Conditionals have two parts: a main clause and an if clause. There are three types of conditionals: 1) real possibility conditionals use present tense in the if clause and future tense in the main clause, 2) unreal conditionals use past tense in the if clause and conditional tense in the main clause, and 3) past conditionals use past perfect tense in the if clause and conditional perfect tense in the main clause.

1. CONDITIONAL
CLAUSES

2. Conditionals
always have two parts:
the Main Clause
and
the IF Clause
(When the If Clause goes first, it is followed by a
comma, but you can also put the Main Clause
first without using a comma between the
clauses.)

3. Conditional Conjunctions:
IF is the most common one.
Others are:
As long as
Provided/ Providing (that)
UNLESS = If not

4. 1st Type Conditional
(Real Possibility)
It is used for real - or possible - situations.
The If Clause goes in the Present
Tense (usually Simple):
If you want , …
If you are late again, …
If you have done your homework, …

5. The Main Clause can go in:
- Present Tense
- Imperative
- Present Modal Verb: can, may, must.
But usually in
- FUTURE SIMPLE:
-If you want, I’ll help you
-I ’ll be angry if you’re late again
-If you’ve done your homework,
you can go out

6. UNLESS is the opposite of “If”:
If she doesn’t call soon, I’ll be angry =
Unless she calls soon, I’ll be angry.
He will be late if he doesn’t hurry up =
He will be late unless he hurries up

7. 2nd Type Conditional
Often called the "unreal" conditional
because it is used for unreal -
impossible or improbable - situations.
This conditional provides an
imaginary result for a given
situation.

8. The If Clause goes in
Simple Past Tense
The verb 'to be', when used in the 2nd conditional,
is usually conjugated as 'were'.
The Main Clause goes in
Conditional Tense:
Would(n’t) + infinitive
(Could or Might are also possible but less common)
If I were you, I’d go to the doctor’s.
If he studied more, he’d pass all his subjects.
They would buy a new house if they had more money.

9. 3rd Type Conditional
Known as the "past" conditional
because it refers only to past
situations with hypothetical
results.

10. The If Clause goes in
- Past Perfect
The Main Clause takes:
WOULD(N’T) (Could/ Might) HAVE +
Past Participle
He would have found a new job if he had tried.
We wouldn’t have seen this film if you hadn’t told me about it.
If you had studied for the exam, you would have passed.

11. To sum up:
(Taken from
http://www.xtec.es/~ogodoy/sac/rephrasing/conditionals.htm)