"acknowledgement" or "recognition"?

Years ago I wrote an essay on aggressiveness and one of my sentences was "a strong defence against the outside world can be an acknowledgment of internal human failure..." My teacher then crossed out "acknowledgement" and wrote "recognition". When I asked him why he had done it, he just said "recognition was the right word for that context". I wasn't convinced and perhaps that's why I still remember it.

Definitions for "acknowledgment" (or acknowledgement) from mainstream dictionaries:

• recognition of the importance or quality of something. ODO
• recognition or notice. TFD
• the fact of accepting that something is true or right CDO

In the above context, I can't see any difference between the two words to this day. My question is, are they interchangeable? Is there any subtlety I have missed?

The difference (and there is one) is that you can recognize something without acknowledging it. Acknowledgement implies the external admission of a fact, whereas recognition may only be internal.

Think of it this way: I can recognize your contribution without acknowledging it. If I acknowledge your contribution, it presupposes that I am communicating it to (at least) another party, which may not include you. That's not true 100% of the time: I may acknowledge your contribution, but only to myself. Still, acknowledgment seems to need an audience, if only (as a last resort) an internal one. Recognition may happen whether one is conscious of the process on that "meta" level or not.

Example

John recognized Mary's contribution to the team, but refused to acknowledge it publicly lest she garner too much of what he felt should be his credit alone. Mary would receive no public recognition from the committee during her tenure there.