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Prepositions after verbs

Interrogate by or interrogate for?

Interrogate normally takes a direct object. By and for usually add separate information such as agent or purpose.

Quick answer

How is interrogate used?

Use interrogate + person directly: interrogate a suspect. By may introduce the agent in passive sentences, and for may introduce a reason or topic.

Police interrogated the suspect for hours.
The witness was interrogated by detectives.
They interrogated him for details about the event.

Choose the pattern by meaning

These forms are not interchangeable. Choose the construction by meaning, not by which preposition appears most often.

1
interrogate + person

Questioning someone formally

The verb normally takes a direct object without a preposition.

Officers interrogated the driver after the accident.
2
interrogated by + agent

Showing who asked the questions

By introduces the agent in passive constructions.

The prisoner was interrogated by military officers.
3
interrogate + person + for + information

Showing the purpose of questioning

For introduces the information or reason sought.

They interrogated the witness for information about the theft.

See the difference in context

The same subject can take different constructions because each sentence answers a different question.

Construction
Example
Meaning
interrogate by
The suspect was interrogated by police.
by introduces the questioning agent
interrogate for
Detectives interrogated him for details.
for introduces the purpose or information sought
interrogate on
She was interrogated on the issue.
on introduces a topic
interrogate about
They interrogated him about the missing files.
about introduces the subject discussed

Common mistakes

Some combinations appear in real text but do not mean what learners often assume.

Adding a preposition before the person questioned

Interrogate normally takes a direct object.

✕ They interrogated to the suspect. ✓ They interrogated the suspect.

Using by in active clauses

By usually appears in passive constructions.

✕ Police interrogated by detectives the witness. ✓ The witness was interrogated by detectives.

Quick practice

Choose the expression that matches the intended meaning.

1. The officers interrogated ___ suspect overnight.
2. The witness was interrogated ___ agents.
3. They interrogated him ___ information about the case.

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Frequently asked questions

Is interrogate always formal?

Yes. It is commonly used in legal, military, or official contexts.

Can interrogate be used metaphorically?

Yes. For example, researchers may interrogate data or assumptions in academic writing.

What is the difference between interrogate and interview?

Interrogate suggests intense or formal questioning, while interview is broader and often neutral.

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