as if 连接的从句,即可表示对现在、将来时间的虚拟,又可以是对过去时间的虚拟。
基本用法
as if 从句用虚拟语气，当说话人认为句子所述的是不真实的或极少有可能发生或存在的情况时。从句虚拟语气动词时态的形式如下：
1、如果从句表示与现在事实相反，谓语动词用一般过去时。
2、从句表示与过去事实相反，谓语动词用“had＋过去分词”。
3、从句表示与将来事实相反，谓语动词用“would／could／might＋动词原形”。例如：
You look as if you didn’t care．你看上去好像并不在乎。
He talks about Rome as if he had been there before．他说起罗马来好像他以前去过罗马似的。
He opened his mouth as if he would say something．他张开嘴好像要说什么。
两点说明
1.从句所表示的内容若为事实或可能为事实，也可用陈述语气。
It looks as if we'll be late.我们似乎要迟到了。
This meat tastes as if it has already gone bad.这肉吃起来似乎已经坏了。
在现代英语中，有时即使从句内容不是事实，也可用陈述语气。
I feel as if I'm floating on air.他感到好像漂浮在空中。
The stuffed dog barked as if it is a real one.玩具狗叫起来像真狗。
2.注意It isn't as if的翻译
It isn't as if…是英语中的固定句式，也可说成 It’s not as though，主要用于表示某个解释不正确，意思是“好像不是”“显然不是”“真不是”等。
It isn't as if he were poor. 他不像穷的样子（他又不穷）。
It isn’t as if he didn’t recognize me! He just walked straight past me as I stood there. 他不像是没认出我！可是我站在那里他迳直从我跟前走过。
as if 从句的作用
1.在look，seem等系动词后引导表语从句。
She looks as if she were ten years younger.
她看起来好像年轻了十岁。
2.引导方式状语从句
She loves the boy as if he were he father.
她爱这个男孩，就好像他是她的父亲一样。
as if还可用于省略句
如果as if引导的从句是“主语+系动词”结构，可省略主语和系动词，这样as if后就只剩下名词、不定式、形容词（短语）、介词短语或分词。
He acts as if (he were)a fool.
他做事像个傻子。
She left the room hurriedly as if (she were)angry.
她匆忙离开房间好像生气的样子。
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