I'm studying なら conditional form now and cannot understand the following: In a "Dictionary of basic japanese grammar" there is a note that s1ならs2 (s=sentence) could not be used when: 1) s1 never fails to occur; 2)one can never tell whether s1 condition is true or false and 3) when the speaker already knows that s1 is true.

The question is connected to the 2nd rule. There is an example (of what is deemed wrong and ungrammatical according to 2nd rule): あした雨が降るなら試合はないでしょう。 It is said that one could never tell whether tommorow will be rain or not. However, on Internet I have found a next example which is considered grammatical, as I've understood: 明日雨なら、うちでテレビを見ます。

Both of them are connected to the uncertain future event, and it is impossible for the speaker to determine will the rain happen or not... Then what is the difference? Is it the use of Verb before なら which makes the first construction wrong?

Please help :)

  • I don't understand why the first sentence doesn't comply with the second rule. You can't be sure that il will rain tomorrow so there is uncertainty. I'd like to help you but I don't see what part you don't understand.
    – N Gillain
    Commented Jan 25, 2019 at 15:50
  • The first sentence is an example given in the "Vocabulary", not created by me. It is said in this book that the one could not be certain whether there will be rain or not tomorrow, and hence the sentence is deemed ungrammatical by author. And the second sentence from internet implies the same thing - "if it rains tomorrow", but is deemed grammatical. They are both dealing with the uncertain event, but I can't find the difference which makes first sentence ungrammatical and the second one grammatical :(
    – Vic Zhi
    Commented Jan 25, 2019 at 16:28
  • The only anwser I have for myself for now is that, maybe, the first sentence implies the meaning of "if it rains tomorrow"(and we don't know if it is true untill tomorrow), and the second one implies the meaning "if tomorrow rain is the thing we are talking about"(as a supposition of the fact)...
    – Vic Zhi
    Commented Jan 25, 2019 at 16:45

1 Answer 1


I'm not 100% sure about this, but this is my feeling.

x あした雨が降るなら試合はないでしょう。

This sentence conforms to rule 2). The speaker doesn't know if it will rain tomorrow. We can tell this because of でしょう at the end. So the sentence is ungrammatical.


In this sentence, perhaps the speaker has seen the weather forecast and is almost certain that it will rain tomorrow. The speaker is assuming that it will rain tomorrow and, if that's the case, they'll watch TV at his house. Whereas, in the first sentence there is no assumption that it will rain, it is just trying to say what might happen if it rains (ungrammatically).

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