I've been confused about this ever since I started to learn Japanese: What is
the correct verb tense for sentences like "If I had known ... then I would
have"?

Concrete example:

If I had known that (it was not going to be so hot today) I would've joined
the competition.

My attempt:

それを分かったら、大会に出る。

I've been stuck for words in this situation lots of times.
CC BY-SA 3.0
2015-07-26T09:15:36.103
25951
2016-06-18T02:41:56.813
10344
question
grammar
Correct verb tenses for if-would-type sentences
Since you are talking about things past, you should use past tense.

それを分かっていたなら、大会に出ていた。  
or  
それが分かっていたら、大会に出ていた。

If you say "それ **が** 分かったら、大会に出る。" (Quick grammar fix を -> が) it sounds like
you are talking about the future. Which means you haven't know it (it's going
to be so hot or not) but you will know it later. And you will decide to join
the competition depending on it.

** Description on the quick grammar fix **

I fixed grammar それを -> それが, but one of my answer is それを... Here is the reason
why.

First off, the full sentences of my two answers are:  
**私が** それを分かっていたなら、大会に出ていた。  
それが **私に** 分かっていたら、大会に出ていた。  

The two sentences have almost the same meaning, but the nuance is different.
The subject of the first sentence is 私, so the sentence focus on 私 weather or
not know about それ (it's going to be so hot or not). Which has nuance that
speaker (it is equals to 私 in this case) know someone who know about それ. That
means, 私 didn't know what the weather going to be before the competition, but
now 私 knows.

The subject of the second sentence is それ. It has extra nuance that 私 might has
other information (like where the competition held, how many people are
joining it, etc) but それ (it's going to be hot or not) is the important to make
decision.

Now, get down to your phrase. The full sentence of "それ **を** 分かったら、大会に出る。" is:  
**私が** それを分かったら、大会に出る。  
Since 私 is a subject, it sounds like speaker (the speaker is equal to 私 in
this case) know someone who know about それ. If so, 私 usually don't speak like
that. Maybe "それを聞いてから決めます。" (I'll make decision after I heard it.)

The full sentence of それが分かったら、大会に出る。 is:  
それが **私に** 分かったら、大会に出る。  
Which has extra nuance you know some other information, but what you need make
decision to join competition is それ.
CC BY-SA 3.0
2015-07-26T11:01:09.217
25952
2016-06-18T02:41:56.813
2016-06-18T02:41:56.813
11104
9608
25951
answer
I think you could say:

> (もし)それが分かっていたら/いれば、大会に出たのに。  
>  ～～、大会に出ていたのに。  
>  ～～、大会に出ていただろう(に)。  
>  ～～、大会に出たんだけど(なぁ)。  
>  ～～、大会に出ていたんだけど(なぁ)。  
>  etc.

Example:

> (もし)彼女の電話番号を知ってたら/れば、電話したのに。/してたのに。/してただろう(に)。/したんだけど(なぁ)。etc.  
>  (If I had known her phone number, I would have called her.)

Compare:

> (もし)彼女の電話番号を知ってれば/たら、電話 **する** のに。/ **する** だろう(に)。/ **する** んだけど(なぁ)。etc.  
>  (If I knew her phone number, I would call her.)
CC BY-SA 3.0
2015-07-27T01:19:56.607
25958
2015-07-27T01:19:56.607
9831
25951
answer