A in case 后接一般现在时、一般过去时或 should。(参见第节。)它看上去与if的用法相似而且常常和if相混淆,但两者完全不同。
in case引导的从句为主句的动作提供理由:
Some cyclists carry repair outfits in case they have a puncture.
有些骑自行车的人携带修理工具,以备万一车胎被扎破。相当于:
Some cyclists carry repair outfits because they may have/because it is pos- sible they will have a puncture.
有些骑自行车的人携带修理工具,因为他们的车胎可能会被扎破。
I always slept by the phone in case he rang during the night.
我总是睡在电话机旁边,惟恐他夜间打电话来。相当于:
I always slept by the phone because (I knew)he might ring during the night.
我总是睡在电话机旁,因为我知道他可能夜间打电话来。
in case从句可以省掉而不改变主句的含义。然而在条件句中,主句的动作依赖于if从句的动作,如果省掉if从句主句的含义就变了。
请比较以下句子:
(a) Bill: Ill come tomorrow in case Ann wants me.
比尔:明天我要来,以备安找我。
(b) Tom: Ill come tomorrow if Ann wants me.
汤姆:如果安找我,我明天就来。
在句子(a)中,安也许要找比尔,也许不找。但比尔无论如何要来。他的行动不取决于安的动作,因此可以把 in case Ann wants me 省掉而不改变主句的含义。
句子(b)是一个条件句,汤姆的到来是以安的要求为条件的。他的动作取决于安的动作。不能省掉 if Ann wants me 而又不改变主句的含义。
B in case从句通常位于主句之后而不是之前。
但要注意 in case of+名词等于 if there is a/an+名词:
In case of accident phone 999.相当于:
If there is an accident phone 999.
如果发生事故,请拨电话999。
if从句和 in case从句之间的混淆可能是由此引起的。
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