Conditional sentences are used to express that the action in the main clause can only take place if a certain condition is fulfilled. Full conditional sentences contain two clauses: the condition, and the result.
There are two kinds of conditional sentences: real and unreal.
Real conditional: describes real-life situations. Real conditional can be further divided into two types.
1) Zero conditional: The “Zero” conditional is used to express general truth or things that are always true as long as the condition is fulfilled.
Formation: if + present simple + present simple
2) First conditional: The ‘First Conditional’ is used to express a theoretical condition that is possible and also almost certain that the condition will be fulfilled.
Formation: if + Simple present + Subject + will (future)/infinitive/modal + base verb
Unreal Conditional describes unreal, imaginary situations. There is no possibility or very little possibility for the conditions to be fulfilled. Unreal conditionals are of two types.
1) Second conditional: The second conditional is often used to express a wish. We wish for something to take place in the future. But it is almost impossible that the condition will be fulfilled in our lives.
This conditional is often used by ‘day dreamers’.
Formation: If + past simple + would +base verb
2) Third conditional: Third conditional is used when we are talking about the past and imagining something different from what had actually taken place. It is not possible to fulfill the condition which is given in the ‘if – clause’ because the situation has already happened in the past.
This conditional is often used to express criticism or regret.
i) If clause: If + subject+ past perfect verb
ii) Main clause: Subject + would/could/might+ have + past participle