关于高一英语从句的问题

We have decided that we would go there by bus. 句子主句是现在完成,从句里也可以用 will. 即
We have decided that we WILL go there by bus.
would 和 will 在这里是语气不同, would 表示可能性小些.will 比较肯定.
请参看 语法 中 有关 虚拟语气 的说明.
我想问的是 为什么有的从句它的主从句时态会不一样 这和我们老师说的不是不一样吗?
不知你们老师怎么说的,主句是现在时,从句可以是各种时态,比如：
I think he will come.
I think he has come.
I think he came yesterday.
主句是过去时,从句要用过去时,过去完成时,过去将来时.
I thought he would come.
I thought he had come.
I thought he came the day before.