Register is the choice of language we make according to the context, the interlocutor, and the purpose. In Portuguese, we speak of formal register when we follow norms and maintain social distance, and informal register when we use closer and more spontaneous language. Recognizing the register is the first step to choosing words and structures that are appropriate.

Formal register is used in situations with greater social distance, in public or professional contexts, and when we want to convey respect or impersonality. It is also common in official written texts, academic works, and announcements. The focus is on clarity, grammatical correctness, and structured courtesy.

Informal register is used among people who are close, in everyday conversations and in private contexts. It appears frequently in speech among friends, family, and in quick messages. The focus is on naturalness, efficiency, and interpersonal connection.

Formal register tends to avoid slang and diminutives and prefers complete constructions and respectful forms of address. Informal register accepts shorter sentences, interruptions, and affectionate vocatives. The choice of pronouns and forms of addressing the interlocutor signals the degree of formality.

'You' is pronominally informal in much of contemporary Brazil, although it can sound neutral in some urban contexts. 'Mr.' and 'Ms.' are formal forms of address, associated with respect and distance. The choice between these forms changes the perception of respect and proximity in the conversation.

Formal register prefers more neutral and precise words, while informal uses reductions, slang, and colloquial expressions. Some words change tone depending on the context, even when they are not slang. The choice of vocabulary changes the impression left by the speaker or writer.

Formal register favors complete sentences, direct order, and explicit cohesion with connectors. Questions and requests appear with modals or verbs in the conditional, creating politeness. Justifications and conclusions are usually introduced by expressions such as 'therefore' and 'in this way'.

Informal register accepts ellipses, short phrases, and fragmented constructions, especially in speech and digital writing. Requests may appear without modals, sounding more direct. Repetition and interjections are common to convey engagement or emphasis.

Slang is a strong mark of informality and changes quickly depending on region, age, and social group. Idiomatic expressions can also sound more informal, depending on the context. In formal situations, it is recommended to avoid slang and choose neutral equivalents.

Some choices sound more formal or informal depending on the region of Brazil, in addition to vocabulary differences. Still, the central difference between formal and informal remains valid: suitability to the context and the interlocutor. Being understood across the country generally involves preferring neutral register in public situations.

Formality in Portuguese depends on context, the form of address chosen, and vocabulary. Formal tends to be more planned, courteous, and neutral; informal is closer, direct, and flexible. Adapting register is a conscious choice to communicate with clarity and respect.