If I see her, I will tell her.

There are several structures in English that we call conditionals or if conditionals . The word "condition" means "situation or circumstance". If  a particular condition is true, then  a particular result happens:

  • if¬†y = 3¬†then¬†2y = 6

There are three basic English conditionals plus the so-called zero conditional. There are some more conditionals that we do not use so often.

conditional typeusageif-clausemain-clause
1possible condition + probable resultpresent simplewill  + base verb
2hypothetical condition + possible resultpast simplewould  + base verb
3expired past condition + possible past resultpast perfectwould have + past participle
0real condition + inevitable resultpresent simplepresent simple

Structure of Conditional Sentences

The structure of most conditionals is very simple. There are two basic possibilities.

Of course, we add many words and can use various tenses, but the basic structure is usually like this:

ifconditionresult
ify = 102y = 20

or like this:

resultifcondition
2y = 20ify = 10

This structure can produce, for example, the following sentences:

  • If I see her, I will tell her.
  • I will tell her if I see her.

Notice the comma in the first sentence. (A comma is always correct in this case, but not always essential if the sentence is short.) In the second sentence we do not normally use a comma.

First Conditional

for real possibility

If I win the lottery, I will buy a car.

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?

ifconditionresult
 Present Simplewill + base verb
Ifit rains,I  will stay at home.

Second Conditional

for unreal possibility

If I won the lottery, I would buy a car.

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.

ifconditionresult
 Past Simplewould + base verb
IfI won  the lottery,I  would buy a car.

Third Conditional

for no possibility

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

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. :-(

ifconditionresult
 Past Perfectwould have + past participle
IfI  had won the lottery,I  would have bought a car.

Zero Conditional

for certainty

If you heat ice, it melts.

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.

ifconditionresult
 Present SimplePresent Simple
Ifyou heat ice,it melts.

Summary of Conditionals

Here is a table to help you to visualize the basic conditionals.

Do not take the 50% and 10% too literally. They are just to help you.

probability,
conditional
exampletime
100%zeroIf you heat ice, it melts.any
50%1stIf I win the lottery, I will buy a car.future
10%2ndIf I won the lottery, I would buy a car.future
0%3rdIf I had won the lottery, I would have bought a car.past
People sometimes call conditionals "if structures" or "if sentences" because there is usually (but not always) the word if in a conditional sentence.

sources : Original Link