This document discusses different types of conditional sentences in English grammar. It begins by providing examples of four conditional sentences with different structures. It then explains the three main types of conditional sentences: 1) Zero conditional sentences describe general truths using the present simple tense in both clauses. 2) First conditional sentences describe possible events in the present or future using the present simple in the if-clause and future simple or modal verbs in the main clause. 3) Second conditional sentences describe unlikely or imaginary situations using the past simple in the if-clause and modal verbs or "would" in the main clause. The document concludes by providing another example of a third conditional sentence using "would have + past participle"