CONDITIONAL SENTENCES

Conditional Sentence Type 1

It is possible and also very likely that the condition will be fulfilled.

Form: if + Simple Present, will-Future

Example: 

Positive	Negative	Question
If I see him, I'll (I will) tell him.	If you don't hurry, you'll miss the bus.	What will you do if there is a problem?

Conditional Sentence Type 2

It is possible but very unlikely, that the condition will be fulfilled.

Form: if + Simple Past, Conditional I (= would + Infinitive)

Example:

Positive	Negative	Question
If I had more time, I'd (I would) travel more.	I wouldn't (would not) refuse if you offered me $10,000.	What would you say if you met Queen Elizabeth?
If I were you, I'd leave the job.	I wouldn't (would not) leave the job if I were you.	Would you leave the job if you were me?

Conditional Sentence Type 3

Form : if + Past Perfect, main clause with Conditional II

Conditional Sentences Type III refer to situations in the past. An action could have happened in the past if a certain condition had been fulfilled. Things were different then, however. We just imagine, what would have happened if the situation had been fulfilled.

Example:

Positive	Negative	question
If I'd (I had) known you were coming, I would have waited for you.	If she hadn't (had not) been ill, she would have gone to the cinema.	Would you have done it if you'd (you had) known earlier?

The main clause can also be at the beginning of the sentence. In this case, don't use a comma. Example: I would have sent her an invitation if I had found her address.

Note: Main clause and / or if clause might be negative. See Past Perfect and Conditional II on how to form negative sentences. Example: If I hadn’t studied, I wouldn’t have passed my exams.

Uses of the Conditional

1. First conditional

a.    Nature: Open condition, what is said in the condition is possible.

b.    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

a.    Nature: unreal (impossible) or improbable situations.

b.    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

a.    Nature: unreal

b.    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....f 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].

You should find out more about conditional sentences in this link http://www.englisch-hilfen.de/en/grammar/if.htm