Can we use 青空 and 青い空 interchangeably?

Is there any difference between the two? Which is the most natural?

Thank you!

1 Answer 1


In this specific case, yes, 青空 and 青い空 both mean "blue sky". When used on their own, there is no surprising connotation and thus they are interchangeable. But 青空~ in a compound noun can mean "open-air" or "outdoor" (e.g., 青空教室 is not the same as 青い空教室).

Note that it's not always true for similar pairs. 白紙 is not the same as 白い紙, and 赤本 is not the same as 赤い本.

  • Thank you! So, hakushi means leaflet, which is not just paper that is white. And akahon is pulp fiction, not any red book. So, when we mean a color of some object, we can always use an i/na adjective + noun and never be mistaken. Am I right?
    – Enguroo
    Nov 9, 2018 at 3:27
  • 3
    @Enguroo Yes. Ah, 黒板 is different from 黒い板 just as "blackboard" is different from "black board" :-)
    – naruto
    Nov 9, 2018 at 3:29

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