What's the difference between out of the blue and unexpectedly?

When I translate, "I apologize for calling like this, out of the blue" to French, I get Je m'excuse pour appeler comme ça, à l'improviste. When I translate that back to English, I get "I apologize for calling him that, unexpectedly."

Can I use them reversibly? Which one is the the most widely used?

  • 1
    If you want to figure out which is more widely used, you can always check Google ngrams. It's not perfect, but it often gives you a good idea.
    – user230
    Feb 20, 2013 at 2:58

1 Answer 1


"Out of the blue" is an idiom that means "unexpectedly", so yes, you can absolutely use either one! A longer (and less commonly used) version of the phrase is "Out of the clear blue sky". The idea is that it would be very unexpected if something suddenly fell from/appeared out of the sky! So that's the origin of the phrase.

I can't tell you which is more commonly used, but "out of the blue" is definitely more informal. You can use either it or "unexpectedly" and be understood easily.

(Just a side note, though Google Translate was right about the "unexpectedly", it was strange and changed your "calling like this" to "calling him that", which is not at all the same thing.)

  • 3
    As a minor addition, one alternative phrasing is bolt from the blue. I believe out of the blue is generally used like an adverb (as in, That question came out of the blue) while bolt from the blue is used like a noun (as in, That question came like a bolt from the blue).
    – J.R.
    Feb 20, 2013 at 2:20

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