What are conditionals in English grammar? Sometimes we call them 'if clauses'. They describe the result of something that might happen (in the present or future) or might have happened but didn't (in the past) . They are made using different English verb tenses.

There are four main kinds of conditionals:

• The Zero Conditional:
  (if + present simple, ... present simple)
  Eg: If you heat water to 100 degrees, it boils.


• The First Conditional:
  (if + present simple, ... will + infinitive)
  Eg: If it rains tomorrow, we'll go to the cinema.


• The Second Conditional:
  (if + past simple, ... would + infinitive)
  Eg: If I had a lot of money, I would travel around the world.


• The Third Conditional:
  (if + past perfect, ... would + have + past participle)
  Eg: If I had gone to bed early, I would have caught the train.

The Zero Conditional

We can make a zero conditional sentence with two present simple verbs (one in the 'if clause' and one in the 'main clause'):

  If + present simple, .... present simple.


  This conditional is used when the result will always happen. So, if water reaches 100 degrees, it always boils. It's a fact. I'm talking in general, not about one particular situation. The result of the 'if clause' is always the main clause.
The 'if' in this conditional can usually be replaced by 'when' without changing the meaning.


For example:

• If water reaches 100 degrees, it boils. (It is always true, there can't be a different result sometimes).
  
• If I eat peanuts, I am sick. (This is true only for me, maybe, not for everyone, but it's still true that I'm sick every time I eat peanuts)

Here are some more examples:

• 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 if they arescared.
• If babies are hungry, they cry.

The First Conditional

The first conditional has the present simple after 'if', then the future simple in the other clause:

  if + present simple, ... will + infinitive


  It's used to talk about things which might happen in the future. Of course, we can't know what will happen in the future, but this describes possible things, which could easily come true.


Here are some more examples:

• If it rains, I won't go to the park.
  
• If I study today,I will go to the party tonight.
• If I have enough money, I will buy some new clothes.
• She will be late of the train is delayed.
• She will miss the bus if she doesn't leave soon.
• If I see her, I will tell her.

The Second Conditional

The second conditional uses the past simple after if, then 'would' and the infinitive:

  if + past simple, ... would + infinitive

  (We can use 'were' instead of 'was' with 'I' and 'he/she/it'. This is mostly done in formal writing).

It has two uses.

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 wonthe lottery,I would buy a big house.
  
• If I met the Queen of England, Iwould say hello.
• She would travel all over the world if she were rich.
• She would pass the exam if she ever studied.

Second, we can use it to talk about something in the present which is impossible, because it's not true. Have a look at the examples:

• If I had her number,I would call her.
  
• If I were you, Iwouldn't go out with that person.

The Third Conditional

We make the third conditional by using the past perfect after 'if' and then 'would have' and the past participle in the second part of the sentence:

  if + past perfect, ...would + have + past participle


  It talks about the past. It's used to describe a situation that didn't happen, and to imagine the result of this situation.


Here are some more examples:

• If she had studied, she would have passed the exam.
  
• If I hadn't eaten so much,I wouldn't have felt sick.
• If we had taken a taxi, we would't have missed the plane.
• She wouldn't have been tired if she had gone to university.
• 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.