BE TO DO 和BE GOING TO DO 有什么区别

都用于将来时.但
be to do 表"必然趋势"
be going to do 表"主观打算"或"一般将来"

一. 小窥 “be to do” 的用法

一般说来， “be to do” 这个结构有两种语法意义，其一是连系动词 be+ 动词不定式做表语，其二是 be to 是一个独立词汇单位 , 具有情态含义 , 可以把它叫做情态习语 (modal idiom) 。

一、 be + 动词不定式 , 不定式做表语 , 表示主语和表语在概念上是等同的。如：
The problem is to find a solution.
His plan is to clean the room.
My wish is to be a doctor.

二、 be to + 动词不定式中的 be to 用作情态习语 , 这时的 be to do 表示 : “ 计划 ” 、 “ 安排 ” 、 “ 义务 ” 、 “ 应该 ” 、 “ 可能 ” 、 “ 命运 ” 等。 (have to, ought to) 。如 :
He is to have a holiday. ( 表示将来 )
The committee is to meet today. ( 表示计划、安排 )
You are to go to the hotel where rooms have already been booked for you.

1. 表示 “ 将 ” 、 “ 计划 ” 、 “ 安排 ” 。 ( 意思接近于 be going to) 如：
Their daughter is to get married soon.
Who is to question him ？
It was the last film at the cinema ， which was to close next day.
After dinner they were to go to a movie.
was/ were to do 表示过去