These combinations have different meanings and are not interchangeable.
Knock on and knock at both refer to hitting a door to get attention. Knock off usually means remove something by hitting it, stop working, or reduce a price.
These forms are not interchangeable. Choose the construction by meaning, not by which preposition appears most often.
Knock on is very common with doors, windows, and tables.
Knock at has a similar meaning to knock on but sounds slightly more formal.
Knock off can mean cause something to fall or stop work.
The same subject can take different constructions because each sentence answers a different question.
Some combinations appear in real text but do not mean what learners often assume.
Knock off does not mean politely tap a door.
✕ She knocked off the door. ✓ She knocked on the door.Knock at usually means repeated tapping for attention, not collision.
✕ The bike knocked at the sign. ✓ The bike knocked into the sign.Choose the expression that matches the intended meaning.
Paste the complete sentence below. Linguix checks the preposition together with grammar, spelling, punctuation, and style.
No, but it is more formal and less common than knock on.
Yes. People say We knock off at six.
Usually yes when talking about doors or windows.
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