Can or May? Could or might?

Hello everybody.

In my last English class, my teacher asked us to solve this exercise about Modal Verbs:

Rewrite the sentences by changing the verbs to a modal verb:

1 - It's up to Carla to send the invitations. All her guests are all right for me.
My answer was: Carla can invite anybody she wants.
But my teacher told me that "can" sounds quite informal and that "may" must be used in this sentence.
I'd like to know your opinion about this.
Is "can" that rude in this sentence? Why should I use "may"?

The other doubt appeared in this exercise:

2 - Your brother had my permission to use my computer.
My answer: Your brother could use my computer.
But again my teacher said that I should use "might" instead of "could". She affirmed that "might" is the past form of "may" and that "could" wouldn't fit very well in this sentence.
What is your opinion about this one? Doesn't "might" sound a bit weird in this sentence?

I'd really appreciate your help.

Adailton

Oliveira,

Your teacher is teaching you a formal style. The majority of people in the U.S., myself included, would say "can" and "could" in informal situations. I see nothing wrong with your original sentences.

Naturalmente, se a tua professora quiser um estilo mais formal, uses "may" e "might.".....mas na nossa vida diária, usamos mais "can" e "could."

Yes mjd, I understand that...

What if I was given a university entrance exam and I had to choose whether "may" or "can" and "could" or "might" in those sentences. Which should I opt? Would both be right?

Well, as a Briton I'd give my opinion.... (but I'm no English teacher)



---------------------------------------------
1 - It's up to Carla to send the invitations. All her guests are all right for me.
My answer was: Carla can invite anybody she wants.
---------------------------------------------

I see nothing wrong with 'can' here.

Carla may invite
Carla can invite (they both mean the same thing when it comes to this)


---------------------------------------------
Your brother had my permission to use my computer.
My answer: Your brother could use my computer.
---------------------------------------------

I see nothing wrong with 'could' too.

Using might is surely wrong?

"Might" is a conditional statement.

"John might have used my computer."....then again he might not have.

When taking an exam, opt for the formal answer, but I wouldn't use "might" in the second sentence.