if 既可以引导宾语从句又可以引导状语从句。 if 充当宾语从句的连接词时,相当于 whether ,
词义为“是否” ,遵循宾语从句的时态规则;充当从属连词,引导条件状语从句时,词义为
“如果” ,若主句中的谓语动词用一般将来时,则从句中的谓语动词通常用一般现在时表示
将来。
例如: {1} I will go out tomorrow if it is fine.
{2} I don't know if the train has arrived.
句 {1} 中 if 引导的是状语从句。 这个从句表示 “条件” , 修饰主句。 整个句子的意思是 “如
果明天天气好,我们就出去。 ”句 {2} 中 if 引导的是宾语从句,充当谓语动词 don't know 的
宾语。整个句子的意思是“我不知道火车是否到了。 ”
虚拟语气在条件状语从句中的用法
表示与现在事实相反的情况,其句型为“ if+ 主语 + 动词的过去式( be 动词用
were ) ,主语 +would / could / might / should + 动词原形” 。如:
If the weather were fine, we would go to Shanghai.
如果天气好,我们就去上海。 (事实上天气不好)
If they had time, they would / could / might go with me.
如果他们有时间,他们就会(可能)和我一起去。
表示与过去事实相反的情况。 其句型为 “ if + 主语 + 动词的过去完成式, 主语 +would
/ could / should / might + have + 动词的过去分词” 。如:
If I had taken his advice, I shouldn't / wouldn't / couldn't have made such a mistake.
如果我按照他的建议去做,我一
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