as

1、文法不同：as if引导的方式状语从句或表语从句，用虚拟语气;as though表示与现在事实相反，谓语动词，用would(might,could)+动词原形。2、时态不同：as if表示与过去事实相反，用过去完成时;as though表示将来的可能性不大，用一般过去时。3、语境不同：as if用来描述比较悲惨的境遇或者状况;as though语境属于中性，可以用到很多情境中。

用法

例句：He acts as if he knew me.他显得认识我似的。

例句：They treat me as though I were a stranger.他们待我如陌生人。

例句：This meat tastes as if it has already gone bad.这肉吃起来似乎已经坏了。

例句：I feel as though I’m floating on air.他感到好像漂浮在空中。

例句：It is not as if he were poor.他不像穷的样子。

例句：It is not as though you were going away for good.又不是你离开不回来了。