could的否定形式是could not,多縮寫為couldn't,兩者通常都讀作[>kudnt].
（1）表示能力,意思是：能,會.
例
Could you speak English then?那時妳能講英語嗎?
He said he couldn't follow me.他說他跟不上我.
註意：①could（能）和was/were able to 都表示過去壹般具有某種能力.
例
He could (was able to) swim very well when he was nine.他九歲時就很會遊泳.
②was (were) able to 可以表示過去某時有某種具體的能力並且實際上可以做到,但could表示過去的習慣能力.
例
Although the driver was badly hurt,he was able to explain what had happened.司機雖受重傷,但仍能說明發生了什麽事.
（2）表示可能性,意思是：可能.
例
That big cinema can seats 2,000 people.那家大電影院能坐2,000人.
He said he couldn't come.他說他不能來.
（3）提出請求、疑問或看法（could是虛擬語氣,代替can,在時間上與can沒有區別,只是語氣比can委婉.can語氣直爽、肯定）.
例
----Could you let me have your passport?
----Yes,here it is.
—看看妳的護照好嗎?
—行,這就是.
（4）表示驚異、不信等情緒（用於疑問和否定句中,此時could與can用法相同,無時間上的差別,用could語氣緩和,情緒要弱）.
例
Who could have taken them?誰會把它們拿走了呢?
She couldn't have left so soon.她不可能這麽快就走了.
（5）表示與事實相反的情況（用於虛擬語氣）.
例
How I wish I could go with you!我多麽希望和妳們壹道去!
would的用法
1) 用於提出提議或邀請
例：Would you like to change a seat?It's warmer here.（您要不要換壹下座位?這裏暖和些.）
Would you prefer a hardback edition?（您要不要買壹本精裝本?）
2) 用於提出客氣的要求或請求：
例：I would like you to fetch that document for me now.（我想請妳現在就幫我把那份文件取來.）
I would like to know more about your plan.（我想更多地了解壹下妳的計劃.）
3) would you mind + doing句型通常用於表示請求對方做壹件有壹定麻煩的事情,語氣壹般都非常客氣.註意回答時通常是肯定的,以表示願意做所要求的事情.
例：Would you mind filling in this form?（請您填壹下這張表.）
Would you mind repeating what you just said?（請把剛才的話重復壹遍好嗎?）
4) 用於委婉地表示自己的意見：
例：I would think the journey will take something like two weeks.（依我看,這次旅程大約需要兩個星期.）
I would look at the problem a little differently.（我對這個問題的看法略有不同.）
5) 用於表示過去經常性的行為或動作：
例：The retired captain would sit hours on end watching ships sailing past.（退休的船長經常坐在海邊觀望過往的行船,壹坐就是幾個小時.）
He would go to bed strictly at 9,and on Sundays would not have lunch anywhere except in that restaurant.（他總是嚴格地9點上床睡覺.星期日總在那家飯店吃午飯.）
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