Couldn't and can't

Question

Hi,

I am reading a grammar book and it said there is a difference between can't and couldn't.
Is it really important to use them according to the rules? Will native speakers know the difference of my intention if I use one of them?
We use Couldn't when we means something is impossible; Can't when we realize something is impossible; for example, I am intolerable of any noise. I couldn't sleep with the music on.
In the case, can we use I can't sleep with the music on.

Also, here are some conversations on might/ may usages that I do not have any clues how they are used.
He: I can't find Natalie. Have you seen her?
Maggie: She might be in the music room. She may be practising.
He: No, she isn't there. I thought she might be with you.
Maggie: It's a nice day. She may be on the lawn.She might be sitting out there reading the paper. Or she may be having a coffee. You might find her in the canteen.

Are they having slightly different meanings or they are just used for sentence variety.

Ryan

CalifJim · Accepted Answer

clee62can we use I can't sleep with the music on.

Yes.

I can't sleep with the music on hints that someone should turn the music off because you are trying to sleep. I can't sleep with the music on. Please turn it off.

I couldn't sleep with the music on suggests that I failed to sleep (on some previous occasion) because the music was on. Did you sleep well? No, I didn't sleep at all. I couldn't sleep with the music on.
__________________

clee62... I do not have any clues how they are used.
He: I can't find Natalie. Have you seen her?
Maggie: She might be in the music room. She may be practising.
He: No, she isn't there. I thought she might be with you.
Maggie: It's a nice day. She may be on the lawn.She might be sitting out there reading the paper. Or she may be having a coffee. You might find her in the canteen.

~~Are they having~~ Do they have slightly different meanings or ~~they are~~ are they just used for sentence variety?

For variety. There is not much difference between may and might. I see may more often in academic papers and I hear might more often in ordinary conversations. So may is slightly more formal, but its meaning is the same as might. In the examples in the conversation you quote above, both mean "It is possible that ..." in every case.

The only case to note carefully in that conversation is "I thought she might be with you". After a verb in the past (I thought that, You knew that, She said that, ...), use only might, not may.

CJ

Couldn't and can't

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