◆仮定法の種類は4種類あって、それぞれzero conditional, first conditional, second conditional, third conditionalと名前が付いており、用途と形式が決まっている。
We use zero conditional to talk about conditions and results which are generally or always true.
If Subject + present Verb, Subject + present Verb.
If you heat ice, it turns into water.
We use the first conditional to talk about conditions and results which are true in the future.
If Subject + present Verb, Subject + future Verb.
If we take the bus, we'll get there faster.
We use the second conditional to talk about the result of an imagined situation - one that is probably not true or probably won't happen, one that is impossible, or a situation that may only become real later.
If Subject + past Verb, Subject + would + base Verb.
If Subject + past Verb, Subject + wouldn't + base Verb.
If we stayed in such an expensive hotel, we would spend all of money in two days.
We use the third conditional to imagine how life might be different if a past situation changed or a past event didn't happen.
If Subject + past perfect, Subject + would have + past particle.
If Subject + past perfect, Subject + wouldn't have + past particle.
If you had left a little earlier, you would have caught your flight.