Which one is correct? And if both of them are correct, what is the difference?

  1. Life is a mystery
  2. Life is one mystery
  • 2
    Of these two sentences, "Life is a mystery" will be used 99% of the time, or more. But the question is interesting from a grammar standpoint. Dec 28, 2015 at 13:38
  • 2
    When you use "one", we would typically expect a modifier to follow. Life is one big mystery or ... one helluva mystery are idiomatic, as is Life is a mystery. Without a modifier, with "one", you would be invoking the idea that Life is not many separate mysteries but a unified mystery. So without a modifier is grammatical, but such a statement would have a very narrow meaning.
    – TimR
    Dec 28, 2015 at 14:05

1 Answer 1


In general, "life is a mystery" is correct.

"Life is one mystery" could be correct depending on the context. Namely:

(a) If you were saying it is not two mysteries or three mysteries, but only one. "Some people say life is made up of many mysteries. They are wrong. Life is (only) one mystery."

(b) If you were contrasting it with other mysteries. "Life is one mystery. Death is another."

There could be other cases. The point is, you would have to be making a point of the number in some way.

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