1. What Are Modal Verbs?

6.Conditionals

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 conditionalsplus the so-called zero conditional. There are some more conditionals that we do not use so often.

conditional type	usage	if-clause	main-clause
1	possible condition + probable result	present simple	will + base verb
2	hypothetical condition + possible result	past simple	would + base verb
3	expired past condition + possible past result	past perfect	would have + past participle
0	real condition + inevitable result	present simple	present 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:

if	condition	result
if	y = 10	2y = 20

or like this:

result	if	condition
2y = 20	if	y = 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?

if	condition	result
	Present Simple	will + base verb
If	it rains,	I will stay at home.

Read more about the First Conditional
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.