should
should
v.aux.（助动词）
shall的过去式
Used to express obligation or duty:
应该：用来表示义务或职责：
You should send her a note.
你应该给她留一个条
Used to express probability or expectation:
用于表示可能性或期望：
They should arrive at noon.
她应该在中午到达
Used to express conditionality or contingency:
用于表示可能性或可能发生的事件：
If she should fall, then so would I.
如果她失败了，那我也会失败
Used to moderate the directness or bluntness of a statement:
用于使一个直接或直率的陈述变得婉转：
I should think he would like to go.
我倒是认为他愿意去
Like the rules governing the use ofshall and will on which they are based, the traditional rules governing the use ofshould and would are largely ignored in modern American practice. Eithershould or would can now be used in the first person to express conditional futurity:
就象作为shall 和 will 词的基础的限用的用法规则一样， 适用于should 和 would 这个词的传统使用规则在现代美国英语中也已被忽略了。 现在should 或 would 这两个词中的任何一个都可以用于第一人称，表示条件式中的将来：
If I had known that, I would (or somewhat more formally, should ) have answered differently.
如果已经知道了这个情况的话，我就（或正规一点用 should ） 不会那么回答了 ，
But in the second and third persons onlywould is used:
但在第二人称或第三人称中只用would ：
If he had known that, he would (not should ) have answered differently.
如果他知道那个情况的话，就（不能用 should ） 不会那么回答了。
Wouldcannot always be substituted for should, however. Should is used in all three persons in a conditional clause:
但是Would并不是总是能由 should 代替。 Should 在三种人称的条件从句中都可以用：
if I (or you or he ) should decide to go.
如果我（或 你 或 他 ） 决定要去。
Should is also used in all three persons to express duty or obligation (the equivalent of ought to ):
Should用于这三种人称的表示职责和义务的句子中（相当于 ought to ）：
I (or you or he ) should go.
我（或者 你 或者 他 ） 应该去 。
On the other hand,would is used to express volition or promise:
另一方面，would 用来表达决心或保证：
I agreed that I would do it.
我一定会做的。
Eitherwould or should is possible as an auxiliary with like, be inclined, be glad, prefer, and related verbs:
而would 或 should 都可以作助词和 like，be inclined， be glad，prefer 及其相关词语一起使用：
I would (or should ) like to call your attention to an oversight.
我想（或 should ） 请你注意一下一个疏漏之处 。
Herewould was acceptable on all levels to a large majority of the Usage Panel in an earlier survey and is more common in American usage thanshould. · Should have is sometimes incorrectly written should of by writers who have mistaken the source of the spoken contractionshould've. See Usage Note at if ,rather ,shall
在此处，在一次早期的调查中对大多数各阶层的使用者来说，would 是可以接受的， 且在美国用法中比should 更为常见。 有时书写者把should have 误拼成 should of ， 因为他们把口头缩略形式should've的来源给弄错了 参见 if,rather,shall
should
[Fud, FEd, Fd]
v.aux.
(shall 的过去式)
[表示过去将来时; 常用于间接引语]将
[表示语气较强的假设]万一, 竟然
[用于第一人称时表示某种条件下会产生的结果; 用于第二、三人称时表示说话者的意愿]就, 该
[表示可能性、推测、推论]可能, 该
[表示义务、责任]应当, 应该
[表示委婉、谦逊]可, 倒
[用于表示必要、适当、惊奇、遗憾等的从句中]应该; 竟然会
[与why, who, how 等连用, 表示意外、惊异等] 竟会
[用于表示建议、命令、决定等的从句中]应该, 必须
[用于表示目的或由 lest 等引导的从句中]可以, 会; 万一
[用于让步状语从句中]即使
I told you I should be glad to do it. (=I told you, “I shall be glad to do it.”)
我告诉过你, 我是高兴去做的。
If I should fail I would try again.
万一失败, 我还要试一试。
If you [he] had much money, you [he] should buy it.
如果你[他]有许多钱, 你[他]就该把它买下来。
They should have arrived in Beijing by this time.
他们这个时候该到北京了。
You shouldn't be so careless.
你不应该这样粗心大意。
I should hardly think so.
我倒并不那样想。
It is simply a miracle that rice should grow in such a place.
稻子竟能在这样的地方生长, 这实在是个奇迹。
How should I know?
我怎么会知道呢?
It was proposed that we should act at once.
有人提议我们必须立刻行动。
I'll remind him lest he should forget it.
怕他忘记, 我会提醒他的。
I stayed in lest I should catch cold.
我怕伤风, 所以呆在屋里。
S-he fail, he would try again.
万一失败了, 他会再试一试的。
参考资料：金山词霸