1、语法引导条件状语从句最常用的连词是if,由if引导的条件状语从句表示在某种条件下某事很可能发生。如:
If you ask him,he will help you.
如果你请他帮忙,他会帮你的。
If you fail in the exam,you will let him down.
如果你考试不及格,你会让他失望的。
if引导的条件状语从句既可以将从句放前面也可以将从句放后面
(如果天下雨,我们就不玩了)If it rains,we will stop playing.
转为We will stop playing if it rains.
2、另外,if从句还表示不可实现的条件或根本不可能存在的条件,也就是一种虚拟的条件或假设,从句多用一般过去时或过去完成时。
如:If I were you,I would invite him to the party.如果我是你,我会邀请他参加聚会。
I would have arrived much earlier if I had not been caught in the traffic.如果没有堵车,我会到的早一点儿。