These questions ask whether the missing person or thing performs the action or receives it. That role determines whether the wh-expression goes directly before the verb or whether an auxiliary must come before a separate subject.
Find what is known and what is missing
Reconstruct a short statement with a blank. If the blank comes before the verb and names the doer or cause, the wh-expression replaces the subject. Keep statement order and do not add do: Something broke the latch becomes What broke the latch? The verb agrees with the wh-subject, so which plus a singular noun takes a singular verb.
If the doer is already named and the blank follows the verb, the wh-expression replaces the object. A simple-present or past object question needs do, does or did before the known subject, followed by a bare lexical verb: The guide greeted someone becomes Who did the guide greet? The same pattern applies when the missing information is an adverbial such as time or place.
| Diagnostic signal | Question pattern |
|---|---|
| The doer or cause is unknown | Wh-subject + finite verb + the rest; no do-support |
| A known subject acts on an unknown person or thing | Wh-object + do, does or did + subject + bare lexical verb |
| A known subject appears with an existing auxiliary | Wh-object + first auxiliary + subject + the rest of the verb phrase |
| A time, place or other circumstance is unknown | Treat it like the object pattern because the subject remains in the clause |
Where the wrong structures come from
- Did is added to a neutral subject question. Do-support would add emphasis or produce a malformed structure; the unknown subject already occupies the normal subject position.
- A known subject follows the wh-expression, but no auxiliary comes before it. In a simple-tense object question, supply do-support and place it before that subject.
- The two participants exchange roles. Identify who performs the action in the underlying statement before deciding whether the wh-expression is subject or object.
- Tense or agreement appears twice. After do, does or did, use the bare lexical verb; when an auxiliary is already present, invert it instead of adding do.
- An extra noun or pronoun is inserted after a wh-subject. The wh-expression already fills the missing subject slot, so the finite verb follows it directly.
- A which plus noun subject loses agreement. The head noun still controls the verb: a singular head takes a singular present form even though its identity is unknown.
Try it
Classify the role of who in 'Who did the mechanic invite to the briefing?'
- It is the subject of did.
- It is an adverb of place.
- It is a possessive determiner.
- It is the object of invite.
Select all that apply. In which scenarios should a past-simple wh-question use did?
- The guard is known; the visitor whom the guard admitted is unknown.
- The person who rang the bell is unknown.
- The team is known; the day when the team departed is unknown.
- The object that cracked the window is unknown.
Transform the source sentence 'A loose cable triggered the alarm.' into a subject question. Replace the exact fragment 'A loose cable' with what and write the complete question: ___