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Prepositions after adjectives

Doubtful about vs doubtful of

Both doubtful about and doubtful of are standard, but they are used in slightly different ways. About usually introduces a situation or plan, while of often expresses distrust or uncertainty about a person or thing.

Quick answer

Should you use doubtful about or doubtful of?

Use doubtful about for uncertainty about an action, idea, or outcome: doubtful about the proposal. Use doubtful of for lack of confidence in a person, claim, or possibility: doubtful of his story.

I am doubtful about the plan.
She seemed doubtful of his explanation.
They are doubtful about whether the project will succeed.

Choose the pattern by meaning

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

1
doubtful about + situation

Expressing uncertainty about a matter

Use about before plans, decisions, results, or general situations.

We are doubtful about the timing.
He felt doubtful about the proposal.
2
doubtful of + person or claim

Showing lack of confidence

Use of when questioning reliability, truth, or ability.

She was doubtful of the witness.
Many investors became doubtful of the figures.
3
doubtful whether + clause

Introducing a clause of uncertainty

Doubtful can also be followed directly by whether.

I am doubtful whether they will agree.
Scientists remain doubtful whether the method is safe.

See the difference in context

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

Construction
Example
Meaning
doubtful about
They are doubtful about the new policy.
Uncertain or hesitant about a situation or idea.
doubtful of
She is doubtful of his promise.
Not fully trusting or convinced by someone or something.
doubtful whether
I am doubtful whether we can finish today.
Introduces a clause expressing uncertainty.

Common mistakes

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

Using of with broad situations

About is usually more natural for plans, proposals, and situations.

✕ We are doubtful of the schedule change. ✓ We are doubtful about the schedule change.

Using about for distrust of a person

Of is more natural when questioning reliability or honesty.

✕ She was doubtful about the witness. ✓ She was doubtful of the witness.

Adding an unnecessary preposition before whether

Do not use about or of before whether clauses.

✕ I am doubtful about whether they will come. ✓ I am doubtful whether they will come.

Quick practice

Choose the expression that matches the intended meaning.

1. He is doubtful ___ the company's explanation.
2. We are doubtful ___ the project's future.
3. She remains doubtful ___ the deal will succeed.

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Frequently asked questions

Are doubtful about and doubtful of both correct?

Yes. Both are standard, but they emphasise different meanings and contexts.

Which is more common for plans and decisions?

Doubtful about is usually more natural with plans, ideas, and situations.

Can doubtful be followed by a clause?

Yes. Doubtful whether is a standard pattern for expressing uncertainty.

daily, for, daily, with, daily, in damaging to, for, of, in or as? damn about, near, for, to or as? "dangerous for" or "dangerous to"? "dark in", "dark for" or "dark of"? "daunting for" or "daunting to"? dead in, on, by, at or of? deadly to, in, for, of or with? "deaf to" or "deaf in"? dear to, in, for, of or as? deceased in, to, for, at or on? "decent in" or "decent for"?

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