[Grammar] can't x couldn't

[Petra J.]

Please, can you explain what is the difference between these sentences (talking about present)? I've found it in a grammar book but it's not explained there and I don't understand it.

She can't be in France.
She couldn't be in France.

I understand the first sentence but I'm really confused about the second one.

Thanks a lot.

 

[emsr2d2]

Please, can you explain what is the difference between these sentences (talking about present)? I've found it in a grammar book but it's not explained there and I don't understand it.

She can't be in France.
She couldn't be in France.

I understand the first sentence but I'm really confused about the second one.

Thanks a lot.

It's a little strange without any more context but basically "couldn't" is the past of "can't".

Today, I can't be in France because I have to be in England.

Last Friday, I couldn't be in France because I had to be in Germany.

I can't go to the cinema tonight because I will be washing my hair.

I couldn't go to the cinema last night because I was sick.

 

[Raymott]

Please, can you explain what is the difference between these sentences (talking about present)? I've found it in a grammar book but it's not explained there and I don't understand it.

She can't be in France.
She couldn't be in France.

I understand the first sentence but I'm really confused about the second one.

Thanks a lot.

You can also use "couldn't" in the present.
She couldn't be in France today. She rang me late last night from Brazil.
"Couldn't" can be used instead of "can't" if you have a condition.

You can also use it for the future:
A: Mary wants you to take her to Church tomorrow.
B: I can't do that; the minister there hates me. Anyway, I couldn't - I have to be in Paris tomorrow.
You can read an implicit condition here - "even if I wanted to".

 

[mayita1usa]

Please, can you explain what is the difference between these sentences (talking about present)? I've found it in a grammar book but it's not explained there and I don't understand it.

She can't be in France.
She couldn't be in France.

I understand the first sentence but I'm really confused about the second one.

Thanks a lot.

(Note: I'm an English teacher from the USA - what I'm going to say may not be the same in England, Australia, etc.!)

As a previous poster noted, couldn't is most often used as the past of can't.

It is difficult to explain what's really going on here without more context from you. Modals in English are often used to express different attitudes, in addition to probability or possibility - which is sometimes really difficult for non-native speakers to get. Note these two examples, which both discuss present tense situations:

She can't be in France! I need her help with my presentation today! (expresses disappointment or surprise that she is in France)

She couldn't be in France - she doesn't have a visa to enter the country. (expresses improbability or impossibility that she is in France)
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