Q) It was very kind of you to do the washing up, but you -- it
Should it be "did not have to do" or "might not have done" or "must not have done"?
They all seem to convey same meaning in general to me. Which is correct grammatically?
Q) It was very kind of you to do the washing up, but you -- it
Should it be "did not have to do" or "might not have done" or "must not have done"?
They all seem to convey same meaning in general to me. Which is correct grammatically?
It was very kind of you to do the washing up, but you did not have to do it.
converts to
Your action was not necessary.
To have to is to be obliged to1.
It was very kind of you to do the washing up, but you might not have done it.
converts to
It is possible that you didn't do it.
Might is "used in auxiliary function to express permission, liberty, probability, possibility in the past"2
It was very kind of you to do the washing up, but you must not have done it.
converts to
I have come to the conclusion that you didn't do it.
Must is "used to indicate logical probability or presumptive certainty"3
1http://www.dictionary.com/browse/have-to
2http://www.merriam-webster.com/dictionary/might
3http://www.thefreedictionary.com/must