Is it as common to say "Why not?" to mean yes when people are asking for your permission; such as, "Can I borrow your pen?" as when replying to an invitation; such as, "Let's go to the movies"? What are the nuances of the first situation?

  • 1
    It is hard to say with statistical evidence if it is more or less common in the first situation, but it can certainly be used there. "Why not?" in this context basically just means "I do not have a reason to say no, therefore yes."
    – J. Tate
    Oct 31, 2017 at 14:50
  • Why not? can be seen as an ellipsis of (I don't see) why not?
    – Davo
    Oct 31, 2017 at 21:55

2 Answers 2


Why Not doesn't quite mean yes, but I'd say it's a synonym.

In your example:

Could I borrow your pen?

Yes would mean simply Sure, you can have my pen.

Why not means There is no reason why you can't borrow my pen.

I wouldn't say that's it's a super common response to your example question, but you could certainly say it. I think it sounds a bit more natural if you prepend it was Sure or Yea as in Sure, why not or Yea, why not. In this example, it carries the connotation of why are you even asking? or next time don't even ask, just take my pen. If this isn't what you intend to say, then I probably wouldn't use Why Not.

Personally, I would probably say something like "Yes, here you go" if I was trying to be formal and something like "Sure, no problem" or "Sure, no prob" if it was a more casual situation. That doesn't make these "correct" by any means, just what I'd personally say.


The first example is a request, so a straightforward response is appropriate. The second example is an invitation, which could reasonably be accepted with the casual 'Why not?', although it isn't very gracious.

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