We can make a zero conditional sentence with two present simple verbs. This conditional is used when the result will always happen.
If + present simple, …. present simple. **The ‘if’ in this conditional can usually be replaced by ‘when’ without changing the meaning.
If people eat too much, they get fat.
If you touch a fire, you get burned.
People die if they don’t eat.
You get water if you mix hydrogen and oxygen.
Snakes bite when they are scared
If babies are hungry, they cry
We can make the first conditional with the present simple after ‘if’, then the future simple in the result clause. It’s used to talk about things which might happen in the future.
if + present simple, … will + infinitive
If it rains, I won’t go to the park.
If I study today, I’ll go to the party tonight.
If I have enough money, I’ll buy some new shoes.
She’ll be late if the train is delayed.
She’ll miss the bus if she doesn’t leave soon.
If I see her, I’ll tell her.
We can make the second conditional with the past simple after if, then ‘would’ and the infinitive.
if + past simple, …would + infinitive
It has two uses.
1.- First, we can use it to talk about things in the future that are probably not going to be true. Maybe I’m imagining some dream for example.
If I won the lottery, I would buy a big house.(I probably won’t win the lottery)
If I met the Queen of England, I would say hello.
She would travel all over the world if she were rich.
She would pass the exam if she ever studied.(She never studies, so this won’t happen)
2.- Second, we can use it to talk about something in the present which is impossible, because it’s not true.
If I had his number, I would call him. (I don’t have his number now, so it’s impossible for me to call him).
If I were you, I wouldn’t go out with that man.
We make the third conditional by using the past perfect after ‘if’ and then ‘would have’ and the past participle in the result clause. It talks about the past. It’s used to describe a situation that didn’t happen, and to imagine the result of this situation.
If + had + past participle, …would + have + past participle
If she had studied, she would have passed the exam (but, really we know she didn’t study and so she didn’t pass)
If I hadn’t eaten so much, I wouldn’t have felt sick (but I did eat a lot, and so I did feel sick).
If we had taken a taxi, we wouldn’t have missed the plane
She wouldn’t have been tired if she had gone to bed earlier
She would have become a teacher if she had gone to university
He would have been on time for the interview if he had left the house at nine