal infinitive after se/quando/enquanto
❌ Se tu fores cedo, podemos jantar juntos. (meaning 'if you arrive early')
Mismatch — 'fores' is future subj of 'ser' or 'ir,' not of 'chegar.' For 'if you arrive,' you want 'se chegares.'
✅ Se tu chegares cedo, podemos jantar juntos.
If you arrive early, we can have dinner together. (future subjunctive after se)
✅ Para chegares cedo, tens de sair já.
In order for you to arrive early, you have to leave now. (personal infinitive after para)
With regular verbs like chegar, the form chegares is identical for both paradigms — so no visible error arises. But with irregular verbs, picking the wrong paradigm produces a wrong form (se tu vires vs se tu vieres for vir). The trigger (se/quando/enquanto vs para/sem/antes de) tells you which paradigm is active.
Wrong agreement: form/subject mismatch
Mistake 9: 3pl subject with non-3pl ending
❌ Para eles fazer os trabalhos de casa, precisam de concentração.
Incorrect — 3pl subject requires 3pl ending: 'fazerem.'
✅ Para eles fazerem os trabalhos de casa, precisam de concentração.
For them to do their homework, they need concentration.
The personal infinitive endings are: tu → -es, nós → -mos, eles → -em. A 3pl subject (eles, elas, vocês) requires -em. The ending -er (bare infinitive of fazer) does not agree with eles.
Mistake 10: 2sg and 3sg confusion
❌ É importante tu falar com ele.
Incorrect — 'tu' requires the 2sg ending '-es': 'falares.'
✅ É importante tu falares com ele.
It's important that you talk to him.
Learners often under-inflect the 2sg because the ending -es is easy to forget. Tu requires falares, comeres, partires — never falar, comer, partir once the pronoun is present.
The pôr problem: preserving the circumflex
The verb pôr (to put) and its compounds (compor, dispor, propor, supor, impor, depor, repor) keep the circumflex accent in several but not all personal infinitive forms. Here is the complete paradigm:
| Person | Personal infinitive of pôr |
|---|---|
| eu | pôr |
| tu | pores |
| ele / você | pôr |
| nós | pormos |
| eles / vocês | porem |
The 1sg and 3sg forms keep the circumflex (pôr) because the form is still one syllable with a stressed ô. The inflected forms (pores, pormos, porem) drop the circumflex because the stress shifts to the ending and the o becomes a short vowel.
Mistake: Omitting the circumflex on the bare pôr
❌ É melhor por a mesa antes de eles chegarem.
Incorrect spelling — pôr requires the circumflex when uninflected.
✅ É melhor pôr a mesa antes de eles chegarem.
It's better to set the table before they arrive.
The bare infinitive pôr always carries the circumflex. Without it, you get por — the preposition "by" or "for." É melhor por a mesa would mean "it's better by the table," which is nonsense in context.
Mistake: Adding the circumflex to inflected forms
❌ É importante pôrmos a casa em ordem.
Incorrect spelling — inflected personal infinitive drops the circumflex.
✅ É importante pormos a casa em ordem.
It's important for us to put the house in order.
When the personal infinitive form has a multi-syllable ending (-ores, -ormos, -orem), the stress shifts off the o and the circumflex disappears. Pormos is the correct 1pl form; pôrmos is a common misspelling.
Preposition triggers: para vs para que
A final mistake that comes up often is mixing up the preposition para (which takes the infinitive) with the conjunction para que (which takes the subjunctive). The meanings are effectively identical, but the triggers require different verb forms.
Mistake: Using personal infinitive after para que
❌ Para que tu saberes a verdade, tenho de te contar tudo.
Incorrect — para que triggers subjunctive, not infinitive.
✅ Para que tu saibas a verdade, tenho de te contar tudo.
So that you know the truth, I have to tell you everything. (subjunctive)
✅ Para tu saberes a verdade, tenho de te contar tudo.
For you to know the truth, I have to tell you everything. (personal infinitive)
Para + personal infinitive and para que + subjunctive are semantically equivalent and both grammatical. The mistake is trying to combine them — para que + personal infinitive is not a possible construction.
Mistake: Using subjunctive after para (without que)
❌ Para tu saibas a verdade, tenho de te contar tudo.
Incorrect — 'para' alone wants the infinitive, not the subjunctive.
✅ Para saberes a verdade, tenho de te contar tudo.
For you to know the truth, I have to tell you everything.
The preposition para takes an infinitive (often personal). The subjunctive only appears after the conjunction para que.
Other less frequent but important errors
Using personal infinitive after volition verbs
❌ Espero tu chegares a tempo.
Incorrect — esperar with subject change requires que + subjunctive.
✅ Espero que chegues a tempo.
I hope you arrive on time.
Volition verbs (querer, esperar, desejar, pedir, preferir) with a subject change require que + conjuntivo. The personal infinitive is blocked — this is not a stylistic choice.
Missing preposition with verbs that require it
❌ Tenho medo ele cair.
Incorrect — ter medo takes 'de' when followed by a clause or infinitive.
✅ Tenho medo de ele cair.
I'm afraid of him falling. (plain infinitive preceded by de, with explicit subject 'ele')
✅ Tenho medo que ele caia.
I'm afraid he'll fall. (subjunctive alternative)
Ter medo takes the preposition de before an infinitive (or before any noun phrase). Dropping it is ungrammatical.
Confusing persons: 1pl form with other subjects
❌ É importante fazermos o teste quando tu estiveres pronto.
Incorrect — fazermos is 1pl, but the sentence is about tu being ready.
✅ É importante fazeres o teste quando estiveres pronto.
It's important that you do the test when you're ready. (both verbs match 'tu')
Agreement errors often appear when learners hurry: they inflect one verb to match nós and the other to match tu, producing a sentence that makes no sense. Check agreement across the whole sentence.
A systematic checklist
Before finalizing any sentence with a personal infinitive, run through this checklist:
- Is the subject of the embedded verb the same as the subject of the main verb? If yes, use the plain infinitive. If no, consider the personal infinitive.
- Is the main verb a volition/emotion/doubt verb (querer, esperar, duvidar)? If yes, with a subject change, use que + conjuntivo — the personal infinitive is not available.
- Does the ending match the subject? Check: tu → -es, nós → -mos, eles → -em.
- Is there a preposition (para, sem, antes de, depois de, até)? If yes, use the personal infinitive, not que + subjunctive.
- Is there a conjunction (para que, antes que, sem que, embora, caso)? If yes, use the subjunctive, not the personal infinitive.
- Does the embedded clause refer to a future event after quando/se/enquanto? If yes, use the future subjunctive (which looks the same as the personal infinitive for regular verbs, different for irregular).
- If the verb is pôr, is the circumflex right? Keep it on pôr (1sg/3sg); drop it on pores, pormos, porem.
Common Mistakes Summary
❌ Eu quero sabermos a verdade.
Incorrect — same subject, should be impersonal infinitive.
✅ Eu quero saber a verdade.
I want to know the truth.
❌ Para nós fazer, precisamos de tempo.
Incorrect — nós subject requires inflected form.
✅ Para nós fazermos, precisamos de tempo.
For us to do it, we need time.
❌ É importante tu falar com ele.
Incorrect — explicit subject tu requires -es ending.
✅ É importante tu falares com ele.
It's important for you to talk to him.
❌ Sem eles saber, não podemos decidir.
Incorrect — 3pl requires -em ending.
✅ Sem eles saberem, não podemos decidir.
Without them knowing, we can't decide.
❌ Para que tu saberes.
Incorrect — 'para que' triggers subjunctive, not personal infinitive.
✅ Para que tu saibas.
So that you know. (subjunctive)
✅ Para tu saberes.
For you to know. (personal infinitive)
❌ É melhor por a mesa.
Incorrect — the infinitive pôr always carries the circumflex.
✅ É melhor pôr a mesa.
It's better to set the table.
❌ Quero que eles irem.
Incorrect — mixing que with personal infinitive.
✅ Quero que eles vão.
I want them to go. (subjunctive)
❌ Espero tu chegares cedo.
Incorrect — esperar with subject change wants que + subjunctive.
✅ Espero que chegues cedo.
I hope you arrive early.
❌ Tenho medo ele cair.
Incorrect — missing preposition 'de.'
✅ Tenho medo de ele cair.
I'm afraid he might fall.
❌ Quando eu vir à festa.
Incorrect if meaning 'when I come' — 'vir' is personal inf, future subj is 'vier.'
✅ Quando eu vier à festa.
When I come to the party.
Key takeaways
- Do not inflate when the subject of the embedded verb matches the main verb's subject — use the plain infinitive.
- Do inflate when the subject is different and a preposition or impersonal expression allows it.
- Do not inflate after volition/emotion/doubt verbs (querer, esperar, duvidar) with subject change — use que + conjuntivo instead.
- Check agreement: tu → -es, nós → -mos, eles → -em. These are not optional.
- Watch for pôr: keeps the circumflex in 1sg/3sg (pôr); drops it in inflected forms (pores, pormos, porem).
- Distinguish triggers: para → personal infinitive; para que → subjunctive. Never combine.
- Regular verbs = same form for personal infinitive and future subjunctive. Irregular verbs = different forms. Know which paradigm each trigger calls for.
- Most learner mistakes cluster around five verbs: querer, esperar, ter medo (de), pôr, vir. Drill these first.
For the full paradigm and formation rules, see Forming the Personal Infinitive. For the decision between infinitive and subjunctive, see Personal Infinitive vs Subjunctive. For advanced uses including clitic placement, see Personal Infinitive in Complex Sentences.
Related Topics
- Personal Infinitive: OverviewB1 — The infinitivo pessoal — an infinitive that conjugates for person and number — is Portuguese's signature grammatical feature, and one of the things that makes the language feel unlike the rest of Romance.
- Personal Infinitive: FormationB1 — How to build the infinitivo pessoal: take the infinitive and add the personal endings -es, -mos, -em. No stem changes, no irregularities — the only exception is pôr, which keeps its circumflex.
- Personal Infinitive vs SubjunctiveB2 — Choosing between the inflected infinitive and que + conjuntivo — where the two compete, where one is forced, and what native European Portuguese speakers actually say.
- Personal Infinitive with Impersonal ExpressionsB2 — É importante nós estudarmos vs é importante que nós estudemos — a full treatment of the personal infinitive after é + adjective constructions and related impersonal triggers.
- Personal Infinitive in Complex SentencesC1 — Advanced uses of the personal infinitive: absolute clauses, causative and permissive constructions, topicalization, clitic placement, and disambiguation from the future subjunctive.
- Future Subjunctive OverviewB1 — The futuro do conjuntivo — a living, everyday tense in European Portuguese that marks uncertain future events after temporal, conditional, and relative triggers. Almost extinct in Spanish; thriving in Portuguese.