Although most student grammars focus on four common patterns of conditional sentences or if-clauses which are often called zero, first, second and third conditionals, conditional sentences in English language have a variety of conditional forms and sentence structures.
Here are some of the most common uses of conditional sentences which will be discussed in detail later:
1. Uncertain events & situations
We use conditional sentences to talk about uncertain events and situations.
Example:
Ask Mark if he is staying tonight. (He may or may not be staying)
If I see Nicky, I will give convey your message. (I may or may not see Nicky)
2. Conditions
An if-clause can also refer to a condition – something which must happen first, so something else can happen.
Example:
If we can get there by tomorrow morning, we can have breakfast at Mark’s place.
I will go to market tomorrow if I am able to repair my car today.
3. If…then
We sometimes construct sentences with if…then to emphasize that one thing depends on another. But note that we do not use if…so in this way.
Example:
If he cannot walk, then she will have to help him. (NOT …so we will have to go and see her)
If Jennifer has no enough money, then we have to lend her some money.
4. If meaning “if it is true”
Another common use of if is to mean “if it is true that” or if it is the case that”
Example:
If you were in New York, why didn’t you come and see us?
If it will help you, I will lend you some money
5. Unlikely, imaginary or untrue situations
Past (or special) tenses can be used to give the idea that something is unlikely, imaginary or untrue.
Example:
If I married you, we would both be unhappy. (Past tense used to talk about an imaginary future situation).
Sumber : http://www.conditionalsentences.org/
