unless和if not的区别是什么?

它们不是同义词么?能否在所有情况下互换?

最佳答案
本回答由达人推荐

大海 9级
2010-01-08 回答
unless在意义上相当于if…not…,因此在有些场合if…not…可为unless所代替。
但在有些场合又不能互换,我们要注意下面几种情况:
1.当if…not…引导非真实条件分句时,一般不可改用unless。 例如:
If she had not had an alarm clock,she would have missedthe train.(事实:她有闹钟。)
如果把上述例句中的if…not…换成unless,意义就相反了。
(误)Unless she had had an alarm clock, she would havemissed the train.(事实:她没有闹钟)
2.If…not…引导的条件分句可以重叠使用,unless则不可, 因为unless表示唯一条件。例如:
She won't lose weight if she doesn't keep a diet and ifshe does not take exercise every day.
3.unless引导的分句可用否定结构,而if…not …引导的分句不可再否定。例如:
Don't ask me to explain unless you really don't understand.
The directors have a meeting every Friday,unless there is nothing to discuss.
以上两例句中的unless不可换成if…not…。
4.在unless引导的肯定形式的条件分句中, 通常用肯定词(即some,already,still,too,as well等),在if…not…引导的分句中,通常用非肯定词(即any,yet,ever,either,at all等)。例如:
I will criticize you if you haven't spoken to her yet.
I will criticize you unless you have already spoken to her.
(误)…unless you have spoken to her yet.
不过在否定形式的非真实条件分句中,if…not …结构仍能与肯定词连用。例如:
If he hadn't already prepared his lesson, he wouldn't beallowed to go.(因为这种从句表面上是否定,实际上是肯定。)
5.在间接引语中,当if=whether,意为“是否”,unless 不可以代替if…not…。例如:
She promised to let me know if she wasn't coming.
6.当unless含有“除了”的意思,不可为if…not…所替代。例如:
He never stammers,unless when he is angry.( unless when=except when)
Nothing will come out of it, unless disaster.(unless=except)
7.当主句是疑问句时,不可用unless代替if…not…。 因为unless用在A情况发生,必导致B结果之类的复合句中。例如:
What shall we do it they don't reply to our letters?
8.当主句谓语是be+某些形容词或分词,如:glad,surprised,disappointed,satisfied,ashamed,delighted和pleased等, 不可用unless代替if…not…。例如:
I'll be really surprised if they don't come to the meeting.
I'll be quite glad if she doesn't join them.
之所以不能为unless代替,是强调否定条件的出现,表明在这种前题下的因果关系。以上条件状语从句都可变为原因状语从句。例如:
I'll be really surprised that they won't come to the meeting.
这里if被that代替了,而从句的否定结构不变。
综上所述,unless既等于if…not…,在某些场合又不相等, 因此要牢记它们之间的差别,准确地使用它们。

最新回答 (4条回答)

三花 6级
2010-01-08 回答
unless在意义上相当于if…not…,因此在有些场合if…not…可为unless所代替。
但在有些场合又不能互换,我们要注意下面几种情况:
1.当if…not…引导非真实条件分句时,一般不可改用unless。 例如:
If she had not had an alarm clock,she would have missedthe train.(事实:她有闹钟。)
如果把上述例句中的if…not…换成unless,意义就相反了。
(误)Unless she had had an alarm clock, she would havemissed the train.(事实:她没有闹钟)
2.If…not…引导的条件分句可以重叠使用,unless则不可, 因为unless表示唯一条件。例如:
She won't lose weight if she doesn't keep a diet and ifshe does not take exercise every day.
3.unless引导的分句可用否定结构,而if…not …引导的分句不可再否定。例如:
Don't ask me to explain unless you really don't understand.
The directors have a meeting every Friday,unless there is nothing to discuss.
以上两例句中的unless不可换成if…not…。
4.在unless引导的肯定形式的条件分句中, 通常用肯定词(即some,already,still,too,as well等),在if…not…引导的分句中,通常用非肯定词(即any,yet,ever,either,at all等)。例如:
I will criticize you if you haven't spoken to her yet.
I will criticize you unless you have already spoken to her.
(误)…unless you have spoken to her yet.
不过在否定形式的非真实条件分句中,if…not …结构仍能与肯定词连用。例如:
If he hadn't already prepared his lesson, he wouldn't beallowed to go.(因为这种从句表面上是否定,实际上是肯定。)
5.在间接引语中,当if=whether,意为“是否”,unless 不可以代替if…not…。例如:
She promised to let me know if she wasn't coming.
6.当unless含有“除了”的意思,不可为if…not…所替代。例如:
He never stammers,unless when he is angry.( unless when=except when)
Nothing will come out of it, unless disaster.(unless=except)
7.当主句是疑问句时,不可用unless代替if…not…。 因为unless用在A情况发生,必导致B结果之类的复合句中。例如:
What shall we do it they don't reply to our letters?
8.当主句谓语是be+某些形容词或分词,如:glad,surprised,disappointed,satisfied,ashamed,delighted和pleased等, 不可用unless代替if…not…。例如:
I'll be really surprised if they don't come to the meeting.
I'll be quite glad if she doesn't join them.
之所以不能为unless代替,是强调否定条件的出现,表明在这种前题下的因果关系。以上条件状语从句都可变为原因状语从句。例如:
I'll be really surprised that they won't come to the meeting.
这里if被that代替了,而从句的否定结构不变。
综上所述,unless既等于if…not…,在某些场合又不相等, 因此要牢记它们之间的差别,准确地使用它们。
2010-01-08 回答
if not表示不然的话,否则。后面不接句子,应该接短语,如If not his help, I would have failed. 
Unless表示除非,如: 
My baby sister never cries unless she is hungry. 
我刚出生的妹妹除非饿了,她是从来不哭的。 
I shall go there tomorrow unless I'm too busy. 
如果我不太忙,明天将到那儿去。 
Unless you go at once you will be late. 
如果你不马上走,就会迟到的
→Eila 3级
2010-01-08 回答
两者都可表示否定的条件,有时可换用。如: Come tomorrow unless I phone [if I don’t phone]. 要是我没有打电话,明天就来。 You won’t catch the train unless you hurry [if you don’t hurry]. 你要是不赶快,你就赶不上火车了。 但是在下列情况下,通常要用 if ... not 而不用 unless: 1. 当所述条件要引出一种新的想法或情况(而不是结束已存在的想法或状态)时。如: I’ll be angry if I’m not invited to the party. 如果不邀请我参加晚会,我会生气的。(即“不邀请我去参加晚会”会导致一种新情况——“我会生气”) I will be surprised if he doesn’t have an accident. 他要是不出事,我倒感到奇怪了。(即“他不出事”会导致一种新情况——“我感到奇怪”) 2. 当要引出一个表示假想的(imaginary)条件句时。如: If he weren’t so silly, he would understand. 他要不是那样傻的话,他就会明白了。(实际上他很傻) If I hadn’t stopped her, she would have jumped down. 要不是我阻止了她,她就跳下去了。(实际上我阻止了她) 注:偶尔可见到 unless 用于假想条件句,但有不少语法家反对这一用法,建议学生不要模仿。顺便说一句,unless 有时用于引出一个补充前言的话(此时通常用破折号而不用逗号且不能用 if ... not 替换),此时若谈论的是过去的情况,注意不要与表示想象的条件句相混淆。如: I couldn’t have got to the meeting on time — unless I had caught an earlier train. 我不可能及时赶到会场,除非我赶上了较早的一班火车。(事实是“我”没有及时到会) 若将上句中的 unless 换为 if ... not,则意思有很大差别: I couldn’t have got to the meeting on time if I had not caught an earlier train. 要是我没有赶上早一班火车,我就不可能及时到会了。
2010-01-08 回答
基本木区别