English interrogative words

The English interrogative words (also known as "wh words" or "wh forms") are words in English with a central role in forming interrogative phrases and clauses and in asking questions. The main members associated with open-ended questions are how, what, when, where, which, who, whom, whose, and why, all of which also have -ever and -soever forms (e.g., whatsoever). Those associated with closed-ended questions are whether and if.^[a]

The main role of these words is to mark a clause as interrogative. For example, How did you do it? is marked as an interrogative clause by the presence of how, and in I wonder whether it's true, whether marks the subordinate clause whether it's true as interrogative.

Extended membership

Along with the words listed above, the members include some older or archaic words, including whence, whither, and other compound prepositions such as whereby, wherein, formed from one of the central interrogative words plus a preposition.^[1]^: 686

Semantics

Semantically speaking, when used in a main clause, the interrogative words do not refer but rather question. For example, who in Who likes sewage? does not pick out a specific individual in the world, but rather asks about the identity of such an individual, should they exist. In a subordinate clause, though, this may be different. For example, how in I know how to do it, denotes a particular way of doing it rather than asking about a way.

Individual words

What is used to ask about or denote the identity of almost anything including situations (What's happening), objects (What is that thing?), and places (What city?). It cannot typically be used for persons, especially on its own. For example, What is behind that door? cannot be used to ask about a person unless it is not clear that it is a person. However, it may be used for a person's role (What is he?), and it can be combined with a noun denoting a person (What person would do that? or What child doesn't love their parents?).^[1]^{: 909–910}
Who (with its other forms whom and whose) is limited to asking about the identity of persons or denoting them.^[1]^{: 904–905}
Which is used to ask about or denote one or more members from a set.^[1]^{: 902–904}
Where is used to ask about or denote locations.^[1]^{: 905–906}
When is used to ask about or denote times.^[1]^: 905
How is used to ask about or denote manner, dispositions, and evaluations.^[1]^{: 907–909}
Why is used to ask about or denote reasons, causes, and explanations.^[1]^{: 906–907}

All of the words above may be used to ask for any number of answers. For example, Who comes on Thursday? can be asked whether the expected response is singular or plural. (For agreement purposes, though, interrogative words are singular.)

In contrast, whether and if, like other subordinators, have no semantic value, and simply mark the clause as interrogative.^[1]^: 990

Lexical categories and syntactic functions

Although the main role of interrogative words is to mark a clause as interrogative, each also has a syntactic function when used in a phrase with one or more dependents, just as any word would. For example, in What time works for you?, what functions as a determiner within the noun phrase (and interrogative phrase) what time; while in Who arrived?, who (itself a noun phrase and interrogative phrase, although it lacks dependents) functions as the subject.^[1]^: 902

Different words have different functions depending on their lexical category. For example, while a pronoun like who may typically function as a subject, a preposition like when rarely does so. Moreover, the form of the word may constrain its function. Whose (the genitive form of who), for instance, can function as a determiner, while who and whom cannot.

Individual words

Who is a pronoun.
What is a pronoun or determiner.
Which is a pronoun or determiner.
Where is a preposition.
When is a preposition.
How is usually an adverb (e.g., How rusty is it?) and sometimes an adjective (e.g., How was the movie?).^[1]^: 907
Why is an adverb.
Whether and if are subordinators.^[1]^: 990

Syntax

Interrogative words typically appear initially in interrogative clauses. It is possible, however, for adjuncts to be moved in front (Tomorrow where are you going?) and interrogative words may even appear elsewhere, as in You did what? or And you put this where? When there are two or more interrogative phrases in a single clause, only one may move to the front of the clause, as in Who said to do what? or What did who say to do? (and neither *Who what said to do? nor *What who said to do?).

Interrogative words may also be used on their own. What? for example, is often used to signal that the speaker didn't hear or understand what was said.

Interrogative vs relative words

There is significant overlap between the English interrogative words and the English relative words, but the relative words that and while are not interrogative words,^[b] and, in Standard English, what and how are mostly excluded from the relative words.^[1]^: 1053 Most or all of the archaic interrogative words are also relative words.^[1]^: 1046

Although as an interrogative word, whose is limited to denoting persons, relative whose may denote non-persons, as in a book whose cover is missing.

Notes

^ This is the if in I wonder if it will work, not the conditional if in If it works, that's great.
^ Thus the common terms "wh word" or "wh form" may be misleading.

References

^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ Huddleston, Rodney; Pullum, Geoffrey K. (2002). The Cambridge Grammar of the English Language. Cambridge: Cambridge University Press. ISBN 978-0-521-43146-0.

[1] This is the if in I wonder if it will work, not the conditional if in If it works, that's great.

[3] Thus the common terms "wh word" or "wh form" may be misleading.

[CamGEL-2] ^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ Huddleston, Rodney; Pullum, Geoffrey K. (2002). The Cambridge Grammar of the English Language. Cambridge: Cambridge University Press. ISBN 978-0-521-43146-0.

[a]

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[b]