人教版八年級英語下冊《Could you please clean your room?》SectionA PPT教學課件(第3課時)，共35頁。
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.
情態(tài)動詞的語法特征
情態(tài)動詞不能單獨做謂語, 除ought和have外, 后面只能接不帶to的不定式。
情態(tài)動詞沒有人稱, 數(shù)的變化, 但有些情態(tài)動詞, 如can、will也有一般式和過去式的變化。
情態(tài)動詞的“時態(tài)”形式并不是時間區(qū)別的主要標志, 不少情況下, 情態(tài)動詞的現(xiàn)在式形式和過去式形式都可用來表示現(xiàn)在時間、過去時間和將來時間。
can 和could：
1) can的主要用法：
A. 表示體力或腦力的能力：
e.g. The girl can dance very well.
B. 表示說話的推測﹑事物的可能性等:
e.g. Can the news be true?
C. 在口語中, can可以表示請求或允許:
e.g. Can I sit here?
can表示“能夠”時與短語be able to同義，但can只用于一般現(xiàn)在時或過去時，而后者可用于各種時態(tài)。另外，can表示個人有某種能力，而be able to表示某人通過努力、克服困難做成某事，相當于succeed in doing sth.；敘述過去事實時，最好用was / were able to，因為could只表示過去具有某種能力。
2) could的主要用法：
A. could 是can的過去式, 表示與過去有關的能力和推測:
e.g. We all knew that the young man couldn’t be a doctor.
B. could可以代替can表示請求, 但語氣較can 客氣、委婉:
e.g. Could you lend me your dictionary?
Could I use your bike?
3) can和could接動詞的完成形式，表示可能已經(jīng)做某事。can用在否定和疑問句中，表示不相信、懷疑等態(tài)度。
e.g. They can’t have gone out because the light is still on.
以could或would提問時，不能再以could或would作答，而應該用can或will。如：
—Could I borrow your dictionary?
—Yes, of course you can.
could與can的區(qū)別
could與can都是情態(tài)動詞，could是can的過去式。二者都可用于表示請求，但是用法稍有不同。
can 表示一般性的請求，語氣隨便，常用于熟人之間或長輩對晚輩，上級對下級的場合。
e.g. Can you tell us your story,Tony？
托尼，你能給我們講講你的故事嗎？
could表示有禮貌的請求，語氣委婉，常用于非熟人之間或晚輩對長輩，下級對上級的場合。比如：
— Could you tell us if it snows in winter in Australia?
— Sure.
— 請告訴我們，澳大利亞冬天下雪嗎?
— 當然可以。
have to和must
1. 兩詞都是“必須”的意思，have to 表示客觀的需要，must 表示說話人主觀上的看法，即主觀的必要。
My brother was very ill, so I had to call the doctor in the middle of the night.我弟弟病得很厲害，我只得半夜里把醫(yī)生請來。(客觀需做此事)
He said that they must work hard. 他說他們必須努力工作。(主觀上要做這件事)
2. have to 有人稱、數(shù)、時態(tài)的變化，而must只有一種形式。但must 可用于間接引語中表示過去的必要或義務。
He had to look after his sister yesterday.
3. 在否定結構中: 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訴他。
You mustn’t tell him about it.
你一定不要把這件事告訴他。
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