表示在将来不太可能实现的条件从句有三种形式：
①were、did
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。
If she had time, she could help me.她要是有时间，就会帮我了。
②should 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。
③were 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。
If I 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。
If the headmaster were to come, what would we say to him假如校长来了，我们对他说什么呢？
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）
If it 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）