一、基本用法

以as if (as though)引導的方式狀語從句或表語從句，有時用虛擬語氣，若表示與現在事實相反，謂語動詞用一般過去時；若表示與過去事實相反，用過去完成時；表示將來的可能性不大，用would (might, could)+動詞原形。如：

He acts as if he knew me. 他顯得認識我似的。

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

He talks as if he had been abroad. 他說起話來好像曾經出過國。

二、用法注意

(1) 從句所表示的內容若為事實或可能為事實，也可用陳述語氣。如：

It looks as if we’ll be late. 我們似乎要遲到了。

This meat tastes as if it has already gone bad. 這肉吃起來似乎已經壞了。

在現代英語中，有時即使從句內容不是事實，也可能用陳述語氣。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. 玩具狗叫起來像真狗。

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

It isn’t as if he were poor. 他不像窮的樣子(或他又不窮)。

It isn’t as if you were going away for good. 又不是你離開不回來了。