QUESTION: Is it true that the only difference between MAY and MIGHT is that MAY is stronger?
Yes, but only when we’re talking about possibilities. I may get my work done early if I don’t run into any trouble. This suggests it’s possible that I’ll finish early. Compare: If the computer screen stops freezing every five minutes, I might get this work done today. This suggests that finishing the work is a possibility but not a very strong one.
However, does the meaning change significantly in either example if we switch MAY and MIGHT? I’d argue no. In many sentences that express a low degree of likelihood, any meaning difference between these two modal verbs is so minor that students shouldn’t worry over making an incorrect choice. It’s fine to note the commonly recognized difference in degree between MAY and MIGHT, but I think what’s more important to explain is:
- MAY changes to MIGHT in reported speech to indicate something said in the past:
“I may go out later,” said Peter. – Peter said that he might go out later.
- MAY is used for permission (not MIGHT)
May I ask you a personal question?
Visitors may not park in numbered spaces. Only residents may do so.
- MAY can also be substituted with CAN in some situations. Greenbaum and Quirk note that when this is possible, CAN is considered the less formal of the two (Students should be aware of how relatively rare MAY is used in everyday spoken English.)
May/ Can I ask you a personal question?
Visitors may not/ can’t park in numbered spaces. Only residents may do so/ can.
Whales may be seen in these waters in the summer months./ Whales can be seen around here in the summertime.
- MAY, MIGHT, and COULD can all be used in to express a low degree of certainty, with the last two being favored in conversation.
You know something, you may be right./ you might be right./ you could be right.
Biber, Conrad, and Leech note that in this case, could expresses the most doubt.
 Greenbaum and Quirk. A Student’s Grammar of the English Language. Longman: 1995. P.61.
 Biber, Conrad, and Leech. Longman Student Grammar of Spoken and Written English. Pearson Education: 2002. P.179.