be able的所有其他时态,都按照普通动词的规则来构成:
现在完成时:have been able
过去完成时:had been able
否定疑问式:could you not?/couldn't you?were you not?/weren't youable?will you not?/won't you be able?等
can/be/will/shall not和 have都可以按通常方法缩略:
I wasn't able he won’t be able I've been able
can后面带不带to的不定式(即动词原形)。
be able后面带有 to的不定式。
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[Amber demo]
137 can/am able,could/was able
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A can与 be able
1 shall/will be able是唯一的将来时形式:
Our baby will be able to walk in a few weeks.
我们的宝宝再过几个星期就能走路了。
2 can和be able都可用于现在时,can则更常用些:
Can you/Are you able to type?
你会打字吗?
I can't pay you today.Can you wait till tomorrow?
今天我不能付你钱。你可以等到明天吗?
Could you wait?
您能等候吗?(参见下面B2。)
3 在现在完成时中,必须用be able形式:
Since his accident he hasn’t been able to leave the house.
自从他遇到意外以后,他一直没能出门。
B could
1 如存在着条件的含义,could可以用来表示现在时的意义:
Could you run the business by yourself?
你能自己管理这企业吗?(如果必要的话)
Could he get another job?
他能找到另一份工作吗?(如果他辞掉这份工作的话)
I could get you a copy.
我可以给你弄到一本。(如果你想要的话)
在头两个例句中could可以用would be able替代。
2 could you?是一种极好的表示请求的方式。它跟 would you?
可以替换使用,但比后者更有礼貌些:
Could you show me the way/lend me£5/wait half an hour?
你能给我指一下路/借我五英镑/等半小时吗?
Could you please send me an application form?
您能否寄给我一份申请表?
couldn't you?也是很有用的:
Householder:Could you come and mend a leak in a pipe?
房主:你能不能来修理一下管道?
Plumber:Would sometime next month suit you?
管道工:您看下个月什么时候合适吗?
Householder:Couldn't you come a little earlier?
房主:你是否能提前一些日子来?
C could和was/were able用于表示过去的能力
1 只表示一般的能力时,两者都可用:
When I was young I could/was able to climb any tree in the forest.
我年轻的时候,林子里的什么树我都能爬。
2 表示能力+特定行为时,要用 was/were able:
Although the pilot was badly hurt he was able to explain what had hap- pened.
飞行员的伤势虽然很重,但是他还能够解释发生的一切。(他能够而且的确作了解释。)
The boat capsized quite near the bank so the children were able to swim to safety.
船是在离岸很近处翻的,因此,那些孩子能够游到安全的地方。(他们能够也的确游到安全的地方。)
但是,这一规则用于否定句中表示未能发生的事时或与表示感觉的动词连用时,就不那么严格了:
He read the message but he couldn't/wasn't able to understand it.
他读了那张纸条,但却不懂是什么意思。
I could/was able to see him through the window.
我透过窗户能看见他。
D 过去完成式是 had been able:
He said he had lost his passport and hadn't been able to leave the country.
他说他丢了护照因而不能离开这个国家。(有关could在间接引语中的用法,参见第312节。)
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[Amber demo]
138 could+完成式
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A 这种结构表示过去的能力,表示动作并未付诸实施:
I could have lent you the money.Why didn't you ask me?
我那时是能借钱给你的。你为什么没有向我借?
(另参见第154节。)
或用于表示不知道行动是否已付诸实施的场合:
The money has disappeared!Who could have taken it?
钱不见了!谁会把它拿走呢?
Tom could have(taken it);he was here alone yesterday.
有可能是汤姆把它拿走的;昨天他单独一个人在这里呆过。
比较以下两句:
He was able to sent a message.
他设法送了个信来。(他送了。)
He could have sent a message.
他本可以送个信来。(他没有送,或者我们不知道他是否送过。)(另参见第135节。)
B could+完成式可表示因别人没做某事感到不满或责备:
You could have told me.
你本来可以告诉我的。相当于:
I am annoyed/disappointed that you didn't tell me.You should have told me.
你没告诉我,我感到不高兴/失望。你本来应该告诉我的。
说话的人要对自己希望强调的词重读。
(关于might的同样用法,参见第285节。)
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[Amber demo]
第十四章ought,should,must,have
to,need表示义务?
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[Amber demo]
139 ought的各种形式
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ought是情态动词。(参见第107节B。)
ought没有其他形式,可用于现在时以及将来时。用于过去时则位于动词过去式之后或不定式的完成式之前:
I ought to write to him today/tomorrow.
我今天/明天应该给他写封信。
I knew I ought to write to him.
我那时知道我应该给他写封信。
She said I ought to write.
她说我应该写。
I know/knew that I ought to have written.
我知道/那时知道我该写的。
否定式:ought not/oughtn't
疑问式:ought I?等
否定疑问式:ought I not?/oughtn't I?等
ought与带to的不定式连用。为了提醒学生这一点,常称之为ought to。
问句或话语中用ought to的时候,可以用 should来回答;用should的问句或话语也可以用ought to回答:
—You ought to put in central heating.
—Yes,I suppose I should.
—你应该装上暖气。