表示在将来不太可能实现的条件 从句有三种形式：
① 条件从句用动词的过去式（be动词用were）,主句用should（第一人称）或would（全部人称）+动词原形.也可用could,might代替should, would.
If he were here tomorrow, I would speak to him. 明天如果他在这里的话,我就和他谈谈.
If you dropped the glass, it would break. 你要是把杯子掉下来,会打碎的.
② should do
条件从句中不管什么人称都用should do,可表示有偶然实现的可能性.
If it should rain, the crops could be saved. 假如下雨,庄稼可能就有救了.
We would trust him if he should be honest. 如果他真是诚实的,那我们就相信他.
③ were to do
条件从句用were + to do.这种形式比较正式,常出现在书面语中,其假设成份很大,实现的可能性很小.
IfI were to do the work, I should do it in a different way. 要是我做这项工作,我就会以不同的方式去做.
对比：
将来不太可能实现的三种非真实条件句中的虚拟语气对比
If it snowed tomorrow, I would stay at home. 如果明天下雪的话,我就留在家里.
（常用形式）
If it should snow tomorrow, I would stay at home. 如果明天下雪的话,我就留在家里.
（可能性较小）
Ifit were to snow tomorrow, I would stay at home. 如果明天要下雪的话,我就留在家里.（可能性最小）