This document describes the three types of conditional sentences in English. First conditional sentences express real possibilities using "if" + present tense in the conditional clause and future tense in the result clause. Second conditional sentences refer to unlikely present or future events using "if" + past tense in the conditional clause and "would" in the result clause. Third conditional sentences refer to impossible past events using "if" + past perfect in the conditional clause and "would have" in the result clause.