时间或条件状语从句不能用将来时态

由when, as soon as, before, after, as, until等引导的时间状语从句以及由if, unless, as long as, in case等引导的条件状语从句不能直接用将来时态，遇此情况英语习惯上用一般现在时代替一般将来时。如：

趁早动手，免得忘了。

误：Do it before you will forget.

正：Do it before you forget.

我到达那儿后就给你写信。

误：I’ll write to you after I will get there.

正：I’ll write to you after I get there.

如果他来，请告诉我一声。

误：In case he will come, let me know.

正：In case he comes, let me know.