一、基本用法

以as if (as though)引导的方式状语从句或表语从句，有时用虚拟语气，若表示与现在事实相反，谓语动词用一般过去时；若表示与过去事实相反，用过去完成时；表示将来的可能性不大，用would (might, could)+动词原形。如：

He acts as if he knew me. 他显得认识我似的。

They treat me as though I were a stranger. 他们待我如陌生人。

He talks as if he had been abroad. 他说起话来好像曾经出过国。

二、用法注意

(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。如：

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，也可能用陈述语气。如：

I feel as if [as though] I’m floating on air. 他感到好像漂浮在空中。

The stuffed dog barked as if it is [were, was] a real one. 玩具狗叫起来像真狗。

(2) 注意 It isn’t as if…的翻译。如(from www.nmet168.com)：

It isn’t as if he were poor. 他不像穷的样子(或他又不穷)。

It isn’t as if you were going away for good. 又不是你离开不回来了。