Conditional sentences are one type of complex sentences in which we have a dependent and an independent clause. The dependent clause is known as if-clause and the independent clause is called main clause. It is more common to put the if-clause first. So the total structure for conditional sentences would be as follow:
If dependent clause,independent clause.
Conditional sentences are divided into four types,three of which are the most common:
TypeI:
The formula for this type of conditional sentence is as follow:
If simple present,simple future with will. This conditional sentence is real. That is the situation described by the clauses can happen. In order to show possibility , we can use to be going to,may,or might in the main clause. Sometimes we use will in both of the two clauses which has the meaning of "be willing to". We may also use the modal should in the if-clause which has the meaning of "if it happens'". So other forms would be as follow:
If simple future with will,simple future with will.
If simple present with modal should,simple future with will.
We can also use imperative sentences in conditional sentences typeI, but we can not use it in other types of conditional sentences.
Conditional sentences type II:
In those conditional sentences , we use a simple past tense in the if-clause and the modals: would,could,and might in the main clause so the formula for this type of conditional sentence is as follow:
If simple past,a past tense containing modals could ,would , or might.
This type of conditional sentences have unreal meanings about present. It means by saying those sentences we mean the opposite thing in present. Here are some examples:
If I had two cars , I could give one of them to you. This sentence means:" I don't have two cars , so I can't give one of them to you."
If I were a bird , I could fly. This sentence means:" I am not a bird, so I can't fly."
Because conditional tenses type II are unreal , we use were instead of was for I , he , she , and it.
Conditional Sentences type III:
In those conditional sentences , we use a past perfect tense in the if-clause and would have , could have , or should have in the main clause. Those conditional sentences are unreal about the past time.
If I had gone to school , I could have learned a lot.
The above sentence means: '' I did not go to school , so I did not learn anything.
Sometimes we use a simple present tense in both if-clause and the main clause. In this case the conditional sentence reveals a permament fact which is always true. If can be replaced by whenever in this type of conditional sentence.
If simple present , simple present.
If I watch Tv , I eat something. It means : Whenever I watch Tv , I eat something.
It is also possible to use a simple past tense in both the if-clause and the main clause. In this case , the conditional sentence expresses something which was always true in the past.
If simple past, simple past.
If I drank water , I felt good. It means : Whenever I drank water , I felt good.