I could use a good sleep.

[kadioguy]

I could use a good sleep.

You look like you could use a good sleep.
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What does 'could' here mean?
If I say 'can', what is the difference between them?

 

[Tdol]

I would not use can here in either sentence. Could means that on this occasion someone thinks that they or the person they are speaking to needs some sleep, but they might not get it.

 

[kadioguy]

I have found this in the OALD9:

I, you, etc. could use something
(informal) used to say that you would like to have something very much
I think we could all use a drink after that!