I came across this interesting question:
I know that there are already other discussions about it. But, as you know, a different context often changes a meaning of a sentence,.. and I'm struggling on MIGHT/WOULD one more time.
I wondered whether the modal "might" can have the same meaning as "would"
in the following sentences:
Lyn might have been sending texts consecutively for 15 minutes.
We saw a police helicopter overhead yesterday morning.
Really? They might have been looking for those bank robbers.
[please see the article]
I'm not sure about the first one because "might" makes me think only of something
Sir Alex Ferguson doesn't know, but he thinks possible, whereas "Would" makes me
think that the Lyn's work (sending text) had been arranged before.
Therefore Sir Ferguson expected Lyn to do that. What do you think about it?
Best Answer
SHORT ANSWER:
Might cannot be substituted for would because they express different degrees of ‘modal’ certainty.
LONG ANSWER:
May/might and will/would, like other modal verbs, have a variety of meanings, classified by linguists as deontic (having to do with obligation), epistemic (having to do with inference) and dynamic (having to do with action and intention).
But throughout these shifts in meaning, may/might and will/would exhibit a consistent contrast in modal certainty. Here are some present-tense examples.
May always signifies a possible but not certain event.
Will, on the other hand, always signifies necessity.
When modal verbs are cast in the past tense, the range of readings becomes more complex, because the past-tense forms may signify actual past tense, or present ‘tentativity’, or present counterfactuality. Combining the past-tense form with a perfect construction adds yet another layer of complexity: the perfect construction may be either a true modal perfect or a ‘sham’ perfect in which the have + Pa·Ppl is secondary tense marker which resolves the ambiguous time reference of a past-form modal. But the contrast between possibility and necessity is maintained throughout these shifts.
In your original examples the contexts make it clear that the two would have beens employ epistemic wills cast as indicatives. The first has a true modal perfect, while the second employs the perfect as a secondary tense marker.
In either case, replacing would with might would change the meaning by downgrading the sense of certainty from necessity to possibility.