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Prepositions with nouns

"On duty" vs. "of duty"

"On duty" is the standard English expression for someone currently working or responsible for a task. "Of duty" is not a normal modern combination.

Quick answer

Which phrase is correct?

Use "on duty" when someone is working, serving, or responsible at a particular time. "Of duty" is generally not idiomatic in modern English except inside larger expressions such as "sense of duty."

A nurse is always available on duty at night.
Who is on duty today?
He acted out of a strong sense of duty.

Choose the pattern by meaning

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

1
on duty

Showing active work responsibility

Use "on duty" for someone currently working or officially responsible.

Two officers are on duty tonight.
The manager was still on duty after midnight.
2
off duty

Showing someone is not working

"Off duty" is the opposite of "on duty."

The doctor is off duty this weekend.
She avoids work calls when off duty.
3
sense of duty

Talking about responsibility or obligation

Use "of duty" inside fixed noun phrases such as "sense of duty."

He stayed because of his sense of duty.
Their feeling of duty was very strong.

See the difference in context

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

Construction
Example
Meaning
on duty
A firefighter is on duty all night.
Standard expression for active service or work.
of duty
He has a strong sense of duty.
Appears only inside larger noun phrases, not as a replacement for "on duty."
off duty
The officer is off duty today.
Not currently working.
duty for
She volunteered for duty at the clinic.
Different structure showing assignment or purpose.

Common mistakes

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

Using "of duty" for work status

English uses "on duty" for active responsibility.

✕ The guard is of duty. ✓ The guard is on duty.

Forgetting the opposite form

Use "off duty" when someone is not working.

✕ She is not on duty now. ✓ She is off duty now.

Using "in duty"

"In duty" is not a normal modern expression.

✕ The nurse is in duty. ✓ The nurse is on duty.

Confusing "duty" with "job"

"On duty" refers to responsibility status, not just employment.

✕ I am on duty at a bank employee. ✓ I work at a bank.

Quick practice

Choose the expression that matches the intended meaning.

1. The receptionist is ___ until 6 p.m.
2. The pilot is ___ this weekend.
3. He stayed late because of his strong ___

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Frequently asked questions

Is "of duty" ever correct?

Yes, but usually only inside larger phrases such as "sense of duty" or "feeling of duty."

What does "on duty" mean?

It means someone is currently working or officially responsible.

Can I say "at duty"?

No. Modern English normally uses "on duty."

of, about, against, to or for racism? of, about, for, in or on friendship? of, about, for, on or to thing? of, about, for, to or with sex? of, about, on, to or for moon? "of access" or "with access"? "of accommodation" or "for accommodation"? "of accuracy" or "for accuracy"? "of action" or "in action"? "of actor", "with actor" or "by actor"? "of address" or "to address"? "of administration" or "in administration"?

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