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Prepositions with nouns

Of expert, by expert or to expert?

Expert is commonly used with in or on. By expert and of expert appear only in larger grammatical structures.

Quick answer

How to use expert with prepositions

Use expert in a subject or expert on a topic to describe knowledge. Use by an expert when naming the person who created or explained something. Of expert is uncommon except in phrases such as advice of an expert. To expert is not standard English.

She is an expert in cybersecurity.
He became an expert on climate policy.
The report was written by an expert.

Choose the pattern by meaning

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

1
expert in + field

Describing professional knowledge

Use in with broad fields, skills, or professions.

They consulted an expert in finance.
She is an expert in machine learning.
2
expert on + topic

Talking about a specific subject

Use on for specialised topics, issues, or individual subjects.

He is an expert on medieval history.
The programme featured an expert on nutrition.
3
by an expert

Naming the creator or authority

Use by to identify the expert responsible for work, advice, or analysis.

The guide was prepared by an expert.
We received an assessment by an expert.

See the difference in context

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

Construction
Example
Meaning
of expert
They requested the opinion of an expert.
Of expert alone is not idiomatic; use a larger phrase such as opinion of an expert.
by expert
The article was reviewed by an expert.
By an expert identifies the person responsible.
to expert
This combination is not standard in current English.
Use to an expert when expert is the object of the preposition.
expert in
She is an expert in data security.
Describes skill in a field.
expert on
He is an expert on trade law.
Describes knowledge about a topic.

Common mistakes

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

Using to expert without an article

English requires an article or determiner before singular countable nouns.

✕ Send the file to expert. ✓ Send the file to an expert.

Using of expert as a fixed phrase

Of expert is not a standard standalone combination.

✕ They asked of expert. ✓ They asked an expert.

Missing the article after by

Singular expert usually needs an article.

✕ The report was written by expert. ✓ The report was written by an expert.

Quick practice

Choose the expression that matches the intended meaning.

1. She is an expert ___ artificial intelligence.
2. The advice came ___ an expert.
3. Please send the documents ___ an expert.

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Frequently asked questions

Should I use expert in or expert on?

Use expert in for fields or professions and expert on for specific topics.

Is by expert correct?

Usually English says by an expert with an article.

Can I say to expert?

Not by itself. Use to an expert or to the expert.

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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