as if he{knew knows

英国著名语言学家 R. Quirk 等人在 A Grammar of Contemporary English 中曾举过这样的例子：

He treats me as if $\$left\{ \begin{array}{l} \text{I'm} \\ \text{I were} \end{array} \right\} a stranger. (GCE, p. 755)

他们解释道：“The use of the hypothetical past makes little difference here, since both the present and past form imply the unreality of what is expressed in the subordinate clause; it is assumed from both sentences that ‘I am not a stranger’.”

（“这里用不用假设过去时，并没有什么区别，因为现在形式和过去形式都表明 as if 从句所表达的内容是非真实的，即两个分句都含有‘I am not a stranger.’的意思。”）

这就是说,当从句意可以明显地看出 as if 从句所表达的内容是非真实的时候,使用陈述语气或使用虚拟语气是没有什么区别的。请看下面的例句:

1. He talks as if $\$left\{\begin{array}{l} he has \\ he had \end{array}\right\} a potato in his mouth. (CGEL) (这两个句子都意味着“他嘴里并没有真的含着一个土豆”) 他说起话来就好像嘴里含着一个土豆似的。

2. The stuffed dog barks as if it is a real one. (CGEL) 这个狗标本叫起来像真狗似的。

3. Suddenly, the knocking turned to a forceful banging, as if someone were hitting the door with a metal rod. (Dan Brown, The Da Vinci Code) 突然, 敲门声变成了沉重的撞击声, 仿佛有人在用铁棒砸门。(《达·芬奇密码》)