Tense and Conditional sentences: If/Once

Question

(a) If it began snowing, the coaches decided to cancel the game.

(b) Once it began snowing, the coaches decided to cancel the game.

Which one makes sense?

I usually use If to express a future situation. If the situation happens, it will bring the corresponding events.

I use simple present tense in the adverbial clause. As for the events, I use Will/Would to express the future tone explicitly.

According to the above description, I make some sentences.

(1) If it rains tomorrow, I will not go see a movie.

(2) If my brother passes that exam, we will give a party.

(3) If you could turn it down, I would appreciate it.

Back to my original question, I think it's perfect if I make one or two minor modifications.

If it begins snowing, the coaches will decide to cancel the game.

I'm not sure whether once has the similar usage of the tense.

I have no idea about the precise bearing of the original sentence. It uses the past tense! In what situations do such kind of past tense appear?

My question might be not loud and clear, but much appreciate if any one come up with good answers.

Answer 1

The basic difference is if is a conditional, uncertain. Once is only pointing to a given moment of time, with no uncertainty whether the event happens or not.

They will attack at dawn. If we lose... No, not if. There's thirty of them against the three of us. Once we lose, don't surrender. You don't want to learn what they do to prisoners.

In your case, of the past sentences, once (b) makes much more sense: we already know it started snowing and the coaches canceled the game. You could transfer it into a conditional: we don't know what weather was at the game, so:

If it began snowing, the coaches would have decided to cancel the game.

In your question, the phrasing should make it clear, what the coaches will do:

If it begins snowing, the coaches will cancel the game.

If it begins snowing, the coaches will decide whether to cancel the game.

Now, the decision whether to use "if" or "once" depends whether you know it will be snowing or not. "Once" means you have a sure-fire weather forecast, you know that future event. "If" means an eventuality.