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 with one of the central interrogative words + a preposition.^[1]^: 686

Semantics

When used in a main clause, the interrogative words do no 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?).
Who is limited to asking about the identity of persons or denoting them.
Which is used to ask about or denote one or more members from a set.
Where is used to ask about or denote locations.
When is used to ask about or denote times.
How is used to ask about or denote manner, dispositions, and evaluations.
Why is used to ask about or denote reasons, causes, and explanations.

All of the words may be used to ask for any number of responses. 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 specific 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, just as any word would. For example, in What time works?, what functions as a determiner, while in Who arrived?, who 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 cannot.

Individual words

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

Interrogative vs relative words

There is significant overlap between the relative words and the interrogative words, but the relative word while is not an interrogative word,^[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

As an interrogative word, whose is limited to denoting persons, while 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 work's, that's great.
^ Thus "wh word" or "wh form" may be misleading terms.

References

^ ^a ^b ^c ^d ^e ^f ^g Huddleston, Rodney; Pullum, Geoffrey K. (2002). Cambridge grammar of the English Language. Cambridge: Cambridge University Press.

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

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

[:0-2] ^ ^a ^b ^c ^d ^e ^f ^g Huddleston, Rodney; Pullum, Geoffrey K. (2002). Cambridge grammar of the English Language. Cambridge: Cambridge University Press.

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