Personal Infinitive After Prepositions

In English, we say "for us to go." The word "go" doesn't change. In Portuguese, we change the verb to match "us." This happens specifically after prepositions. Prepositions are words like para, sem, or ao. Usually, infinitives are impersonal. They don't point to a specific person. But the personal infinitive is different. It carries a little tag at the end. This tag tells us who the subject is. It is like a name tag for your verb. You use it when the subject is clear. Or when the subject changes between two parts of a sentence. It’s like a grammar traffic light. It directs the flow of who is doing what. Yes, even native speakers mess this up sometimes! So don't worry if it feels weird at first.

1. 1Forming this is actually quite simple. You start with the regular infinitive. Then, you add specific endings. It is much easier than the subjunctive! Follow these steps:
2. 2Take the base infinitive (e.g., falar, comer, ir).
3. 3For eu, add nothing. It stays the same.
4. 4For tu, add -es to the end.
5. 5For ele/ela/você, add nothing. It stays the same.
6. 6For nós, add -mos to the end.
7. 7For vós, add -des (rarely used, but good to know!).
8. 8For eles/elas/vocês, add -em to the end.
9. 9That is it! No irregular stems to memorize here. Even the most rebellious verbs follow this rule. Ir becomes irmos. Ser becomes serem. It is refreshingly consistent for Portuguese grammar.

You use the personal infinitive after prepositions. This is the golden rule. The most common triggers are para, sem, antes de, and depois de. Use it when the subject of the infinitive is different from the main subject. For example: "I bought bread for us to eat." Here, "I" bought it, but "we" eat it. You also use it to avoid ambiguity. If you just say para comer, who is eating? The personal infinitive para comermos clears that up instantly. Use it in formal writing to sound precise. Use it in casual speech to move faster. It’s great for job interviews: "Antes de vocês decidirem..." (Before you decide...). It works perfectly for directions: "Ao chegarem à esquina..." (Upon arriving at the corner...).

Don't use it if the subject is the same and there's no confusion. If I say "I want to sleep," just use the regular infinitive. Quero dormir is perfect. Saying Quero eu dormir sounds like you've had too much wine. Also, avoid it after modal verbs. Verbs like poder, dever, or querer take the impersonal infinitive. You wouldn't say Podemos falarmos. Just say Podemos falar. It is also unnecessary if the subject is general or universal. If you are making a general statement like "To live is to suffer," keep it simple. No need to conjugate for everyone in the world! Think of it like salt. Use it to bring out the flavor, but don't overdo it.

The biggest mistake is the eles form. People often forget the -em ending. They say para eles falar instead of para eles falarem. This sounds very "Tarzan-like" to a native ear. Another trap is the eu and ele forms. Since they have no ending, they look like the impersonal infinitive. This is fine, but sometimes you need to add the pronoun for clarity. Don't confuse this with the Future Subjunctive! They look identical for regular verbs. But the Future Subjunctive is for "if/when" scenarios. The Personal Infinitive is for prepositions. Finally, watch out for para mim vs para eu. Use para eu [verb] when you are the subject. Para mim is only for when the sentence ends or the action is done to you.

Let's compare this to the impersonal infinitive. The impersonal version is for general ideas. "Eating is good" is Comer é bom. The personal version is for specific people. "For us to eat is good" is Para comermos é bom. Now, compare it to the que + Subjunctive pattern. You could say Espero que eles venham. Or you could use a preposition: Estou aqui para eles virem. The personal infinitive is often shorter. It feels more direct and modern. It’s the difference between taking the highway and a winding backroad. Both get you there, but one is much more efficient.