Interrogative adverbs introduce questions about person, place, time, manner, cause or reason. They help locate the missing information in the sentence and appear in both direct and indirect questions. In Portuguese, they do not vary in gender or number, and their interpretation depends on the function they perform in the clause.

Who asks about people and can function as subject or object of the clause. Where asks about a static place and Aonde asks about destination or direction, although the use of onde is broader in many regional varieties; for the spatial behavior of the terms, see also [Adverbs of Place] and [Interrogative Pronouns].

IdeiaIdea	ExemploExample
Quem pergunta por pessoa e pode ocupar a função de sujeito ou de objeto.Who asks about people and can occupy the function of subject or object.	Quem chegou cedo?Who arrived early?
Onde pergunta por lugar sem ideia de deslocamento.Where asks about a static place.	Onde você mora?Where do you live?
Aonde pergunta por destino ou direção.Where-to asks about destination or direction.	Aonde você vai?Where are you going?

When asking about time, moment or occasion, and it often appears in contexts related to [Adverbs of Time]. How it asks about the manner, the form or the condition in which something happens, and relates to [Adverbs of Manner].

IdeiaIdea	ExemploExample
Quando pergunta por tempo ou momento.When asking about time or moment.	Quando começa a reunião?When does the meeting start?
Como pergunta pelo modo, pela forma ou pela condição.How asks about the manner, the form or the condition.	Como você resolveu isso?How did you solve this?
Como é que é uma forma muito comum na fala coloquial.How is 'Como é que' a very common form in colloquial speech.	Como é que você fez isso?How did you do that?

Why, por quê, because and porquê belong to the same field of cause and explanation, but occupy different positions and functions in the sentence. Por que appears mainly at the beginning of the question or in indirect questions; por quê appears at the end of the question; because introduces the answer or explanation; porquê functions as a noun. The correct choice depends on the sentence structure and is a high-frequency area of confusion in writing and speaking.

IdeiaIdea	ExemploExample
Por que aparece em perguntas diretas e indiretas.Por que appears at the beginning of the question or in indirect questions.	Por que você saiu?Why did you leave?
Por quê aparece no fim da pergunta.Por quê appears at the end of the question.	Você saiu por quê?Why did you leave?
Porque introduz explicação ou resposta.Because introduces explanation or answer.	Saí porque estava cansado.I left because I was tired.
Porquê funciona como substantivo.Porquê functions as a noun.	O porquê da saída ficou claro.The reason for the exit became clear.

In direct questions, the interrogative adverb usually comes at the beginning of the sentence to mark the opening of the question. When it is governed by a preposition, the preposition can precede the adverb, as in de onde, em que or para onde, according to the syntactic requirement of the sentence. In indirect questions, the adverb appears inside the subordinate clause, as in I ask when it arrives, without the typical intonation of a direct question.

IdeiaIdea	ExemploExample
O advérbio interrogativo costuma abrir a pergunta direta.The interrogative adverb tends to open the direct question.	Quando você chega?When do you arrive?
A preposição pode aparecer antes do advérbio interrogativo.The preposition can appear before the interrogative adverb.	De onde você veio?From where did you come?
Na pergunta indireta, o advérbio fica dentro da oração subordinada.In the indirect question, the adverb stays inside the subordinate clause.	Pergunto onde ele mora.I ask where he lives.

Interrogative adverbs organize questions about people, place, time, manner and cause, and keep the same form in gender and number. Their value depends on their position in the sentence, the presence of a preposition, and the difference between direct and indirect questions. With this set, it becomes easier to recognize who, where, to where, when, how, and the four forms of porquê in reading and writing.