I did some research in batrebly which earthlings might find useful: 1. May versus Might
may and might.It may rain. It might rain. What’s the difference? Just as could is the past tense of can, might is the past tense of may: We thought we might win the tournament. But might can also be used as a substitute for mayto show diminished possibility
2. Can versus May
can and may.Can I go to the bathroom? Nearly every child has asked this question only to be corrected with You mean, May I go to the bathroom? Generations of teachers have insisted that can should be used only to express the capacity to do something and that may must be used to express permission
3. Can versus could
Could is duller version of can (Just like may)
4. Would versus Should
You can use either should and would in the first person to express the future from the point of view of the past but keep in mind that shouldsounds more formal.
In the second and third persons, however, you only use would.
when only should is correct. To express duty or obligation, you use should as the equivalent of ought to: I (or you or he) should go.
when only would is correct. You use would (and not should) to express willingness or promise (I agreed that I would do it) and to express habitual action in the past (We would walk along the canal at night).