Ifについての頭の整理

Zero conditional （Real condition, use present tense in both clauses）

We can talk general truth rather than specific instance of something.

Ex: If you don’t study at all, you can’t pass the exam. If you are late for your work, your boss scold you. When people smoke cigarettes, their health suffers.

一般的に極めて高い確率で起こると考えられる時はどちらも現在形。一般論を述べる場合に使う。

First conditional (Unreal, but likely)

What is said in the condition is possible. This condition refers to either present or to future time.

Ex: If I stay up late tonight, I will be tired and sleepy when I work tomorrow.

上記と異なるのは個別事象であること。まだ起っていないけどこれから起こりそうなことを話す時はMain clauseにwillを入れる。If clauseは現在形だが、「未発生」「発生確度が高いと思っている」ことを示す。起こる可能性がある＝現在・未来のことを述べる。

Second conditional (Unreal and unlikely)

What is said in the situation is unreal (impossible) or improbable situation. The tense is past, but we are talking about the present, now.

Ex: If I were a genius, I would be a mathematician or a physicist. If I were a billionaire, I would invest to some companies. 

If clauseは過去形、「未発生」、「発生確度が極めて低いと思っている」ことを示す。Main clauseはwould（couldやmight）を使う。可能性がゼロではない＝現在・未来のことについて言及している。

Third Conditional (Unreal condition)

It refers to unreal situation. We are talking about a situation that was not so in past. 

Ex: If I had had a lot money when I was a student, I would have study abroad. If I had made friends with some foreigners, I might have tried to get some chance of study abroad. 

If clauseでは過去完了。Main clauseではwould（could, mightなど）を用いる。実際に過去に起こらなかった事象をIfで述べて、Main clauseでも同様に起こらなかったことを述べる。後悔の意味合いが含まれるときも。

練習

If I were a billionaire, I would invest in stock or real estate. I wish the coronavirus would go away tomorrow. If everyone was vaccinated, we could go out soon. 

If I had not been in Tokyo, I would not have met my wife. If I had not been to America, I might not have studied English.