[General] What the different between can't and couldn't?

[Hanaka]

Hello teachers,
I wonder what the differences of these sentences: 'I can't live without it', and 'I couldn't live without it'? When should I use can't or couldn't?
I'll be very thankful for your answer or explaination. Thank you very much.
Best regards,
Hanaka

 

[BobK]

They can be similar in meaning, but the 'can't' version refers to a real situation; for example, your laptop has been being repaired for the three weeks, and you 'can't live without it'. The 'couldn't' version refers to a hypothetical situation: 'My Blackberry has all my friends' phone numbers, my 'todo' list, my email archive, photographs... - I don't know what I'd do if I lost it. I couldn't live without it.'

Of course, 'couldn't' could also (as there, without the negative prefix ;-)) be used to refer to a past instance of inability, as in: 'However hard I tried, I couldn't undo the knot.' But I don't think your question was about that sort of 'couldn't'.

b

 

[Hanaka]

Get it...thanks so much!:-D