Portuguese has two infinitives — the impersonal (or bare) infinitive, which never changes form, and the personal infinitive, which inflects for person and number. Choosing between them is a question learners face dozens of times a day. This page is the quick-reference answer key: short, decision-based, and designed to be consulted whenever you are unsure whether to inflect. It does not go as deep as the personal infinitive vs regular infinitive page, but it will get you to the right answer faster.
The underlying logic is simple: inflect the infinitive when you need to mark a subject that is not already clear from the main clause. If the subject is the same as the main clause, the bare infinitive is enough. If the subject is different, you often have to inflect — but not always, because some constructions block the personal infinitive entirely.
The decision tree
Work through these four questions in order. The first one that applies gives you the answer.
Question 1: Is the subject of the infinitive the same as the main clause?
If yes, use the bare infinitive. No inflection. This is the default for modals (quero, posso, devo) and for any construction where the subject carries over automatically.
Quero sair cedo.
I want to leave early. (same subject — I want, I leave)
Para chegar a horas, tenho de sair agora.
To arrive on time, I have to leave now. (same subject — bare infinitive)
Even when there is a preposition (para, sem, antes de, depois de), if the subject does not change, the bare infinitive is correct.
If no, go to Question 2.
Question 2: Is the main verb a strict volition verb? (querer, desejar, preferir)
If yes — and the subject is different — you cannot use a personal infinitive. You must use que + subjunctive.
Quero que saias agora.
I want you to leave now. (que + present subjunctive)
Desejo que tenhas um bom fim de semana.
I hope you have a good weekend.
Preferia que viesses mais tarde.
I'd rather you came later. (que + imperfect subjunctive)
The attempt quero tu saíres or prefiro vocês virem is ungrammatical. Querer, desejar, preferir block the bare personal infinitive with a subject shift.
If the main verb is not one of these strict volition verbs, go to Question 3.
Question 3: Is there a preposition introducing the infinitive?
Common prepositions: para, sem, antes de, depois de, até, ao, por, apesar de, em vez de, a fim de, além de.
If yes, and the subject is different, use the personal infinitive.
Para tu chegares a horas, tens de sair agora.
For you to arrive on time, you have to leave now.
Saí sem eles notarem.
I left without them noticing.
Antes de os miúdos acordarem, vou preparar o pequeno-almoço.
Before the kids wake up, I'll make breakfast.
Ao entrarmos na sala, toda a gente se calou.
When we entered the room, everyone went quiet.
Depois de saírem, ligámos para a polícia.
After they left, we called the police.
Apesar de estarem cansados, ficaram mais uma hora.
Although they were tired, they stayed another hour.
This is by far the most common context for the personal infinitive. Learning to reach for it automatically after a preposition with a new subject is one of the biggest wins for sounding native.
If there is no preposition, go to Question 4.
Question 4: Is there an impersonal evaluation? (é importante, é preciso, é bom, convém, etc.)
If yes, you have a choice: either the personal infinitive or que + subjunctive.
É importante tu estudares todos os dias.
It's important for you to study every day. (personal infinitive)
É importante que tu estudes todos os dias.
It's important that you study every day. (que + subjunctive)
É melhor nós irmos embora.
We'd better go. (personal infinitive)
É melhor que nós vamos embora.
It's better that we go. (que + subjunctive)
Convém chegares cedo.
It's best if you arrive early. (personal infinitive)
Convém que chegues cedo.
It's best that you arrive early. (que + subjunctive)
Both structures are grammatical. The personal infinitive is lighter and more common in conversation; que + subjunctive is slightly more formal and more common in writing. Pick based on register.
If the impersonal is making a truly generic claim (no specific subject intended), use the bare infinitive:
É importante beber muita água.
It's important to drink a lot of water. (general advice, no specific subject)
Without inflection, the claim is universal. Adding -mos or -es narrows it to a specific subject.
The decision tree visualized
| Step | Question | If yes |
|---|---|---|
| 1 | Same subject as main clause? | Bare infinitive (quero sair) |
| 2 | Main verb is querer / desejar / preferir with subject change? | Que + subjunctive (quero que saias) |
| 3 | Preposition + different subject? | Personal infinitive (para saíres, sem saberem) |
| 4 | Impersonal expression with specific subject? | Personal infinitive OR que + subjunctive (é importante estudares / é importante que estudes) |
| — | Impersonal expression with generic meaning? | Bare infinitive (é importante beber água) |
Modals and other same-subject verbs: always bare
Modals (poder, dever, querer, saber, preferir, costumar), try/manage verbs (tentar, conseguir, ousar), and aspectual verbs (começar a, continuar a, deixar de, acabar de) all operate with a same-subject infinitive. The subject of the main verb and the subject of the infinitive are the same person, always. Inflection is not needed and would produce ungrammatical results.
Não consigo adormecer com este barulho.
I can't fall asleep with this noise.
Começámos a trabalhar às oito.
We started working at eight.
Acabámos de chegar.
We've just arrived.
Writing posso eu fazermos or conseguimos adormecermos is ungrammatical — the bare infinitive is obligatory. The exception is an emphatic or contrastive use of the 1pl pronoun, which is very rare and basically literary.
The exceptional emphatic use
Some grammars note that in emphatic contexts, even modals occasionally tolerate a personal infinitive with an explicit subject pronoun. This is marginal and literary:
Podemos nós fazermos isto melhor?
Can we do this better? (emphatic, rhetorical, literary)
You will encounter this in older texts and in rhetorical speech. In modern everyday Portuguese, stick to the bare infinitive after modals.
Causative and perception verbs: bare infinitive with an object
Causative (deixar, mandar, fazer) and perception (ver, ouvir, sentir) verbs license a new subject, but they do so through an accusative object pronoun — and the infinitive stays bare.
Deixa-o entrar.
Let him in.
Vi-os sair do café.
I saw them leave the café.
Mandei-a calar-se.
I told her to be quiet.
The subject of the infinitive is already present (as the object of the causative/perception verb), so no inflection is needed. Personal-infinitive variants (vi-os saírem, mandei-os saírem) do exist and are accepted in modern European Portuguese, but the bare version is more common and simpler.
Quick reference: the five most common contexts
Here are the five most frequent situations, each with its verdict:
| Situation | Use | Example |
|---|---|---|
| Modal + infinitive (same subject) | Bare infinitive | Quero sair. |
| Preposition + infinitive (same subject) | Bare infinitive | Para chegar cedo, acordei às seis. |
| Preposition + infinitive (different subject) | Personal infinitive | Para tu chegares cedo, acorda às seis. |
| Impersonal + infinitive (specific subject) | Personal inf. OR que + subjunctive | É importante saíres já. |
| Volition verb + different subject | Que + subjunctive only | Quero que saias já. |
Memorize this table and you will have the right answer in most real sentences.
Subject pronoun and position
When you use the personal infinitive, the subject pronoun often appears directly before the inflected infinitive (para tu chegares, sem eles saberem) — or is dropped entirely when the inflection itself makes it unambiguous (para chegarmos, sem saberem).
For nós and eles/vocês, the inflection alone is sufficient because -mos and -em are unambiguous. The subject pronoun is usually dropped:
Para chegarmos a tempo, temos de sair agora.
For us to arrive on time, we have to leave now.
Saí sem saberem.
I left without them knowing.
For tu and eu/ele, the distinction matters: chegares uniquely marks tu, but chegar is ambiguous between eu and ele (both have no ending). So for eu and ele/ela, you usually keep the pronoun:
Antes de ele chegar, vamos preparar o café.
Before he arrives, we'll make coffee.
Honest acknowledgment: some cases are genuinely unclear
Not every sentence fits the decision tree cleanly. Some real Portuguese sentences sit on the boundary between two structures, and native speakers themselves may differ on preferences. A few examples:
With mandar, deixar, fazer + full NP subject
As mentioned on the infinitive after verbs page, both forms are accepted:
Mandei os miúdos arrumar o quarto.
I told the kids to tidy their room. (bare — more common)
Mandei os miúdos arrumarem o quarto.
I told the kids to tidy their room. (personal inf. — also accepted)
With pedir + indirect object + para
Both bare and personal infinitive are acceptable, though the personal infinitive is increasingly common:
Pedi-lhes para chegar a horas.
I asked them to arrive on time. (bare — traditional)
Pedi-lhes para chegarem a horas.
I asked them to arrive on time. (personal — modern standard)
After verbs of emotion
Lamento teres perdido o comboio.
I'm sorry you missed the train. (personal infinitive)
Lamento que tenhas perdido o comboio.
I'm sorry you missed the train. (que + subjunctive)
Both sound native. Choose based on rhythm and register.
When in doubt in these borderline cases, default to the personal infinitive after prepositions and to que + subjunctive after bare volition/emotion verbs. That heuristic will produce correct Portuguese the vast majority of the time.
What about gerunds?
Portuguese gerunds (falando, comendo, partindo) have a separate job — they express simultaneous action, often with a causal or conditional flavor. They are not infinitives and do not compete with them. You cannot substitute a gerund where an infinitive is expected (after prepositions, for instance, the infinitive is required in modern European Portuguese — gerunds after prepositions are a Brazilian innovation).
Saí da sala pensando no que tinha ouvido.
I left the room thinking about what I'd heard. (gerund — simultaneous action)
Saí da sala sem pensar em nada.
I left the room without thinking about anything. (infinitive after a preposition — required)
The decision tree on this page applies to infinitives (bare vs inflected), not to gerunds.
Comparison with Spanish
Spanish has only the impersonal infinitive. Every decision in the tree above collapses for a Spanish speaker: where Portuguese inflects, Spanish keeps the bare form (or switches to que + subjuntivo). This produces systematically heavier Spanish sentences, and it is why transferring Spanish habits into Portuguese produces clunky but grammatical output.
| Spanish (forced) | Portuguese (choice) |
|---|---|
| Para que lleguemos a tiempo... | Para chegarmos a tempo... (personal inf., lighter) |
| Sin que ellos lo sepan... | Sem eles saberem... (personal inf.) |
| Es importante que estudies. | É importante estudares. / É importante que estudes. (either) |
| Quiero que vengas. | Quero que venhas. (same as Spanish — no inf. option) |
Comparison with English
English uses for + pronoun + to-infinitive to approximate the Portuguese personal infinitive: "for us to arrive, for you to study, for them to know." Portuguese collapses this into a single word:
| English | Portuguese |
|---|---|
| for us to arrive | chegarmos |
| for you to study | estudares |
| for them to know | saberem |
| before the kids wake up | antes de os miúdos acordarem |
The Portuguese version is almost always more compact. Once you internalize the decision tree, you will be reaching for these compact forms automatically.
Common Mistakes
❌ Quero tu saíres já.
Ungrammatical — querer blocks the personal infinitive with a subject change. Use que + subjunctive.
✅ Quero que saias já.
I want you to leave now.
Remember the strict volition verbs: querer, desejar, preferir do not license a personal infinitive. Switch to que + subjunctive.
❌ Podemos ajudarmos-te.
Ungrammatical — modals take bare infinitives; the personal inflection -mos on the infinitive is not licensed after poder.
✅ Posso ajudar-te.
I can help you.
✅ Podemos ajudar-te.
We can help you.
Modals (poder, dever, querer, saber, preferir) take the bare infinitive. The subject of the modal and the infinitive are always the same, so there is nothing to mark.
❌ Para nós chegar cedo, acordámos às seis.
Incorrect — once nós is explicit, the infinitive must be inflected.
✅ Para nós chegarmos cedo, acordámos às seis.
For us to arrive early, we got up at six.
✅ Para chegarmos cedo, acordámos às seis.
For us to arrive early, we got up at six. (pronoun dropped)
When the subject is a nós, tu, ele, eles that differs from the main clause — or is pronounced explicitly — the infinitive must inflect.
⚠ É importante bebermos muita água.
Grammatical, but this narrows the claim to 'us' (nós). If you meant general advice for anyone, drop the inflection.
✅ É importante beber muita água.
It's important to drink a lot of water. (general advice)
✅ É importante bebermos muita água.
It's important for us to drink a lot of water. (specifically nós)
When an impersonal is making universal advice (for anyone), use the bare infinitive. Only inflect when you mean a specific subject.
❌ Antes de eles chegar, arruma a casa.
Incorrect — with eles explicit, the infinitive needs -em.
✅ Antes de eles chegarem, arruma a casa.
Before they arrive, tidy up the house.
Third-person-plural subjects require -em on the infinitive.
Key takeaways
- Same subject as main clause → bare infinitive. No exceptions for modals; rarely an exception even with prepositions.
- Strict volition verbs (querer, desejar, preferir) with subject change → que + subjunctive only. Personal infinitive is blocked.
- Preposition + different subject → personal infinitive. This is the most common and reliable use of the form.
- Impersonal expressions + specific subject → personal infinitive or que + subjunctive. Both are grammatical; pick based on register.
- Impersonal expressions with generic meaning → bare infinitive. (É importante beber água.)
- Causatives (deixar, mandar, fazer) and perception verbs (ver, ouvir, sentir) → object pronoun + bare infinitive. Personal-infinitive variants are accepted but less common.
- Drop the subject pronoun when the inflection alone makes it unambiguous (nós, eles, vocês); keep it when needed to distinguish eu from ele.
For deeper coverage, see personal infinitive vs regular infinitive and personal infinitive after prepositions.
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 vs Regular Infinitive: When to InflectB1 — The decision rules for choosing between the impersonal (bare) infinitive and the personal (inflected) infinitive — the most consulted page in this set.
- Personal Infinitive After PrepositionsB1 — The most common use of the infinitivo pessoal: after para, sem, antes de, depois de, até, and ao. Full examples of each, plus clitic placement with pronominal verbs.
- Personal Infinitive as SubjectB2 — Using the inflected infinitive as the subject of a sentence — é importante estudarmos, é bom vocês virem, lermos ajuda a memorizar — and how this competes with the que + subjunctive construction.
- Infinitive After PrepositionsA2 — Portuguese prepositions always take the infinitive — never a conjugated verb. A tour of de, a, para, em, por, sem, até, and ao, with the shift to personal infinitive when the subject matters.
- Infinitive After Other VerbsA1 — When one Portuguese verb is followed by another, the second verb is almost always an infinitive — bare or personal, with or without a linking preposition. A map of modals, aspectual verbs, causatives, and perception verbs.