Zero, First, Second and Third Conditional

2. A conditional is a sentence or part of a sentence that expresses a condition. It usually
begins with the words “when,” “if,” and “unless.”
A condition is what must happen before something else can happen.
She would tell me if she knew.
(She doesn’t know.)
They will come when I call them.
(They will not come before I call them.)
I will sleep now unless I have sleeplessness.
(I will not sleep if I have sleeplessness.)
There are four basic conditionals in English.

3. We use the zero conditional when talking about things which are always true, or
generally true.
"If the sun sets, it becomes night."
Structure:
If + Simple Present, + Simple Present
If you boil an egg, it becomes solid.
OR
Simple Present + If + Simple Present
I always listen to music if I jog.
Note: We can use "when" instead of "if."
When you boil an egg, it becomes solid.
I always listen to music when I jog.

4. We use first conditional when talking about possible future events.
"If he catches a fish, he will be very happy."
Structure:
If + Simple Present, + Will
If I see Sam, I will ask him to give you a call.
OR
Will + If + Simple Present
You will always be able to take another test if you fail.
Note:
You can use these modal verbs instead of will: shall, can, may.
If you finish everything on time, you may go home earlier.
I can help you in your homework, if you ask me.
We shall meet on Sunday, if it's alright with you.

5. We use the second conditional when talking about future events that are not likely to happen.
"If I met a genie, I would ask for infinite wealth..."
Structure:
If + Simple Past, + Would + Base Form
If I met a genie, I would ask for money.
OR
Would + Base Form + If + Simple Past
I would be surprised if I saw money in my pocket.
We also use the second conditional when talking about things which are contrary to the present
facts.
If I had any money, I would give you some.
Note:
You can use these modal verbs instead of would: should, could, might.
If they wanted to move, they could sell the house to us.

6. The short form of would is 'd.
If Kathleen were at home, she'd pick up the phone.
Usually we say: I was, he was, she was, it was, we were, you were, they
were.
However, in these cases, we use:
I were, he were, she were, it were, we were, you were, they were.
In other words: "were" is the only form.
“If I were a boy, I think I could understand.”

7. We use the third conditional when talking about things which are contrary to the past facts. In
other words: events that did not happen in the past.
"If I had paid more attention, I wouldn't have hit myself..."
Structure:
If + Past Perfect, + Would have + Verb past participle
If I had told Sarah the truth, I would have felt much better.
OR
Would have + Verb past participle + If + Past Perfect
Tom would have helped us if he had known we were there.
Note:
You can use these modal verbs instead of would have: should have, could have, might have.
You could have arrived on time if you had used a map.