There are four types of conditional sentences:
- Zero Conditional Sentences
i) refer to general truths such as scientific or natural facts;
ii) in this type of condition sentences, the time is now or always and the situation is real or possible;
iii) if-clause (Simple present) + Main clause (Simple present);
iv) use a comma after the if-clause when the if-clause comes before the main clause;
v) in zero conditional sentences, if the word ‘if’ is replaced by ‘when’, the meaning usually remains the same: When you heat up milk, the water starts to evaporate.
If you turn it upside down, the water rushes out.
If you stay up late, you’ll feel tired next day.
If you will stay up late, you’ll feel tired next day. ✗ (Don’t use future verb in the if-clause; also, when the sentence begins with when, both if-clause and main clause should be in simple present):
When you will heat up milk, the water will slowly evaporate. ✗
When you heat up milk, the water slowly evaporates. √
2. First Conditional Sentences
i) used to express situations in which a possible condition causes a possible result, though, not guaranteed;
ii) in this type of conditional sentences, the construction is based on ‘if this thing happens, that thing will happen’;
iii) the if-clause (Simple present) + Main clause (Simple future);
iv) use a comma after the if-clause when the if-clause precedes or succeeds the main clause.
If you start early, you’ll be home before dawn.
If anybody calls, tell them I’ll be back in two hours.
You’ll share my umbrella, if it rains.
If you carpool the children to school, you’ll save enough money.
Mother will be furious, if she finds out the truth about your grades.
If she doesn’t take the plunge, she’ll never marry to Bob.
Note that there are always some exceptions and special cases when we use conditional sentences.
We use the simple future in the If-clause when the action in the if-clause happens after the action in the main clause:
If you will send me the revised quotes, I’ll start working on this project immediately. (a request)
If it will make her happy, Bob will gift her with a car on her birthday.
3. Second Conditional Sentences
i) refer to unreal conditionals; not likely to happen in the future, not based on fact; a hypothetical condition and its probable result;
ii) used to express situations in which a possible condition causes a possible result, though, not guaranteed;
iii) in this type of conditional sentences, the construction is based on ‘if this thing happened, that thing would happen.’ (but not sure if the thing will happen) or that thing would happen;
iv) the if-clause (Simple past or continuous) + Main clause (an auxiliary modal verb i.e. would, could, should, might denoting an unlikely or unrealistic outcome):
If she was here, she would accompany us to the movies.
If you were driving from New York to Boston, which way would you prefer to go?
If it rained, she wouldn’t be able to attend the meeting.
I’d drop the children to school, if I had my car.
You got yourself into a mess if you told a lie.
In the second conditional sentences, when we express the unlikelihood of the situation; unlikely to happen, we use a modal auxiliary verb in the main clause:
If I knew how to swim, I’d cross the English Channel.
If my grandmother was/ were still alive, she would have all her teeth intact.
If I spoke Arabic, the multi-millionaire sheikh would hire me.
If she inherited her late husband’s fortunes, she would do a lot of philanthropic works.
Now notice the following examples, the first one has an error in the if-clause, should be in the past.
If they have their own children, they would be comfortably off. ✗
If they had their own children, they would be comfortably off. √
4. Third Conditional Sentences
i) refer to an unreal past condition accompanied by its probable result in the past expressing that present situation would be different if something different had happened in the past;
ii) in third conditional sentences, the if-clause is in past perfect (had + past participle) + Main clause (the modal auxiliary would, could, should, etc. + have + past participle); they express the theoretical situation that could have happened:
If doctor had operated on him in time, his life would have been saved.
If she had told him she didn’t like him, he would have gone for Jane because she values him as a person.
If the UN had not rushed medical aid and food to the earthquake sites, there would have been far too many deaths.
If you had told me you needed to stay at my apartment, I would have left the keys with the neighbour.
If he had behaved himself in the prison, he could have been let out on probation.
If Jack had done the assignments, he could have gone out to play.
Notice that in all these sentences, the subject of the statements was capable of doing something, but they did not. All these situations are likely, but did not happen.
Now, note the following common errors in the third conditional sentences:
If Barbara would have lent me money, I would have finally succeeded in the property world. ✗
If Barbara had lent me money, I would have finally succeeded in the property world. √
(In third conditional sentences, do not use a modal auxiliary verb in the if-clause).
Inversion in Conditional Sentences
In formal or literary English, we also inverse the if-clause:
Had the doctor not done caesarean section, the newborn would have died. (= If the doctor had not done caesarean section….)
It would be humiliating, were he to be told he was a complete idiot. (= If he were to be told he was a complete idiot….; the likely or unlikely result is particularly awful or unthinkable; used to express hypothetical scenarios in the present, future, and past).
Should you need extra beddings, just call the manager. (= If you should need extra beddings….)
When one situation is dependent on another situation or on a person, we use ‘if it was/ were not for.’
If it wasn’t/ weren’t for Mr. Wilson, I wouldn’t be selected for the national team.
Were it not for Mr. Wilson, I wouldn’t be selected for the national team. (formal, literary)
When we talk about the past, we use ‘if it had not been for’ + noun:
If it hadn’t been for Mr. Wilson, I wouldn’t have been selected for the national team.
Had it not been for Mr. Wilson, I wouldn’t have been selected for the national team. (formal, literary)