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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). They may be used in both direct questions (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).
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, li in Russian, czy in Polish, ?u in Esperanto, ki in Bengali, ?/? ma in Mandarin Chinese, m?/mi in Turkish, pa in Ladin, ? ka in Japanese, ko/kö in Finnish and () (da) li in Serbo-Croatian. (The English word whether has a similar function but only in indirect questions; and Multicultural London English may use "innit", even in the absence of the pronoun "it".) 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 forming questions in various languages, see Interrogative.
Interrogative words in English include:
Certain pronominal adverbs may also be used as interrogative words, such as whereby or wherefore.
For a complete list, see Category:English interrogative pro-forms on Wiktionary.
Yes-no questions can begin with an interrogative particle, such as:
English questions can also be formed without an interrogative word as the first word, by changing the intonation or punctuation of a statement. For example: "You're done eating?"
Ultimately, the English interrogative pronouns (those beginning with wh in addition to the word how), derive from the Proto-Indo-European root kwo- or kwi, the former of which was reflected in Proto-Germanic as ?wa- or khwa-, due to Grimm's law.
These underwent further sound changes and spelling changes, notably wh-cluster reductions, resulting in the initial sound being either /w/ (in most dialects) or /h/ (how, who) and the initial spelling being either wh or h (how). This was the result of two sound changes - /hw/ > /h/ before /u:/ (how, who) and /hw/ > /w/ otherwise - and the spelling change from hw to wh in Middle English. The unusual pronunciation versus spelling of who is because the vowel was formerly /a:/, and thus it did not undergo the sound change in Old English, but in Middle English (following spelling change) the vowel changed to /u:/ and it followed the same sound change as how before it, but with the Middle English spelling unchanged.
In how (Old English h?, from Proto-Germanic ?w?), the w merged into the lave of the word, as it did in Old Frisian h?, h? (Dutch hoe "how"), but it can still be seen in Old Saxon hw?, Old High German hwuo (German wie "how"). In English, the gradual change of voiceless stops into voiceless fricatives (phase 1 of Grimm's law) during the development of Germanic languages is responsible for "wh-" of interrogatives. Although some varieties of American English and various Scottish dialects still preserve the original sound (i.e. [?] rather than [w]), most have only the [w].
The words who, whom, whose, what and why, can all be considered to come from a single Old English word hw?, reflecting its masculine and feminine nominative (hw?), dative (hw?m), genitive (hwæs), neuter nominative and accusative (hwæt), and instrumental (masculine and neuter singular) (hw?, later hw?) respectively. Other interrogative words, such as which, how, where, whence, or whither, derive either from compounds (which coming from a compound of hw? [what, who] and l?c [like]), or other words from the same root (how deriving from h?).
The Proto-Indo-European root also directly originated the Latin and Romance form qu- in words such as Latin qu? ("which") and quando ("when"); it has also undergone sound and spelling changes, as in French qui "which", with initial /k/, and Spanish cuando, with initial /kw/.
Most English interrogative words can take the suffix -ever, to form words such as whatever and wherever. (Older forms of the suffix are -so and -soever, as in whoso and whomsoever.) These words have the following main meanings:
Some of these words have also developed independent meanings, such as however as an adverb meaning "nonetheless"; whatsoever as an emphatic adverb used with no, none, any, nothing, etc. (I did nothing wrong whatsoever); and whatever in its slang usage.
Interrogative pronouns in Australian Aboriginal Languages are a diverse set of lexical items with functions extending far beyond simply the formation of questions (though this is one of their uses). These pronominal stems are sometimes called ignoratives or epistememes because their broader function is to convey differing degrees of perceptual or epistemic certainty. Often, a singular ignorative stem may serve a variety of interrogative functions that would be expressed by different lexical items in, say, English through contextual variation and interaction with other morphology such as case-marking. In Jingulu, for example, the single stem nyamba may come to mean 'what,' 'where,' 'why,' or 'how' through combination with locative, dative, ablative, and instrumental case suffixes:
nyamba nyamarni manjku
IGNOR 2SG.ERG skin.name
What skin are you?
Where are we sitting?
Why are you scratching?
How will you go?
(Adapted from Pensalfini)
Other closely related languages, however, have less interrelated ways of forming wh-questions with separate lexemes for each of these wh-pronouns. This includes Wardaman, which has a collection of entirely unrelated interrogative stems: yinggiya 'who,' ngamanda 'what,' guda 'where,' nyangurlang 'when,' gun.garr-ma 'how many/what kind.'
Mushin (1995) and Verstraete (2018) provide detailed overviews of the broader functions of ignoratives in an array of languages. The latter focuses on the lexeme ngaani in many Paman Languages which can have a Wh-like interrogative function but can also have a sense of epistemic indefiniteness or uncertainty like 'some' or 'perhaps;' see the following examples from Umpithamu:
Why are you all crying for me?
yukurun ngaani yitha-n=antyampa kuura
gear IGNOR leave-PST=1PL.EXCL.NOM behind
We left some gear behind
Yupa miintha iluwa ngaani ngama-l
today good 3SG.NOM IGNOR see-IMPERF
Perhaps she is better today.
A frequent class of interrogative words in several other languages is the interrogative verb: