I wish I may, I wish I might...

A reader asks, "May and might. I never know the correct word to use.
May I help you? I know that one BUT I might go to the store? or I may go to the store?"

Readers, I am about to let you in on one of the deep dark secrets of grammar that your English teacher never told you: There's not always a right answer.

It's true! You probably always suspected it, and now you know. The "right" answer depends on whom you ask.  I researched this a little, looking in various grammar books and web sites, because I wanted to be sure I give you my best possible answer because I just love you that much. Also because you actually care about this unlike some of the coerced guests in my classroom. So here it is.

Pay attention, class.

Traditionally, there is a subtle difference between may and might. Both are used to express the possibility of something happening, but may implies that something is quite likely, while might implies only possibility. In other words something that may happen is more likely to occur than something the might happen.

• Students may read a short story in class tomorrow.
• Tourists  might fly to the moon in my lifetime.

BUT, in actual usage, that distinction is not always observed. I daresay in everyday speech it is seldom observed. Most of the sources I checked agree that you will be correct no matter which one you use.

Several sources point out that when speaking in the past tense you must use "might have" rather than :may have".

• She might have gone to the principal's office.

So basically, in my opinion, don't worry about it. There's a very subtle difference between the two that is quickly becoming archaic and falling out of everyday usage. English is, after all, a living language and is constantly undergoing change, sort of like my waistline. 

I hope you found that useful. If I've left anything unclear please let me know, and I'll attempt to clear it up. Feel free to ask me any of your other English-teacher-type questions. But don't ask me your math questions unless you're a first grader. Just sayin'.