Basically, the title says it all. When should you use “might” and when should you use “may”, or, are they, for all intents and purposes, interchangeable?
Here’s an example:
The operation might not be necessary if the medicine works.
OR
The operation may not be necessary if the medicine works.
Actual usage is all over the place and generally speaking the two are interchangeable (I believe they originated as different tenses of the same word), but my personal preference is to use “might” to indicate a possibility and “may” in the instance of permission.
That’s reminiscent of saying “yes, you can” when you’re affirming that someone is capable of something, and “yes, you may” when you’re giving them permission to do so. That notwithstanding, do you really think it applies to might/may, too?
Just to illustrate how I distinguish them:
– I might go to see a movie tonight = There is a possibility that I will go to see a movie tonight.
– I may go to see a movie tonight = I have been granted permission to go see a movie tonight.
Checking the dictionary, though –
(1) The entry for “may” lists the possibility connotation before the permission one.
(2) In the present and future tense, “may” becomes “might.”
So the distinction I make seems to be purely a personal preference.
But there are times when there is a significant difference between the two. For example, the following two sentances have totally different meanings. (1) When he fell down, he might have been hurt. (2) When he fell down, he may have been hurt. In the first instance, it could have happened, the possibility was there, but he was lucky and it didn’t. In the second, we don’t know whether or not it happened, maybe he was hurt, maybe he wasn’t.
I don’t see your reading of the distinction as one that is reflected by actual usage. I would probably use the words in the way that you do, but it seems just as arbitrary and idiosyncratic as the one I make.