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Prepositions after adjectives

Unfaithful to, in, with, at or by?

Unfaithful to is the standard expression for disloyalty in relationships, promises, or beliefs.

Quick answer

Which preposition is correct with unfaithful?

Use unfaithful to for a person, commitment, or principle. Other prepositions usually belong to separate parts of the sentence rather than to the adjective itself.

He was unfaithful to his wife.
The film remains unfaithful to the original novel.

Choose the pattern by meaning

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

1
unfaithful to + person

Talking about romantic or personal disloyalty

To introduces the person someone betrays or does not remain loyal to.

She admitted being unfaithful to her partner.
He stayed unfaithful to his vows.
2
unfaithful to + source/idea

Talking about inaccurate representation

The phrase can describe something that does not stay true to an original work or principle.

The adaptation is unfaithful to the book.

See the difference in context

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

Construction
Example
Meaning
unfaithful to
He was unfaithful to his spouse.
disloyal or not faithful
unfaithful in
She was unfaithful in her marriage.
in her marriage describes the context, not the complement of unfaithful
unfaithful with
He was unfaithful with a colleague.
with introduces the other person involved, not the person betrayed
unfaithful at
He was unfaithful at a difficult time.
at a difficult time is a time adjunct
unfaithful by
The translation is unfaithful by modern standards.
by modern standards is an adjunct of evaluation

Common mistakes

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

Using with for the betrayed person

Use to for the person or commitment that receives loyalty.

✕ He was unfaithful with his wife. ✓ He was unfaithful to his wife.

Using in as the main complement

In usually introduces context, not the object of loyalty.

✕ She was unfaithful in her husband. ✓ She was unfaithful to her husband.

Quick practice

Choose the expression that matches the intended meaning.

1. He was unfaithful ___ his partner.
2. She was unfaithful with a colleague. Here, with refers to ___.
3. The movie is unfaithful ___ the original story.

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Frequently asked questions

What is the standard preposition after unfaithful?

Use to: unfaithful to someone or something.

Can I say unfaithful with someone?

Yes, but with refers to the person involved, not the person betrayed.

Can unfaithful describe books or films?

Yes. A version can be unfaithful to the original work.

ubiquitous in, on, across, throughout or for? "ugly in", "ugly for" or "ugly of"? ultimate in, of, for, on or as? "unacceptable to", "unacceptable in" or "unacceptable for"? unaccounted for unaccustomed to or in? unacquainted with unaffected by, in, for or with? "unaffordable for" or "unaffordable to"? unanimous in, on, about, regarding or for? "unattractive to" or "unattractive for"? "unavailable for" or "unavailable to"?

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