Conditional Sentences are also known as Conditional Clauses or If Clauses. They are used to express that the action in the main clause (without if) can only take place if a certain condition (in the clause with if) is fulfilled. There are three types of Conditional Sentences.
Conditional Sentence Type 1
→ It is possible and also very likely that the condition will be fulfilled.
Example: If I find her address, I’ll send her an invitation.
Conditional Sentence Type 2
→ It is possible but very unlikely, that the condition will be fulfilled.
Example: If I found her address, I would send her an invitation.
Conditional Sentence Type 3
→ It is impossible that the condition will be fulfilled because it refers to the past.
Example: If I had found her address, I would have sent her an invitation.
Sometimes Conditional Sentences Type I, II and III can also be used with other tenses.