人教版八年级英语下册《Could you please clean your room?》SectionA PPT教学课件(第3课时)，共35页。
Objectives
To learn to make polite requests and ask permission politely.
To develop your summarizing skills.
To learn new words: pass, borrow, lend, finger, hate, while…
Warming-up
A: Mum, could I go out for dinner with my friends?
B: Sure, that should be OK.
A: Could I get something to drink with my friends after the movie?
B: Sure, you can.
A: Could I get something to drink with my friends after the movie?
B: No, you can’t, you have a basketball game tomorrow.
Grammar Focus
Could I go out for dinner with my friends?
Sure, that should be OK.
Could we get something to drink after the movie?
No, you can’t, you have a basketball game tomorrow.
Could you please take the dog for a walk?
OK, but I want to watch one show first.
Could you please take out the rubbish?
Yes, sure.
情态动词的语法特征
情态动词不能单独做谓语, 除ought和have外, 后面只能接不带to的不定式。
情态动词没有人称, 数的变化, 但有些情态动词, 如can、will也有一般式和过去式的变化。
情态动词的“时态”形式并不是时间区别的主要标志, 不少情况下, 情态动词的现在式形式和过去式形式都可用来表示现在时间、过去时间和将来时间。
can 和could：
1) can的主要用法：
A. 表示体力或脑力的能力：
e.g. The girl can dance very well.
B. 表示说话的推测﹑事物的可能性等:
e.g. Can the news be true?
C. 在口语中, can可以表示请求或允许:
e.g. Can I sit here?
can表示“能够”时与短语be able to同义，但can只用于一般现在时或过去时，而后者可用于各种时态。另外，can表示个人有某种能力，而be able to表示某人通过努力、克服困难做成某事，相当于succeed in doing sth.；叙述过去事实时，最好用was / were able to，因为could只表示过去具有某种能力。
2) could的主要用法：
A. could 是can的过去式, 表示与过去有关的能力和推测:
e.g. We all knew that the young man couldn’t be a doctor.
B. could可以代替can表示请求, 但语气较can 客气、委婉:
e.g. Could you lend me your dictionary?
Could I use your bike?
3) can和could接动词的完成形式，表示可能已经做某事。can用在否定和疑问句中，表示不相信、怀疑等态度。
e.g. They can’t have gone out because the light is still on.
以could或would提问时，不能再以could或would作答，而应该用can或will。如：
—Could I borrow your dictionary?
—Yes, of course you can.
could与can的区别
could与can都是情态动词，could是can的过去式。二者都可用于表示请求，但是用法稍有不同。
can 表示一般性的请求，语气随便，常用于熟人之间或长辈对晚辈，上级对下级的场合。
e.g. Can you tell us your story,Tony？
托尼，你能给我们讲讲你的故事吗？
could表示有礼貌的请求，语气委婉，常用于非熟人之间或晚辈对长辈，下级对上级的场合。比如：
— Could you tell us if it snows in winter in Australia?
— Sure.
— 请告诉我们，澳大利亚冬天下雪吗?
— 当然可以。
have to和must
1. 两词都是“必须”的意思，have to 表示客观的需要，must 表示说话人主观上的看法，即主观的必要。
My brother was very ill, so I had to call the doctor in the middle of the night.我弟弟病得很厉害，我只得半夜里把医生请来。(客观需做此事)
He said that they must work hard. 他说他们必须努力工作。(主观上要做这件事)
2. have to 有人称、数、时态的变化，而must只有一种形式。但must 可用于间接引语中表示过去的必要或义务。
He had to look after his sister yesterday.
3. 在否定结构中: don’t have to 表示 “不必”，mustn’t 表示“禁止”。
You don’t have to tell him about it.
你不一定要把此事告诉他。
You mustn’t tell him about it.
你一定不要把这件事告诉他。
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