as though = as if = as it/one would be if 或者as it/one would do if

其中，as引导方式状语从句，该从句本身又是个带有 if 虚拟条件句的主从复合句，所以 as 后的it/one 后用虚拟语气形式 would be/do。例如

He ran as if ghosts were chasing him.

= He ran as he would do if ghosts were chasing him.

He looks as if he had seen a ghost.

= He looks as he would be if he had seen a ghost.