if 引导的条件状语从句------基本用法
一、定义：
If 意为“如果”，引导条件状语 从句，表示假如从句的动作发 生，主句的动作就(不)会发生。 If it doesn"t rain, I will go to the cinema tomorrow.
二、位置：
从句位置灵活，可放在主句之 前，但要用逗号与主句隔开；也 可放在主句之后。 My mother will take me to the park if she is free. If my mother is free, she will take me to the park
三：时态：
若主句为下列情形之一，条件状 语从句要用一般现在时
(1) 当主句为一般将来时：If he comes, he will bring his violin.
(2) 当主句的谓语中含有 can, may, must 等情态动词时：If you lose weight, you must eat less meat.
(3) 当主句为祈使句时：If you are not strong enough, please don"t take part in such an activity.
注：助记口诀 if 条件句不一般，三个要点记心间： 主将从现、主情从现、主祈从现。
If 引导的条件状语从句------句型转换
1. 借助“祈使句+and/or+句 子”来转换 (and 表顺承，or 表转折)
If you study hard, you will pass the exam easily. = Study hard, and you will pass the exam easily. = Study hard, or you won’t pass the exam.
2. 借助without或with来转换
If there is no water, fish will die. = Fish will die without water.
if 引导的条件状语从句------辨析
1. if 引导条件状语从句和宾语从句的区别
(1) if 引导条件状语从句，表示“如 果”，从句需要遵循主将从现的原则
If it doesn"t rain, I will go to the cinema tomorrow.
(2) if 引导宾语从句，表示“是否”， 从句不必遵循主将从现的原则
I don"t know if he will come tomorrow.
2. If 与其他常见连接词的辨析
(1) if 意为“如果” Difficulties are nothing if we are not afraid of them.
(2) unless 意为“除非；如果不” We’ll go there tomorrow unless it rains.
(3) until/ till 意为“直到…” not…until 意为“直到…才” We waited until he came back. She didn’t stop working until eleven o’ clock.
(4) although/ though 意为“尽管； 虽然” We were not tired though /although we had worked all day.
(5) since 意为“自从”或“既然” Great changes have taken place in China since 1978. Since everyone is here, let’s begin our meeting.
