On traffic signs you see “Bridge may be icy” meaning that the bridge might be icy. Now “may” has only three letters, and highway signs don’t have much real estate, so the shorter word (ahem) might be justified. People seem to want to retreat from admitting that an event is only possible, so they use “may” to make what they say sound more polite. Or weaker. When you write expositorily—to convey information, facts, instructions, directions, or anything more formal than an email to a buddy, I recommend you be explicit—use these words precisely. Say what you mean!
May—Something has permission. You may show up any time after noon. You may watch TV after you finish your homework. You may not go out with the boys unless you bring me along.
Can—Something is able. Goats can butt. You can wash your hands and still have germs on them. You can watch TV, but it will rot your brain. I know you can fix the washing machine, but how long will it take?
Might—Something is possible. If traffic is heavy, you might be late. You might want to watch TV, but you may not, if you can’t get your work done.
You might find some room for variation, and you may certainly appeal to poetic license, but if you can, you should say exactly what you mean.
Now it’s your turn. Got any bad examples you love to hate? You may post a comment to this post and share it with us. I know you can, and some of you might. Look at the writing techniques on the right.
(Okay, no more bad rhymes.)