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译林版（2024）八年级上册英语 Unit4 单元语法知识点 讲义
祈使句
当我们向他人发出命令、提出要求或建议时,常使用祈使句。如:
Be quiet, please! 请保持安静！
Don't be late again! 不要再迟到了！
注意:祈使句的主语通常不明确表示出来。
祈使句的肯定形式以动词原形开头,其否定形式通常是在动词原形前加do not/don't。
为了显得更为客气和礼貌,我们常在祈使句中加上please。当please用在句末时, 常用逗号与其余部分隔开。如:
Please pass me the ball. 请把球传给我。
Open the window, please.请把窗户打开。
句型“Let’s ...”表示说话人向对方提出建议。如:
Let's visit Nanjing Museum first! 让我们先参观南京博物院吧！
归纳总结：
一、祈使句的肯定形式：
1. Be型: 以系动词be开头的祈使句。如：Be patient! Be a good student!
Be careful when you use it.
2. Do型: 以实义动词开头的祈使句。如：
Read them slowly and carefully! Please hand the tools to me.
3. Let型: 以实义动词let开头的祈使句。如：
Let him do it by himself. Let's put the pieces of wood together.
二、祈使句的否定形式：【一般在动词上否定，也可以用否定副词（never）来表示】。
1. Don’t be +其他成分（形容词、名词或介词短语）。如：
Don’t be afraid. Never be late again next time!
注意：在这种句型中，be不能省略；否定副词not不可置于be之后。
2. Don’t +动词原形+其他。如：
Don't mix them up! Please don’t give up! Never do it again!
3. Let引起的祈使句有两种否定形式:
1). Let+宾语+not+动词原形+其他。如：Let her not do that. Let’s not think about it.
2). Don’t+ let+宾语+动词原形+其他。如：Don’t let Jim do that. Don’t let us go, please.
4. 在公共场合的提示语中，否定祈使句常用“No＋名词 / V-ing形式”结构，表示“禁止做某事”。如： NO PHOTOS! 禁止拍照！ No parking! 禁止停车！
注意：
1). 在表达请求或劝告时，有时为了表示委婉的语气，可以在句首或句末加please，但是如果please加在句末，应用逗号将其与前面的部分隔开。 如：Sit down, please. Please look after the twins.
2). 在意思比较明显的情况下，可以把谓语动词省略。如： This way, please.
3). 有时为了加强语气，可以在动词前使用do. 如：Do be careful！一定要小心！
4). 有时为了强调对方，也可加上主语you，人名或everybody, anybody等不定代词。如：You sweep the floor and I clean the window. Stand up, everybody.
5). 有时为了明确向谁提出请求或发出命令，可加称呼语，但称呼语要与句子用逗号隔开。 如：Put the shirt on the bed, Jim.
拓展：
祈使句的反意疑问句:
1.祈使句的反意疑问部分为肯定形式，要用shall，will。如：
Pass me the book，will you
2. Let’s表示第一人称的祈使句，反意疑问句为“Shall we ”。如：
Let’s go for a walk，shall we // Let’s forget it，shall we
3. Let me和Let us 表示第二人称的祈使句，反意疑问句为“will you ”。如：
Let us go for a walk，will you
4.其它行为动词引起的祈使句，无论其陈述部分是否定还是肯定的祈使句，多用“will
you ”，表一种客气的语气。如：
Listen to me，will you // Don’t tell anyone about it，will you
但在肯定的祈使句后有时也用“won’t you ”表“提醒对方注意”或表“邀请”。如：
Have a cup of coffee，won’t you
Come in and take a seat，won’t you／will you
巩固练习------句型转换。
1.We had to be careful not to hurt ourselves.(改为祈使句)
_______ _________ __________ ___________ hurt ourselves, please.
2. Don't mix them up! (改为肯定句)
__________ ___________ __________, please.
3. Look at the picture. (改为否定句)　
______ ______ _______ the picture.
4. If you don't listen to me, I'll go. (改为同义句)
________ _________ me, or I'll go.
5.Speak slowly and clearly, ______________ (改为反意疑问句)
答案：
1.Be careful not to;
2. Mix them up
3.Don’t look at;
4. Listen to;
5. won’t you／will you
用should和 had better提建议
情态动词是一种本身有一定的词义,表示说话人的情绪、态度或语气的动词,但不能单独作谓语, 只能和其他动词原形构成谓语;没有人称和数的变化。当我们给他人提建议时,可以用should 和had better, 表示“应该”或“最好”做某事, had better语气比should 强一些。如:
You had better water the flowers as soon as possible.你最好尽快给花浇水。
All of us should take part in this activity. 我们每个人都应该参加这项活动。
注意: should 和 had better都是情态动词,后接动词原形,而且均没有人称和数的变化。
had better 中的 had常缩略为'd。即had better= 'd better；如:
We'd better leave before it rains. 我们最好在下雨前离开。
should和had better的否定形式是:should not/shouldn't和 had better not。如:
He shouldn't be late for school again.他不该再迟到了。
You had better not play the piano now.现在你最好别弹钢琴。
拓展：
1. had better在反意疑问句中的运用：通常用had, 有时也可以用will you。如：
You'd better not go out today, had you 你今天最好不要外出，好吗？
I must stay at home this afternoon，you had better come to my house, will you 今天下午必须留在家里，你最好来我家，好吗？
2.should表推测: 用于肯定句，表示按常规、常理的推测，意为“按理应该”。如：
It’s nearly seven o’clock. Jack should be here at any moment.
I have bought three boxes. That should be enough.
3.Should…do… 疑问句中译为“本该------”（含有责备意味）。
Should I wear the uniforms every day Yes, you should. // No, you needn’t.
巩固练习：按照要求完成下列句子。
1. You'd better get too much paint on the brush. (改为否定句)
You _______ _______ ________ ________ too much paint on the brush.
2. You’d better not smoke any longer, ________ ________ (改为反义疑问句)
3. You shouldn't go too fast. (改为肯定句)
You _______ _______ ________ __________.
4. If you have a backache, you _____ lift heavy things. You _____ lie down for a good rest.
A. had better, shouldn't B. shouldn't; had better not
C. shouldn't; had better D. had better not; mustn't
5. -I have a stomachache. What should I do
-You_____ drink sweet water and _______eat sweet food.
A. had better not; shouldn't B. should; had better
C. had better; had better D. shouldn't; should
答案：
1.had better not get；
2.had you/will you；
3.should go too fast；
4. ( C )；
5. ( A )；

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