Uncertain event + ならissue


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'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.

> 明日雨なら、うちでテレビを見ます。

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).




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.

> 明日雨なら、うちでテレビを見ます。

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).

