Not that I know of means no, as far as I know. It's a no with an escape hatch: you haven't heard of anything like that, but you can't know everything. 'Has anyone reported a problem with the door?' 'Not that I know of.' People often add that they'll check: Not that I know of, but I'll check.
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yes-or-no question → Not that I know of.
- 'Has anyone reported a problem with the door?' 'Not that I know of.'
- 'Are there any extra fees?' 'Not that I know of, but I will check the booking details.'
- 'Is the library opening late tomorrow?' 'Not that I know of; the usual hours are still on the noticeboard.'
What changed
First version'Has the venue changed?' 'Not that I know.'
Revision'Has the venue changed?' 'Not that I know of.'
Not that I know already sounds complete, so the final of feels unnecessary. But know of means 'have heard about', and without of the reply is cut short. With of back, it's the usual answer.
I don't know is just 'no idea', with no hint of an answer. Not that I know of is closer to no than to 'no idea'. As far as I know introduces a full statement: As far as I know, the venue hasn't changed.
Your turn
Complete the established reply: 'Are any seats reserved?' 'Not that I know ___.'
Show the answer
of — The phrase ends with a preposition: not that I know of. Without of it sounds cut off.
A colleague asks whether the meeting has been moved, and nobody has told you anything. Reply in one sentence with not that I know of.
Not that I know of, but I'll check with the manager.
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