There are four types of conditional sentences ： Real present: Water boils if it is heated to 100 degrees celcius. Real future: If it rains tomorrow, we will take our umbrellas . Unreal present / future: If I called the president , he probably wouldn't’t speak to

me . Unreal past: If she hadn’t been dancing, she would never have broken her leg. 

Real conditionals are used when the if clause expresses an idea that is probably true , or at least very possible .

A real present condition is one in which the situation is true in the habitual present time . This form is usually used to express general truths .

If it rains , we swim at the gym .

Water boils if it is heated to 212 degrees Fahrenheit .

In examples , the simple present is used , but depending on the intended meaning , we could also see the present progressive , a present modal , or even the present perfect , as the following examples illustrate.

If it is raining , we may swim at the gym .

Water boils if it has been heated to 212 degrees Fahrenheit .

A real future condition is one in which the situation will most probably be true in the future .

If it rains tomorrow, we will carry our umbrellas .

Imperative verb forms are also possible in the result clause .

Tell me if you see anything strange.

Real future conditions can also be formed with the modal should . This conveys the impression that the action in the if clause is a little less likely ( though still far more likely than it would be if the unreal present or future were used ). It is also fairly formal .

If I see her , I will tell her . ( It is likely that I will see her . )

If I should see her , I will tell her. (It is a little less likely that I will see her . )

Note that the modal will is almost never used in an if clause .

We use unreal conditions when the idea expressed in the if clause is impossible or unlikely .

The unreal / future condition is one in which the action is impossible or highly doubtful in the opinion of the speaker .

If I called the president , he probably wouldn't’t speak to me .

If the United States won the next World Cup Games , the entire world be shocked .

The time reference in this type if conditional is either to a repeated, habitual event or to a specific point in the future :

If I called the resident, he probably wouldn't’t speak to me. Note that the verb in the if clause is identical in form of past and the verb form in the result clause begins with the modal would plus the simple form of the main verb. In reality, either the simple past or the past progressive could be used in the if clause. And would, could, or might could be used in the result clause.

If + simple past/past progressive,subject+would/might/could+simple word form of the verb

If the United States won the next World Cup Games,the entire world would be shocked.

If they were playing instead of sleeping ,their mother might be very angry.

A past tense verb in an If clause refers to the unreal present and not the past.

Progressive forms are possible in the result clause:If their mother were working ,the children would probably be playing.

Unreal Past Conditional SentencesAn unreal past conditional is one in which the situation did not occur in the past .In such sentence, the speaker is imagining the past as different form way it happened. The speaker is talking about “the way things could have been” under a different set of condition.

If there had been more time, we would have finished the project.

Lisa would never have seen South America if she hadn’t met that young man from Bolivia. 

In the unreal past, the verb in the if clause is identical in form to the past perfect(or past perfect progressive) and the verb in the result clause contains the modal would, might, or could plus the perfect auxiliary have plus the past participle of the main verb.

If +past perfect or past perfect progressive, subject+would/might/could+HAVE+past participle If she hadn’t been dancing, she would never have broken her leg. If we had seen you at the party, we might have stayed longer. Like the unreal present, the result clause may contain a progressive form:If I had taken that job that paid so little, I would have been watching every penny I spent.

• What are they?: Combination of two different conditional structures.

• When do we use them?: When the two parts of a conditional sentence refer to different times.

The most common combinations are:

• Past Condition / Present Result

• The first one has a condition in the past and a present result. We use it to express that if something had been different in the past there would be a present result.

• For example: if we hadn't missed our flight we'd be in Spain now.

• The structure is: If + past perfect, would (could, might) + infinitive.

• Present Condition / Past Result• The next one has a present condition and a past

result. We use it to express that due to certain present conditions something already happened in the past.

• For example: if I was more diligent, I would've finished my degree at university. The meaning is: I am not a diligent person and because of this present condition I have never finished my degree.

• The structure is: if + past simple, would (could, might) have + past participle.

EXERCISES

Complete sentences with the appropriate conditional form:

1. It’ll be quicker if we …….. a taxi to the airport. (get)

2. If the company stopped advertising online it ……. (have) higher operating costs.

3. I think he’d be happier if he …..(not live) alone.

4. The managing director wouldn’t have fired so many of his employees if they …….. (relocate) earlier.

5. We don’t start if all the students ……..(talk)

6. I’ll be very surprised if Maria ….(not get) the job that was advertised here last week.

7. If you cross an international date line, the time…..(change).

8. If the entrepreneur hadn’t taken so many risks, the company ……….(not close down).

9. All the goods would have sold out If we ……….. (drop) the prices a little.

10. If I ……… (pass) all my exams I would be working by now.

11. If I ………(to be) you, I’d leave it until tomorrow.

KEY 1. It’ll be quicker if we get a taxi to the airport. 2. If the company stopped advertising online, it would have higher

operating costs.3. I think he’d be happier, if he didn’t live alone.4. The managing director wouldn’t have fired many of his employees if

they had relocated earlier.5. We don’t start if all the students are talking.6. I’ll be very surprised if Maria doesn’t get the job that was advertised here

last week.7. If you cross an international date line, the time changes.8. If the entrepreneur hadn’t taken so many risks, the company wouldn’t

have closed down.9. All the goods would have sold out, If we had dropped the prices a little.10. If I had passed all my exams, I would be working by now. (mixed cond)11. If I were you, I’d leave it until tomorrow.