Does "He might have done it" mean "It is possible that he did it" or "It was possible that he did it"?

Question

When we say "He might have done it", there are in my mind two possibilities:

1. we guess (a present guess) that he did it but we are not so sure of it.

2. we knew he did not do it but we want to say he had a chance to do it but he didn't do.

My question is that

Does "He might have done it" mean "It is possible that he did it" if it falls into the 1st case?

and does "He might have done it" mean "It was possible that he did it" if it falls into the 2nd case?

or in both cases it means "It is possible that he did it"?

Answer 1

Both of the interpretations you suggest are potentially correct, and are in fact used in every day speech. However, the second meaning (he did not do it in spite of being capable of doing it) is likely to be the intended meaning only if it is accompanied by additional information about why he didn't do it. For example, He might have done it, had he not been so busy, or He might have done it, but he didn't have enough money. Both of these sentences mean that he did NOT do it, a condition prevented or discouraged him from doing it, and if that condition were different it is likely he would have done it.

When used outside the context of a preventative condition, however, he might have done it is almost always intended to say there is a likelihood he did in fact do it.

Answer 2

I would say the sentence mean that

A. we think he had the possibility and

B. what we believe we know of his behaviour/mindset makes it possible that he DID do it,

e.g. means and motive.

You will need to qualify it to show the doubt:

He might have done it, but I do not think he did

There is nothing in the sentence that shows the second half of your second premise, that he did not do it.