Interrogative pronouns are words that introduce direct or indirect questions. They identify the unknown element in the sentence, such as person, thing, place, reason, manner, or quantity. In Portuguese, they typically appear at the start of the question, but they can be repeated in alternative questions. They can also be used in subordinate clauses to indicate the questioned term.

"Who" asks about the identity or function of a person or group. It can be the subject or the object in a sentence, with no gender or number variation. It keeps the same form in direct and indirect questions. It can also appear repeated for options, as in alternative questions.

"What" asks for a thing, fact, or content. It normally appears before a verb, especially in direct questions. The pronoun "que" by itself can occur with a preposition in indirect questions. In questions with the verb to be, "what" tends to introduce definitions or explanations.

"Which" asks for a selection among explicit or implicit options. It agrees in number: "which" in singular and "which" in plural. It usually appears with the verb to be when a choice or identification is expected. It can also be followed by a noun, keeping the idea of selection.

"Where" asks for a place, indicating a fixed location or reference point. It tends to be associated with verbs that express state, permanence, or existence. In standard Portuguese, it differentiates from "aonde" when there is a sense of movement with destination. "Where" can also introduce subordinate clauses that specify a location.

"Where To" asks for a destination, combining the idea of place with movement. It is formed by contracting 'a' and 'onde' and appears with verbs that require the preposition 'a'. It is typical with verbs such as 'go', 'arrive', and 'return' when there is a sense of direction. In questions, it contrasts with "where" by indicating arrival at a point, not just location.

"How" asks for a mode, manner, or procedure. It frequently appears to request explanation of a process or a result. It can introduce direct questions or, in indirect questions, connect the clause to the form of realization. In Portuguese, it does not vary in form and can combine with verbs to detail the type of mode sought.

"Why" asks for motive or reason. In general, it appears separated in direct questions, corresponding to "for what reason". It can be equivalent to "for what motive" in indirect questions, often with inversion of the order in speech. In written Portuguese, it distinguishes from "porque", which introduces explanation, and from "por quê", which can appear at the end of the sentence.

"How much" asks for quantity, value, or measure in the singular. It agrees with the noun: 'quanto' masculine singular, 'quanta' feminine singular, 'quantos' masculine plural, and 'quantas' feminine plural. It typically appears with countable or uncountable nouns, depending on meaning. In direct questions, it normally precedes the element whose measure is sought.

The main interrogative pronouns in Portuguese are "quem", "o que", "qual", "onde", "aonde", "como", "por que" and "quanto". Each one selects a type of information sought: person, thing, choice, place, destination, mode, motive or quantity. They can appear in direct or indirect questions, maintaining their function of identifying the unknown element. The agreement and the choice between forms, such as "qual/quais" and "quanto/quantos", follow the noun or the context of selection.