Prepositions with nouns

“In principle” or “of principle”?

In principle is a fixed expression meaning generally or theoretically. Of principle appears in phrases such as a matter of principle.

Quick answer

Which form is correct?

Use in principle to mean theoretically or in general. Do not use of principle alone. Use of principle in larger noun phrases such as a question of principle or a matter of principle.

We agree in principle.
She refused on a matter of principle.
The plan works in principle, but not in practice.

Choose the pattern by meaning

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

in principle

Meaning theoretically or generally

In principle is a fixed phrase used for general agreement or theory.

The committee accepted the idea in principle.

The design is sound in principle.

matter of principle

Referring to moral rules or values

Of principle appears after nouns like matter or question.

He objected as a matter of principle.

It became a question of principle for the board.

principled objection to

Using the adjective principled

English often uses principled to describe actions based on values.

She made a principled objection to the proposal.

They took a principled stand against corruption.

See the difference in context

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

Construction

Example

Meaning

in principle

In principle, the two sides agree.

Correct fixed expression meaning theoretically or generally.

of principle

He resigned over a matter of principle.

Correct only inside a larger noun phrase.

on principle

She refused on principle.

Correct expression meaning because of personal values.

by principle

They acted by principle.

Possible but less idiomatic than on principle or according to principle.

Common mistakes

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

Using of principle alone

English does not usually use of principle as a complete phrase.

✕ We agree of principle. ✓ We agree in principle.

Confusing principle and principal

Principle means rule or belief. Principal usually means main or head of a school.

✕ It is a matter of principal. ✓ It is a matter of principle.

Using in principle for moral motivation

For moral reasons, English often uses on principle.

✕ She refused in principle. ✓ She refused on principle.

Quick practice

Choose the expression that matches the intended meaning.

1. The company accepted the proposal ___ principle.

2. He resigned over a matter ___ principle.

3. She refused ___ principle.

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Frequently asked questions

What does in principle mean?

It means theoretically, generally, or as a basic agreement.

Is of principle correct?

Only inside larger phrases such as a matter of principle.

What is the difference between in principle and on principle?

In principle refers to theory or general agreement. On principle refers to moral beliefs or values.

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