I don’t think anything’s wrong with sentence 1 - なら can be used to set a condition for what follows, and that’s exactly what you’re doing, no?
Plus, I can’t help but wonder, if you need to be absolutely sure of what comes before, what’s even the point of a conditional? If you already know it’s going to rain tomorrow, I’d say using から or ので is way more logical than using なら.
EDIT: actually, Tofugu even describes the exact opposite:
you cannot use なら if the condition you are describing will definitely happen
I think what may be happening here is the sentence is ambiguous and they assume one interpretation.
Sure, you can’t be sure if it’ll rain tomorrow, so “if it rains tomorrow, I will cancel the game now” is a bit nonsensical. But that has nothing to do with なら, that goes for any conditional. You can’t act on what you don’t know.
But the way I read it, that says “if it turns out to rain tomorrow, we will cancel the game [also tomorrow]”, which is fine and in fact is exactly the intended use of なら as I see it.
Other than that, I really wouldn’t know what they’re trying to say.
This is a good point, about whether canceling the game is supposed to happen now versus tomorrow. I was thinking along the same lines, but they translate it in the book as “there will probably be no game”.
On further thought, I guess they could still mean like, “there will probably be no game TODAY”… which would be nonsensical in English too, and would solve my confusion.
I’m definitely not fluent enough (especially about producing) to be able to answer questions of correctness,
but I looked in the Dictionary of Basic Japanese Grammar and I think it’s saying that:
is saying “if it is true that it will rain tomorrow”
“tomorrow, if it rains”
So it’s the same way in English it would be odd to say “if it will rain tomorrow, the game will be canceled” as opposed to “if it rains tomorrow, the game will be canceled.” I think it’s just a subtle distinction about what exactly なら is supposing. (the kind of subtle distinction that a grammar dictionary would try to dig into).
we can verify the state “is it raining” tomorrow, but we can’t verify the state “it will rain tomorrow.” Is perhaps where their wording was going…
Nah that’s not it. The first sentence is definitely weird with the assumption that the match is tomorrow and would be rained out.
なら is this case is like assuming, in the present moment, that something is going to happen then something something. So it’s weird to use it for something in the future like the shiai in this case.
If your friend said something about how it was going to rain tomorrow, and you responded 明日雨が降るならI’ll go shopping today. I would say that’s natural and fine. But just saying their sentence as is to mean that there will probably be no game tomorrow if it rains feels wrong.
Like I said, it’s weird using it to speculate the shiai cancellation in this case. Using it for things you’ll do is fine. So I guess you could say that while I agree with the fact that sentence one is weird, I don’t agree with their explanation of why. In facf, it’s 100% bullshit. But it’s weird for other reasons.
Okay, so just to make sure I understand: if, hypothetically speaking, I were the one deciding whether there’s gonna be a game tomorrow and I’m saying 明日は雨が降るなら、試合はないでしょう, that’s fine because I’m the one making that call and I’m saying right now if I see rain tomorrow, game’s off, but if I’m not the one making that call and I’m just speculating it’s kind of weird to say that (but not so much because of なら)?
This goes exactly with what @Vanilla said, “If your friend said something about how it was going to rain tomorrow”, because in that case someone took the “burden” of deciding the future from you and affirmed “it’s going to rain tomorrow!”, so now you can actually say “Of, if that is the case, I will 〇〇”