Personal Infinitive

The Personal Infinitive is one of the most distinctive features of Portuguese. It functions as a bridge between a noun-like infinitive and a fully conjugated verb.

1. Formation
It is highly regular. You take the impersonal infinitive (the dictionary form) and add these endings:

• eu: (no ending) - falar
• tu: -es - falares
• ele/ela/você: (no ending) - falar
• nós: -mos - falarmos
• vós: -des - falardes
• eles/elas/vocês: -em - falarem

Even irregular verbs like ser (sermos) and ir (irmos) follow this pattern. Because the 1st and 3rd person singular take no endings, they are 100% identical to the impersonal infinitive and rely on context (like an explicit subject pronoun) to be distinguished. Conversely, for tu, nós, and eles/elas/vocês, the subject pronoun is usually dropped because the ending makes the subject obvious. Note that the verb pôr loses its circumflex accent only in the forms that take an additional ending (pores, pormos, pordes, porem), but retains it in the 1st and 3rd person singular (para eu pôr, para ele pôr) to distinguish it from the preposition por.

2. The Identity Crisis (Personal Infinitive vs. Future Subjunctive)
For all regular verbs, the Personal Infinitive and the Future Subjunctive are identical in form (e.g., falares can be either). This is a major source of confusion for learners! The key difference is the trigger: the Personal Infinitive is triggered by prepositions (like para, por, sem) and impersonal expressions, while the Future Subjunctive is triggered by conjunctions (like se or quando) and relative pronouns (e.g., quem, o que, onde). They only differ in verbs with an irregular preterite stem (e.g., sermos vs. formos). This happens because the Personal Infinitive is always built from the infinitive stem, whereas the Future Subjunctive is built from the 3rd-person plural preterite stem (by taking the 3rd-person plural of the pretérito perfeito do indicativo and dropping the '-am' ending).

3. When to Use It
The most common triggers are:

• After Prepositions: Used with para, sem, ao, and depois de.
• Subject Clarity and Emphasis: The core rule is 'Same Subject vs. Different Subject'. If the subject of the infinitive is the same as the main verb, use the impersonal infinitive (e.g., Eu comprei o bolo para [eu] comer). If the subject is different, use the personal infinitive (e.g., Eu comprei o bolo para comermos). It can also be used with the same subject to emphasize the agent.
• Impersonal Expressions: After phrases like 'É preciso' (It is necessary) or 'É bom' (It is good) to specify who the action applies to, but only when there is no 'que' (e.g., É importante nós estudarmos). If the expression is followed by 'que', it triggers the Subjunctive instead (e.g., É importante que nós estudemos).
• As a Subject: It can act as the subject or topic of a sentence (e.g., Fumares faz mal or Lermos ajuda a memorizar).

4. When NOT to Use It (Compound Verbs)
A critical restriction is that the Personal Infinitive is never used as the main verb in a compound verb phrase (locução verbal). In these cases, only the auxiliary verb is conjugated, and the main verb must remain in the impersonal infinitive. For example, you must say Eles devem estudar, never Eles devem estudarem.

5. The Preposition Contraction Rule
A crucial rule in formal grammar is that prepositions (like de or em) must not contract with the subject pronoun of a personal infinitive. For example, you must write apesar de eles saberem, not apesar deles saberem. This is a common trap for learners!

6. Regional Differences
In European Portuguese, this form is essential for natural speech. In Brazilian Portuguese, while common in writing and formal speech, speakers often replace it with a que + subjunctive construction. In casual Brazilian conversation, speakers frequently drop the plural endings entirely, using the impersonal infinitive with an explicit subject (e.g., para eles fazer) or relying on a gente (e.g., para a gente fazer).