3rd person verb (base verb) after what/who

If your sentence reads "What she do next?" or "Who they call yesterday?" the auxiliary that shows tense and agreement is missing. Add does (present third-person) or did (past), or use the existing auxiliary/modal (is, have, can, will) and keep the main verb in base form.

Quick answer: when to add does or did

If a what/who question has no auxiliary or modal, use does for present third-person singular (he/she/it) and did for past. If an auxiliary/modal is already present, keep it and use the main verb in base form.

Present, third-person: What does she do? (not What she do?)
Past (any subject): Who did they call yesterday? (not Who they call yesterday?)
If an auxiliary exists: What is she doing? / What can he do?

Core explanation: what's actually wrong

English forms questions with auxiliaries when no other helper is available. The auxiliary carries tense and subject agreement; the main verb remains in base form. Dropping the auxiliary leaves the sentence without tense or agreement and sounds ungrammatical.

No auxiliary? Add do/does/did + base verb.
Present, third-person singular → does + base verb.
Past (all subjects) → did + base verb.

Present and past question formation (brief grammar)

Use these templates and substitute the subject and verb base form:

Present (3rd person): What/Who + does + subject + base verb + ? → What does he want?
Present (other persons): What/Who + do + I/you/we/they + base verb + ? → What do they want?
Past (all persons): What/Who + did + subject + base verb + ? → What did she say?

Wrong: What she wants for dinner?
Right: What does she want for dinner?
Wrong: Who you invite to the meeting?
Right: Who did you invite to the meeting?

Examples: realistic wrong/right pairs

Incorrect sentence first, corrected second. Grouped for quick scanning.

Wrong: What she do next? -
Right: What does she do next?
Wrong: Who they call yesterday? -
Right: Who did they call yesterday?
Wrong: What the report say? -
Right: What does the report say?
Wrong: Who know the answer? -
Right: Who knows the answer?
Wrong: What she study in college? -
Right: What did she study in college?
Wrong: What they submit for the audit? -
Right: What did they submit for the audit?
Wrong: Who you bring to the party? -
Right: Who did you bring to the party?
Wrong: What the professor assign? -
Right: What did the professor assign?
Wrong: Who approve the budget? -
Right: Who approves the budget?
Wrong: What they say about the movie? -
Right: What did they say about the movie?
Wrong: What he do for a living? -
Right: What does he do for a living?
Wrong: What she do yesterday night? -
Right: What did she do last night?

Rewrite help: quick templates and ready repairs

Follow this short checklist: 1) Is there already an auxiliary/modal? If yes, keep it. 2) If present + third-person singular → add does. 3) If past → add did.

Present (3rd): What does + [subject] + [base verb] + ?
Past: What did + [subject] + [base verb] + ?
With modal/auxiliary: What + [auxiliary/modal] + [subject] + [verb] + ? (e.g., What can she do?)

Rewrite:
Wrong: "What she do next?" →
Correct: "What will she do next?" or "What does she do next?"
Rewrite:
Wrong: "Who they call yesterday?" →
Correct: "Who did they call yesterday?"
Rewrite:
Wrong: "What the client want from us?" →
Correct: "What does the client want from us?"
Rewrite:
Wrong: "Why she not come?" →
Correct: "Why didn't she come?"
Rewrite:
Wrong: "Who you ask about this?" →
Correct: "Who did you ask about this?"

Memory trick: three things to hear while you write

Say the sentence aloud and listen for the helper word that carries tense.

If you hear present third-person: insert does before the subject.
If you hear past: insert did before the subject.
If you already hear an auxiliary or modal (is/has/can/will), keep it and use the base verb.

Tip: Read "What does she want?" aloud - the does makes the present tense obvious.

Try your own sentence

Test the whole sentence in context; that usually shows which auxiliary fits.

Real usage: formal vs casual tone and contractions

In formal writing-reports, emails, exams-always include the auxiliary. Casual speech and chat may reduce or contract auxiliaries, but those forms can look wrong in professional text.

Formal: use full auxiliaries (does/did).
Informal: contractions like "What'd he say?" are common in speech; prefer "What did he say?" in writing.
Emphatic uses of does (Who does know the answer?) are stylistic and rare.

Hyphenation and spacing: small formatting rules that matter

Hyphens don't affect auxiliary choice, but use them correctly in compound modifiers and keep standard spacing around punctuation.

Hyphenate compound modifiers before a noun (third-person question), not inside the question itself.
End direct questions with a question mark and use a single space after it.
Capitalize the next sentence as usual.

Context templates: ready examples for work, school, and casual use

Pick a template, plug in the subject and base verb, and you have a ready sentence.

Work (present): What does the client want from us? / Who approves the budget?
Work (past): What did the team deliver last sprint? / Who did we brief about this?
School: What did the professor assign for Week 3? / Who knows the answer to problem 4?
Casual: Who did you bring to the party? / What did they say about the show?

Examples: Wrong: "What the client want from us?" →
Right: "What does the client want from us?"
Examples: Wrong: "What she study in college?" →
Right: "What did she study in college?"
Examples: Wrong: "Who you bring?" →
Right: "Who did you bring?"

Similar mistakes to watch for

Fixing auxiliaries often clears up these related errors.

Negative questions: "Why she not come?" → "Why didn't she come?" or "Why did she not come?"
Double marking: "Does she knows?" → "Does she know?"
Statement vs question: "She do her job" → "She does her job" (statement) or "Does she do her job?" (question)

Wrong: Does she knows the plan? -
Right: Does she know the plan?
Wrong: Why she not come? -
Right: Why didn't she come?

FAQ

Why "What does he do?" instead of "What he do?"

Because English needs an auxiliary (does) to form a present-simple question for third-person subjects when no other auxiliary or modal is present. The auxiliary shows tense and agreement; the main verb stays in base form.

Is "Who knows the answer?" correct or should it be "Who do know the answer?"

"Who knows the answer?" is correct. When who functions as the subject, the verb takes -s in present simple. You only add does when forming an auxiliary question, emphasis, or a negative form.

Can I use contractions like "What'd he say?"

Contractions like "What'd he say?" are fine in informal speech or chat. In formal writing, use the full form "What did he say?"

How should I fix "What she do next?" in a professional email?

Choose the tense you mean. For future intent: "What will she do next?" For present routine: "What does she do next?" Both include an auxiliary and match different meanings.

What's a quick edit checklist to spot this error?

Ask: Do I hear an auxiliary/modal? If no, is the question present + third-person? add does. Is it past? add did. If you already see is/has/can/will, keep it and use the base verb.

Quick test: paste one sentence to check

If you still doubt which auxiliary fits, rephrase using the templates above or paste the full sentence into a checker. Usually adding the correct auxiliary is the single fix needed.