One of my Brazilian language partners asked me when to use which. I’m sure this has been discussed before, but I’ll try again here.
Can vs May
Can: mental/physical ability
I can reach the drawer (physical ability)
In this context, this is “conseguir” in Portuguese (Consigo alcançar a gaveta)
May: possibility; permission
The weather may change (possibility). May I sit here? (permission)
In Portuguese, “poder” is used (O tempo pode mudar) (Posso sentar aqui?)
I remember when I was in Elementary School, I asked my teacher: “Can I go to the toilet?” I should have used “may I go to the toilet?” — because of permission. She corrected me by saying:
“You can go to the toilet (physical ability) but you may not (permission)."
For Portuguese speakers, you may equate "can = conseguir" and "may = poder," but in daily conversation they are used interchangeably by English speakers, and to be honest many of them won’t know the difference. (in Portuguese, I call this QUDD: Qualquer um dos dois; either of the two is fine)
For example:
The weather can change (may should be used because of possibility)
Can I sit here? (may should be used because of permission)
But these two sentences are perfectly fine.
The subtle difference that you want to remember with regards to “permission” is that, “may" is more formal and more polite than "can." For example:
Can I sit here? (less formal, like if you’re asking your friend)
May I sit here? (more formal, like if you’re asking a stranger)
But again this is not very strict and you can use either.
May vs Might
“May" and “might" are used for “possibility" and again, QUDD, but “may” is more likely to happen and “might” is less likely to happen.
The weather may change (more likely to happen because you see the dark clouds)
The weather might change (less likely to happen because it’s very sunny, but later, maybe it might change)
Can vs Could
This is another QUDD. You can/could use either in daily conversation. To be a little strict, “could” is past tense of “can.” Look at this example:
Before, I could (past tense) run very fast, but since I sprained my ankle, I cannot (present tense).
In this instance, “can” and “could” are used as physical ability.
"Could," depending on the context, sounds more polite than "can.”
Could you pass that? (more polite) vs Can you pass that?
"Could" is also more tentative and uncertain.
I could do it (more tentative and uncertain) vs I can do it.
In summary, in normal conversations, these so called modal verbs can be used interchangeably and you really have to get worried only if there’s a grammar police nearby.
So, as we say in Portuguese, Tanto faz, Qualquer um dos dois. I doesn’t matter, either of the two (will do).
QUDD!
