1. 在look, seem 等系动词后引导表语从句。
2. 引导方式状语从句。
3. as if 还可用于省略句中，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。
扩展资料
例句：
I had a sensation of falling, as if in a dream.
我有一种坠落的感觉，像在梦中似的。
I dont feel as if I belong here.
我在这里感觉格格不入。
I felt as if my heart had stopped.
我觉得好像我的心都不跳了。
I ate as if there was no tomorrow.
我狼吞虎咽地吃着。
He suddenly appeared as if by magic.
他突然神奇地出现了。
