Macmillan says can and could show 'you are annoyed.' Then in the next two cases: what are the difference in their meaning, when we assume that both imply the narrator's annoyance?

What can you be thinking of?
What could you be thinking of?

  • I think "This question already has an answer here" is false. The linked answer doesn't discuss the nuances of "what can you be thinking of" versus "what could you be thinking of". This question only looks like a duplicate because of the title. – snailplane Feb 24 '13 at 19:41

I don't see any semantic difference between these two sentences.

[EDIT:] It's possible that can is a little more direct and suggests a rebuke because the speaker thinks the other person is thinking something odd, and that could suggests puzzlement rather than a rebuke.

In another pair that uses can and could, however, there is a difference in register:

Can you please close the door?
Could you please close the door?

The second one is slightly more polite than the first, but they both mean the same thing.

| improve this answer | |
  • Although there is no semantic difference, mightn’t there be any delicate nuance difference? – Listenever Feb 23 '13 at 9:38
  • 1
    I've added a possible nuance. – user264 Feb 23 '13 at 9:47

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