could可以語氣較委婉 較輕
should應(yīng)該有點上對下的語氣較強硬.
I wish you would stay.
我希望你能留下來
Used to make a polite request:
用于有禮貌的請求：
Would you go with me?
你愿意和我一起去嗎?
Used to indicate uncertainty:
表示不確定之意：
It would seem to be getting warmer.See Usage Note at if
天氣似乎變得更暖和了參見 if
would
[wEd, wJd]
v.
（略寫為'd,否定式的略寫為 wouldn't [wJd(E)nt] ）
(will 的過去式）
They said it would be fine.
聽說天氣會很好.
I would give anything to see the film.
假如可能的話,我怎么也要看一看這部電影.
Would you like some cake or biscuit?
你要吃點蛋糕還是并干?
He said he would come.
他說他要來.
（表示過去的習(xí)慣）常,有…的習(xí)慣
She would lose the key!
她總是把鑰匙弄丟了.
would rather
寧可…也不；寧愿
Which would you rather do, go to cinema or stay at home?
你是去看電影還是待在家里?
Would rather die than surrender.
寧死不投降.
I could run faster then. It could be no better at that time. Only men could go to the club in those days.
那時我能跑得更快.那時好得不能再好了.在當(dāng)時,只有男人可以去俱樂部
Used with hypothetical or conditional force:
用來表推測或條件：
If we could help, we would.
如果我們能幫上忙,我們會幫的
Used to indicate tentativeness or politeness:
用于表示試探性或禮貌：
I could be wrong. Could you come over here?
我也許錯了.你能到這邊來嗎?
could
[kJd]
v.
動詞 can 的過去式
I could run faster then.
我那時能跑得更快一些.
（表示與事實相反的設(shè)想）能；可以
I could come tomorrow if you like.
如果你愿意,明天我可以來.
（委婉語）能
Could you do sth. for me?
你能替我做件事情嗎?
應(yīng)該
You could at least have met me at the station.
你至少應(yīng)該到車站來接我.
可能
I wrote down the number so that I could remember it.
我寫下了號碼,那樣我就能記住它了.
You should send her a note.
你應(yīng)該給她留一個條
Used to express probability or expectation:
用于表示可能性或期望：
They should arrive at noon.
她應(yīng)該在中午到達(dá)
Used to express conditionality or contingency:
用于表示可能性或可能發(fā)生的事件：
If she should fall, then so would I.
如果她失敗了,那我也會失敗
Used to moderate the directness or bluntness of a statement:
用于使一個直接或直率的陳述變得婉轉(zhuǎn)：
I should think he would like to go.
我倒是認(rèn)為他愿意去
Like the rules governing the use of shall and will on which they are based, the traditional rules governing the use of should and would are largely ignored in modern American practice. Either should or would can now be used in the first person to express conditional futurity:
就象作為shall 和 will 詞的基礎(chǔ)的限用的用法規(guī)則一樣, 適用于should 和 would 這個詞的傳統(tǒng)使用規(guī)則在現(xiàn)代美國英語中也已被忽略了. 現(xiàn)在should 或 would 這兩個詞中的任何一個都可以用于第一人稱,表示條件式中的將來：
If I had known that, I would (or somewhat more formally, should ) have answered differently.
如果已經(jīng)知道了這個情況的話,我就（或正規(guī)一點用 should ） 不會那么回答了 ,
But in the second and third persons only would is used:
但在第二人稱或第三人稱中只用would ：
If he had known that, he would (not should ) have answered differently.
如果他知道那個情況的話,就（不能用 should ） 不會那么回答了.
Wouldcannot always be substituted for should, however. Should is used in all three persons in a conditional clause:
但是Would并不是總是能由 should 代替. Should 在三種人稱的條件從句中都可以用：
if I (or you or he ) should decide to go.
如果我（或 你 或 他 ） 決定要去.
Should is also used in all three persons to express duty or obligation (the equivalent of ought to ):
Should用于這三種人稱的表示職責(zé)和義務(wù)的句子中（相當(dāng)于 ought to ）：
I (or you or he ) should go.
我（或者 你 或者 他 ） 應(yīng)該去 .
On the other hand, would is used to express volition or promise:
另一方面,would 用來表達(dá)決心或保證：
I agreed that I would do it.
我一定會做的.
Either would or should is possible as an auxiliary with like, be inclined, be glad, prefer, and related verbs:
而would 或 should 都可以作助詞和 like,be inclined, be glad,prefer 及其相關(guān)詞語一起使用：
I would (or should ) like to call your attention to an oversight.
我想（或 should ） 請你注意一下一個疏漏之處 .
Here would was acceptable on all levels to a large majority of the Usage Panel in an earlier survey and is more common in American usage than should. · Should have is sometimes incorrectly written should of by writers who have mistaken the source of the spoken contraction should've. See Usage Note at if, rather, shall
在此處,在一次早期的調(diào)查中對大多數(shù)各階層的使用者來說,would 是可以接受的, 且在美國用法中比should 更為常見. 有時書寫者把should have 誤拼成 should of , 因為他們把口頭縮略形式should've的來源給弄錯了 參見 if, rather, shall
should
[Fed, FJd]
v.aux.
否定式縮略為 shouldn't
（用于間接引語,表示）將
We said we shouldn't arrive till 6.
我們說過我們六點才能到.
"If it should rain tomorrow, the sports meeting would be postponed."
"要是明天下雨,比賽就延期舉行."
（和that一起用于表示意愿的動詞和形容詞之后）
He was keen that she should go to college.
他渴望她能上大學(xué).
（在條件句中與第一人稱連用） 可能；會
I should have bought it if I had enough money.
如果當(dāng)時我有足夠的錢,我會把它買下來的.
（表示責(zé)任或義務(wù)）必須,應(yīng)該
Children should obey their parents.
兒童應(yīng)該服從他們的父母.
He should have known that the police would never allow this sort of thing.
他本應(yīng)知道這樣的事情警察是決不允許的.
（表示可能之事）可 能
It should be fine tomorrow.
明天可能天晴.
（表示不確定）萬一
If I should see him, I'll tell him.
萬一我見到他,我就告訴他.