Zero Conditional: certainty

We use the so-called zero conditional when the result of the condition is

always true, like a scientific fact.

Take some ice. Put it in a saucepan. Heat the saucepan. What happens? The ice
melts (it becomes water). You would be surprised if it did not.

IF condition result

  present simple present simple

If you heat ice it melts.

Notice that we are thinking about a result that is always true for this condition.
The result of the condition is an absolute certainty. We are not thinking about
the future or the past, or even the present. We are thinking about a simple fact.
We use the present simple tense to talk about the condition. We also use the
present simple tense to talk about the result. The important thing about the
zero conditional is that the condition always has the same result.

We can also use when instead of if, for example: When I get up late I miss my

bus.

Look at some more examples in the tables below:

IF condition result

  present simple present simple

If I miss the 8 o'clock bus I am late for work.

If I am late for work my boss gets angry.

If people don't eat they get hungry.

If you heat ice does it melt?

 
result IF condition

present simple   present simple

I am late for work if I miss the 8 o'clock bus.

 My boss gets angry if I am late for work.

People get hungry if they don't eat.

Does ice melt if you heat it?

First Conditional: real possibility

We are talking about the future. We are thinking about a particular condition or
situation in the future, and the result of this condition. There is a real possibility
that this condition will happen. For example, it is morning. You are at home.
You plan to play tennis this afternoon. But there are some clouds in the sky.
Imagine that it rains. What will you do?

IF condition result

  present simple WILL + base verb

If it rains I will stay at home.

Notice that we are thinking about a future condition. It is not raining yet. But
the sky is cloudy and you think that it could rain. We use the present simple
tense to talk about the possible future condition. We use WILL + base verb to
talk about the possible future result. The important thing about the first
conditional is that there is a real possibility that the condition will
happen. Here are some more examples (do you remember the two basic
structures: [IF condition result] and [result IF condition]?):

IF condition result

  present simple WILL + base verb

If I see Mary I will tell her.

If Tara is free tomorrow he will invite her.

If they do not pass their exam their teacher will be sad.

If it rains tomorrow will you stay at home?

If it rains tomorrow what will you do?

 
result IF condition

WILL + base verb   present simple

I will tell Mary if I see her.

He will invite Tara if she is free tomorrow.

Their teacher will be sad if they do not pass their exam.

Will you stay at home if it rains tomorrow?

What will you do if it rains tomorrow?

Second Conditional: unreal possibility or dream

The second conditional is like the first conditional. We are still thinking about
the future. We are thinking about a particular condition in the future, and the
result of this condition. But there is not a real possibility that this condition will
happen. For example, you do not have a lottery ticket. Is it possible to win? No!
No lottery ticket, no win! But maybe you will buy a lottery ticket in the future.
So you can think about winning in the future, like a dream. It's not very real,
but it's still possible.

IF condition result

  past simple WOULD + base verb

If I won the lottery I would buy a car.

Notice that we are thinking about a future condition. We use the past simple
tense to talk about the future condition. We use WOULD + base verb to talk
about the future result. The important thing about the second conditional is
that there is an unreal possibility that the condition will happen.

Here are some more examples:

IF condition result

  past simple WOULD + base verb

If I married Mary I would be happy.

 If Ram became rich she would marry him.

If it snowed next July would you be surprised?

If it snowed next July what would you do?

 
result IF condition

WOULD + base verb   past simple

I would be happy if I married Mary.

She would marry Ram if he became rich.

Would you be surprised if it snowed next July?

What would you do if it snowed next July?

Third Conditional: no possibility

The first conditional and second conditionals talk about the future. With
the third conditional we talk about the past. We talk about a condition in the
past that did not happen. That is why there is no possibility for this condition.
The third conditional is also like a dream, but with no possibility of the dream
coming true.

Last week you bought a lottery ticket. But you did not win. :-(

condition result

  Past Perfect WOULD HAVE + Past Participle

If I had won the lottery I would have bought a car.

Notice that we are thinking about an impossible past condition. You did not win
the lottery. So the condition was not true, and that particular condition can
never be true because it is finished. We use the past perfect tense to talk about
the impossible past condition. We use WOULD HAVE + past participle to talk
about the impossible past result. The important thing about the third conditional
is that both the condition and result are impossible now.
Sometimes, we use should have, could have, might have instead of would
have, for example: If you had bought a lottery ticket, you might have won.

Look at some more examples in the tables below:

IF condition result

  past perfect WOULD HAVE + past participle

If I had seen Mary I would have told her.

If Tara had been free yesterday I would have invited her.

If they had not passed their exam their teacher would have been sad.

If it had rained yesterday would you have stayed at home?

If it had rained yesterday what would you have done?

 
result IF condition

WOULD HAVE + past participle   past perfect

I would have told Mary if I had seen her.

I would have invited Tara if she had been free yesterday.

Their teacher would have been sad if they had not passed their exam.

Would you have stayed at home if it had rained yesterday?

What would you have done if it had rained yesterday?