2. 注意in case 后从句的时态

(1) 原则上说，若主句为现在时态，则从句也用现在时态；主句为过去时态，从句也用过去时态。如：

I always keep candles in the house in case there is a power cut. 我家里常备有蜡烛，以防断电。

I wrote down her address in case I forgot it. 我记下了她的住址，免得忘了。

He wasn’t going to use his car in case somebody recognized it. 他不打算用自己的汽车，因为怕有人认出他的车。

(2) 有时从句也可用“should+动词原形”这样的虚拟语气（不管主句为现在时态还是过去时态）。如：

I don’t let him go out in this weather in case he should catch cold. 我不让他这种天气出去以防他会感冒。

I’ve bought a chicken in case your friend should stay to lunch. 我买了一只鸡，免得你的朋友万一留下来吃午饭没菜。

(3) 注意，当主句为将来时态时，从句谓语不能用将来时态，而要用一般现在时表示将来意义。如：

I’ll keep a seat for you in case you change your mind. 我给你留一个座位，以防你会改变主意。

3. 不要混淆in case 与in case of

in case 可用作连词和副词，而in case of 用作介词。如：

In case of fire, ring the bell. 如发生火灾，请按铃。(from www.nmet168.com)

The wall was built along the river in case of floods. 沿江筑了堤坝以防有洪水。

有时两者可以互相转换。如：

In case I’m not here, ask my brother to help you.=In case of my not being here, ask my brother to help you. 如果我不在，可让我弟弟帮助你。

4. 弄清in case与if的区别

注意下面两个句子在意思上的不同：

I’ll come tomorrow in case Ann wants me. 明天我要来，以备安找我。

I’ll come tomorrow if Ann wants me. 如果安找我，我明天就来。

但是，介词短语 in case of…与 if there is…的意思却相同。如：

In case of accident phone 999.=If there is an accident phone 999. 如果发生事故，请拨电话999。

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