如题所述
ought to 侧重反映客观情况，多在涉及到法律、道义、责任、义务或原则时使用。如 One ought not to cross the street against the red light【人们不该在红灯时过马路】。
外部权威的建议用should
例：The manual says that the computer should be disconnected from the power supply before the cover is removed.
用主语I给他人建议的时候，用should或would而不是ought to
例：I should leave early tomorrow, if i were you.
wh疑问词引导的的问句用should
例：What should I do if I have any problems?
should/ought to+have+过去分词表示过去没发生并对此感到遗憾的事情
例：We should/ought to have waited for the rain to stop. （说明没等）
提供帮助或要求确认或建议的问句用should或shall
例：Should I phone for a taxi for you?
口语中表示我们觉得最好应该做某事的时候用had better比用should/ought to更合适，但是过去时中和提到大众规则时不能用had better
例：If you're not well, you'd better ask Clare to go instead. （或者...you should/ought to...）
I don't think parents should/ought to give children sweets. （不能用...parents had better give...）
在紧急情况、需求、威胁的情况下用had better
例：There's someone moving about downstairs. We'd better call the police, quickly.
had better的否定是had better not，疑问句中had先行
例：He'd better not be late again or he'll be in trouble.
Had we better get a taxi? （或者Should we get...?）
表示“劝告”，“建议”或“义务”时，译作“应当”，
He
should
take
care
of
his
parents
as
they
are
old
enough
not
to
live
on
themselves.
由于父母亲老了，不能自理，他应当照顾他们。
ought
to，接动词原形表示“有义务”或“必要”做某事，译为“应当，应该”
2．should
have
done在虚拟语气中表示“责备或后悔””
ought
to
have
done
sth,
should
have
done
sth
本应该做某事，而事实上并没有做。否定句表示"不该做某事而做了"。
You
ought
to
(should)
have
been
more
careful
in
this
experiment.
He
ought
not
to
have
thrown
the
old
clothes
away.（事实上已扔了。）
3．在这两个方面，用法基本相同，ought
to
在语气上比should
要强。
4．Should还表示“预测”和“可能”
He
should
be
there
now.
他可能到了。
5．Should在虚拟语气的用法中，用于从句中。
1）
It
is
demanded
/
necessary
/
a
pity
+
that…结构中的主语从句的谓语动词要用should
加动词原形，
should
可省略。
句型：
(1)suggested
It
is
(2)important
that…+
(should)
do
(3)
a
pity
(1)suggested,
ordered,
proposed,
required,
demanded,
requested,
insisted；
+
(should)
do
(2)important,
necessary,
natural,
strange
a
pity,
a
shame,
no
wonder
(3)It
is
suggested
that
we
(should)
hold
a
meeting
next
week.
It
is
necessary
that
he
(should)
come
to
our
meeting
tomorrow.
2）在宾语从句中的应用
在表示命令、建议、要求等一类动词后面的从句中。
order,
suggest,
propose,
require,
demand,
request,
insist,
command,
insist
+
(should)
do
I
suggest
that
we
(should)
hold
a
meeting
next
week.
He
insisted
that
he
(should
)
be
sent
there.
