Conditional Mood

There are four types of conditional mood which are as the following:

.Type one

The first conditional is used to express situations based on fact in thepresent or future (things which may happen).

(IF Clause)------------------(Main Clause)

If I see you tomorrow,........I will buy you a drink.

Note! We never use will, or won't in the if clause.
For example:
If I have time today, I will phone my friend. = I will phone my friend, if I have time today. (It is possible that I will have time - therefore the condition is real).
If I go to England, I will buy some Cheddar cheese. = I will buy some Cheddar cheese, if I go to England. (It is possible that I will go to England - therefore the condition is real).

. Type Two

The 2nd conditional is used to express unreal situations in the present or future. Often used to express a wish.
Uses the simple past tense

(IF Clause)--------------(Main Clause)

If I won the lottery,.......I would buy a new house.

Note! We never use would, or wouldn't in the if clause.
For example:
If I were you, I wouldn't do that. = I wouldn't do that, if I were you. (I am not you - therefore the condition is unreal).
If I had more time, I would do more on my websites. = I would do more on my websites, if I had more time. (I don't have more time - therefore the condition is unreal).

. Type Three

Used to express conditions in the past that did not happen. Often used to express criticism or regret with would have, could have or should have.
Uses the past perfect tense:-

(IF Clause)-------------------(Main Clause)

If I had worked harder.......I would have passed my exam.
If I had worked harder,......I could have passed my exam.

Note! We never use would have, or wouldn't have etc in the if clause.

For example:

• If I hadn't helped you, you would have failed. = You would have failed, if I hadn't helped you. (I helped you so you didn't fail).
  
• If it had been sunny, we could have gone out. = We could have gone out, if it had been. (We didn't go out because it wasn't sunny).

.Type Zero

The conditional 0 is used to express general truths and facts (often things based on scientific fact).
Uses the simple present tense

(IF Clause)..........................(Main Clause)

If you heat water to 100°C,,........ It boils

For example:
If you drop an apple, it falls. = An apple falls, if you drop it. (This is an absolute truth based on scientific fact - gravity).
If you don't do your homework, I will be disappointed. = I will be disappointed, if you don't do your homework. (This is a general truth based on previous knowledge - you know that I am disappointed if people don't do their homework).
Note! Most zero conditional sentences mean the same thing if "when" is used instead of "if".