As if与将来事实相反的虚拟语气， 谓语用would could might+动词原形。
He opened his mouth as if he would see something.
It looks as if it might snow.
Tom raised his hands as if he would say something.
As if从句也可以与现在事实相反， 谓语动词用一般过去时。
You look as if you didn't care.
It seems that it were spring already.
As if从句与过去事实相反，谓语动词用过去完成时。
He talked as if he knew what had happened.
The girl listened as if she had been turned to the stone.
