Question

if引导的条件状语从句

Answer 1

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.
一、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
二、结构
if+陈述句，主语+谓语或:主语+谓语+if+陈述句
紧跟着if的是从句
从前主后逗号隔开，主前从后if连接
三、用法
1.当主句为一般将来时，if引导的条件状语从句常用一般现在时。（主将从现）If it doesn't rain tomorrow,we will go to the zoo.如果明天不下雨，我们将去动物园。If you come to the party,you will have a great time.如果你来参加派对，你将玩得很开心。
2.当主句有情态动词can,may,must，need等时，从句常用一般现在时。（主情从现）He should see a doctor if he has a fever.如果他发烧了，他应该去看医生。She need go home at once,if she miss her son.如果她想念儿子，她需要马上回家。
3.当主句为祈使句时，从句常用一般现在时。（主祈从现）Please call me if he comes back.如果他回家请打电话给我。Don't forget to tell me if your finish your work.如果你完成了你的工作，不要忘记告诉我。
注意:
1.当主句为过去将来时，if从句用一般过去时态(若有be动词，用were),此时表达与事实相反的推测，用虚拟语气。If I were you,I would tell her.如果我是你，我会告诉他。If you helped me,I would be very thankful.如果你帮助了我，我会非常感激。
2.if 在宾语从句中表示“是否”，相当于whether.
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。
四、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.