This document discusses conditional sentences in English grammar. There are four main types of conditional sentences:
1) Zero conditional - Used to express general truths or facts. Both clauses use the simple present tense.
2) First conditional - Used to talk about possible or probable present or future events. The if-clause uses the present simple and the main clause uses the future simple or modal verbs.
3) Second conditional - Used to talk about unlikely or imaginary present/future situations. The if-clause uses the past simple and the main clause uses the conditional or modal verbs.
4) Third conditional - Used to talk about unlikely past situations. The if-clause uses the past perfect and the main clause uses