This document summarizes different types of conditional sentences in English: 1) First conditional - uses "if" with the present tense to talk about possible or probable future events. 2) Second conditional - uses "if" with the past tense to talk about improbable or hypothetical future events. 3) Third conditional - uses "if" with the past perfect tense to talk about improbable past events. It also discusses alternatives to "if" clauses and the use of "wish" to express regrets about present, past or hypothetical situations.