■ unless

1) unless 最常见的用法，是从句用一般现在时，主句用一般现在时或一般将来时，表示“除非…，否则就…”。所需条件（不可缺少的必要条件）是有可能实现的，因而结果也有可能在现在或者在将来实现。

• Sally says she won't wait for you unless you hurry up. (W. Somerset Maugham, Of Human Bondage)萨利说，你如果不赶快，她就不等你了。

有时候这个 unless 从句中的一般现在时也可以改为表示虚拟的动词原形，更加强调这是有待实现的条件。

• Sin is not forgiven unless restitution be made. (Saint Augustine, Ep. cliii ad Macedon.)除非作出补救，否则罪孽不得赦免。

如果所需条件是过去的，则也可以再 unless 从句中用一般过去时。

• She would be here by now unless she was stuck in the traffic.她除非交通受阻，要不然现在该到了。

整个坐标移到过去，从句用一般过去时，主句用过去将来时，所需条件过去有可能实现，结果也有可能在过去或过去将来实现。

• He was told he couldn't get a job unless he had a high school degree.人家告诉他，除非有高中毕业文凭，否则他是找不到工作的。

2) 如果对于所需条件能否实现有较大的怀疑，因而结果能否实现也没有把握，可以在从句中不用直陈式一般现在时而用虚拟式动词，在主句中不用直陈式现在或一般将来时而用 would + inf. 的条件式。

• That little time with lyre and rhyme
  To while away—forbidden things!
  My heart would feel to be a crime/Unless it trembled with the strings. (Edgar Allen Poe, Poems, 1829)那段有七弦琴和韵律伴随着的短促时光
  消磨掉——犯禁的事物！
  我的心会感到是个罪恶／除非它随着琴弦颤抖。
• Tzu-hsia said, "A gentleman lays no burdens on the people until they have learned to trust him. Unless they trusted him they would think him cruel. Until he is trusted he does not reprove. Unless he were trusted it would seem fault-finding." (Sayings of Confucius, English version by Legge)（《论语》）子夏曰：“君子信而后劳其民；未信则以为厉己也。信而后谏；未信则以为谤己也。”

如果所需条件在时间上要先于结果，unless 从句的谓语动词要采用过去完成时态。

• He also claims that under the agreement the film would not be shown unless he had signed a release form.他又声称，除非他签署过公演书，否则该影片不能放映。

2) unless 也可以用来客观叙述过去习惯行为当中的例外，此时主句和从句都用一般过去时，所表示的都是事实，没有假定成分。

• He did not work for me unless he had no work to do for others.他除非在别人那里没有工作做，否则他是不到我这里工作的。
• Unless he was very ill, he would be at work.他除非病得很厉害，否则都是在工作。
• Every evening, unless he had a visitor, he rode round the city for two hours on a bus.每天黄昏，他除非有人来访，否则总是乘坐公共汽车在市里兜两小时的风。

4) unless 可以用于从现在的角度对过去尚未确定的事情进行推论，此时从句谓语用一般过去时或过去完成时。

• We do not know why this did not happen, unless he had fallen into disfavor.这件事情为什么没有发生，我们现在不清楚，除非是他失了宠。

5) unless 还可以站在过去当时的角度对当时尚未确定的事情进行推论。

• His jean jacket was soaked with what looked like blood. Unless he had a mortal wound and was hiding it, the blood wasn't his.他的蓝布外套浸透着像是鲜血的东西。除非他是受了致命重伤又掩盖着伤势，否则这些血就不是他的。
• And, indeed, unless this shoal had a machine in its stomach, how could it change its position with such astonishing rapidity? (Jules Verne, 20,000 Leagues Under the Sea)的确，这个沙洲，除非肚子里装着一副机器，否则它怎么能以如此惊人的速度改变位置？
• His letters to her are from places all over the north of England, and are strangely addressed to her as either Gwennie Rogers or G. Rylands. Unless he had another secret, I presume they were both my mother since they all went to the same address in Johnstown, north Wales, or to the store. (Ralph Steadman, Gonzo the Birth)他写给她的信，是从英格兰北部各个地方发出的，奇怪的是：寄给她时，收信人要么是衮妮·罗杰斯，要么是 G·莱兰兹。除非他另有秘密，否则我推论这两个名字都是我母亲的，因为信件全都寄往北威尔士乔治城的同一个地址，或者寄到店里。

如果所需条件要先于结果，它可以用过去完成时来表示。

• By the original law respecting the appointment of a dictator (lex de dictatore creando) no one was eligible for this office, unless he had previously been consul.按照有关如何推举独裁官的原有法律，任何人除非先前担任过执政官，否则没有资格。

6) unless 如果用于表示现在对过去事实的作出反面的假定，则主句（有否定词，因而违反事实）以 unless 从句（本身因 unless 而已经有否定意义）的违反事实为条件。既然主句应该去掉否定词才符合事实，那么，unless 从句内部所说的事应该符合事实，unless 的否定作用应该排除。这样，骤然看来，unless 从句同 if... not... 从句意思是一样的，都是作出违反过去已发生的事实的假设。但是，用 if... not... 从句时，重点落在主句上，是从原因（从句）推论出结果（主句）；而用 unless 从句时，则重点落在从句上，是从结果（主句）推论出原因（从句），肯定从句内部所说的假说符合事实。这两个不同的推论方向，也从主句和从句出现的次序可以看得出来。

• If the elephant hadn't had perfect eyesight, she wouldn't have seen the mouse. = The elephant wouldn't have seen the mouse unless she'd had perfect eyesight.大象要不是眼力好，本来是不会看见耗子的。= 大象看见了耗子，可见它眼力好。

但是，如果从句中用了一些肯定了此事为事实的单词，推论就成为多此一举，就不能用 unless 而只能用 if... not...

• If you hadn't driven so recklessly, you wouldn't have had this accident.要不是你开车开得这么鲁莽，你本来就不会出这个事故。

这里由于有了 so，连鲁莽的程度都明确指出了，就不必再推论是否鲁莽了，所以不能改成使用 unless: *You wouldn't have had this accident unless you had driven so recklessly. 这个句子，如果去掉 so，则 unless 从句还是可以使用。

同样，If you hadn't had that last glass of wine, this would never have happened. 你要不是最后再喝了那一杯酒，这件事情本来不会发生。这句中的 that 已经肯定了的确喝了那杯酒，再用 unless 来推论是否喝了就多此一举，所以不能用 unless 而只能用 if... not... 如果去掉 that last，改为代表新知信息的 a last 或 another，就可以用 unless 从句来表示推导出的结论（有人主张 unless 不能用于违反过去事实的假设，应该改用 if... not...，但是他们举出的只能用 if... not... 的例句，从句中都是有 so 或 that 之类表示已知信息的单词。其实，其所以不能用 unless，并不是 unless 不能用于违反过去事实的假设，而是不能用来推导出一个已知信息作为推理结果；如果用来推导出一个新知信息，还是可以的）。

7) 如果主从句主语相同，unless 从句的主语和谓语动词组的第一个动词可以省略。

• Don't shut down these computers unless (you are) instructed to do so.除非指示你关上这些电脑，否则不要关上。
• Unless (he is) given sufficient warning of the consequences he will continue to misbehave.除非给他发出足够的警告，否则他会继续调皮捣蛋。

不过，这种省略的做法，会使得文体过于正式，日常用语还是保留主语和谓语动词组的第一个动词为好。