First, Second and Third Conditional If

Conditional Clause and Main Clause

If I have enough money, conditional clause	I will go to Japan.     main clause
I will go to Japan, main clause	if I have enough money     conditional clause

First, Second, and Third Conditional

1. First conditional:	If I have enough money, I will go to Japan.
2. Second conditional:	If I had enough money, I would go to Japan.
3. Third conditional:	If I had had enough money, I would have gone to Japan.

Conditional clause	Main clause
1. If + Present Tense	will + inf / present tense / imperative
If you help me with the dishes (if + pres), I will help you with your homework. (will + inf) If the sum of the digits of a number is divisible by three, the number is divisible by three (Pres. tense) If you see Mr Fox tonight, tell him I am ill. (imperative).
2. If + Past Tense	would + inf
3. If + Past Perfect Tense	would have + past participle
We do not normally use will or would in the conditional clause, only in the main clause.

Uses of the Conditional

1. First conditional
   1. Nature: Open condition, what is said in the condition is possible.
   2. Time: This condition refers either to present or to future time.
      e.g. If he is late, we will have to go without him.
      If my mother knows about this, we are in serious trouble.
   
   
2. Second conditional
   1. Nature: unreal (impossible) or improbable situations.
   2. Time: present; the TENSE is past, but we are talking about the present, now.
      e.g. If I knew her name, I would tell you.
      If I were you, I would tell my father.
      Compare: If I become president, I will change the social security system. (Said by a presidential candidate)
      If I became president, I would change the social security system. (Said by a schoolboy: improbable)
      If we win this match, we are qualified for the semifinals.
      If I won a million pounds, I would stop teaching. (improbable)
   
   
3. Third conditional
   1. Nature: unreal
   2. Time: Past (so we are talking about a situation that was not so in the past.)
      e.g. If you had warned me, I would not have told your father about that party.(But you didn't, and I have).

Remember!

1. The conditional construction does not normally use will or would in if-clauses. EXCEPTION: If will or would express willingness, as in requests, they can be used in if-clauses.

e.g. If you will come this way, the manager will see you now.
I would be grateful if you would give me a little help.
(= ± please, come this way; please, give me...)

2. For the second conditional, were replaces was:

If I were a rich man...

3. After if, we can either use "some(-one, -where...)" or "any(-one, -where...).

If I have some spare time next weekend....or :
If I have any spare time...

4. Instead of if not, we can use unless.

e.g. I'll be back tomorrow unless there is a plane strike.
He'll accept the job unless the salary is too low.

5.There is a "mixed type" as well, for the present results of an unreal condition in the past:

If + Past Perfect - would + inf.
If you had warned me [then], I would not be in prison [now].

 Source: http://grammar.ccc.commnet.edu/grammar/conditional2.htm