Interrogative word

An interrogative word or question word is a function word used to ask a question, such as what, which, when, where, who, whom, whose, why, whether and how. They are sometimes called wh-words, because in English most of them start with wh- (compare Five Ws). Most may be used in both direct (Where is he going?) and in indirect questions (I wonder where he is going). In English and various other languages the same forms are also used as relative pronouns in certain relative clauses (The country where he was born) and certain adverb clauses (I go where he goes). It can also be used as a modal, since question words are more likely to appear in modal sentences, like (Why was he walking?)

A particular type of interrogative word is the interrogative particle, which serves to convert a statement into a yes–no question, without having any other meaning. Examples include est-ce que in French, ли li in Russian, czy in Polish, чи chy in Ukrainian, ĉu in Esperanto, āyā آیا in Persian, কি ki in Bengali, 嗎/吗 ma in Mandarin Chinese, mı/mi/mu/mü in Turkish, pa in Ladin, か ka in Japanese, 까 kka in Korean, ko/kö in Finnish, Kasi (or "Ka" for short) in Tumbuka, tat in Catalan, (да) ли (da) li in Serbo-Croatian and al and ote in Basque. "Is it true that..." and "... right?" would be a similar construct in English. Such particles contrast with other interrogative words, which form what are called wh-questions rather than yes–no questions.

For more information about the grammatical rules for using formed questions in various languages, see Interrogative.

Interrogative words in English can serve as interrogative determiners, interrogative pronouns, or interrogative adverbs. Certain pronominal adverbs may also be used as interrogative words, such as whereby or wherefore.

The interrogative words which, what and whose are interrogative determiners when specifying a noun or nominal phrase: The question Which farm is the county’s largest? specifies the noun farm as definite, while What farm? is indefinite. In the question Whose gorgeous, pink painting is that?, whose is the interrogative, personal, possessive determiner prompting a specification for the possessor of the noun phrase gorgeous pink painting.

The interrogative words who, whom, whose, what and which are interrogative pronouns when used in the place of a noun or noun phrase. In the question Who is the leader?, the interrogative word who is a interrogative pronoun because it stands in the place of the noun or noun phrase the question prompts (e.g. the king or the woman with the crown). Similarly, in the question Which leads to the city center? the interrogative word which is an interrogative pronoun because it stands in the place of a noun or noun phrase (e.g. the road to the north or the river to your east). Note, which is an interrogative pronoun, not an interrogative determiner, because there is no noun or noun phrase present to serve as a determiner for. Consequently, in the question Which leads to the city center? the word which is an interrogative pronoun; when in the question Which road leads to the city center? the word which is an interrogative determiner for the noun road.

The interrogative words where, when, how, why, whether, whatsoever, and the more archaic whither and whence are interrogative adverbs when they modify a verb. In the question How did you announce the deal? the interrogative word how is an interrogative adverb because it modifies the verb did (past tense of to do). In the question Why should I read that book? the interrogative word why is an interrogative adverb because it describes the verb should.

Note, in direct questions, interrogative adverbs always describe auxiliary verbs such as did, do, should, will, must, or might.