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sb to do sth 单独不能表示什么,必须在前面加上动词,才能算是固定短语的用法.比如 make sb to do sth,使某人做某事；ask sb to do sth,要求/命令某人去做某事.
你说的表示将来时的 应该是“be to do”这个结构吧.一般说来两种语法意义,一是系动词be+动词不定式做表语,二是be to作为固定用法,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等同.如：
The problem is to find a solution.问题是找到一个解决方法.
His plan is to clean the room.他的计划是打扫房间.
My wish is to be a doctor.我的希望是做一个医生.
二、be to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).
1.表示“将”、“计划”、“安排”.(意思接近于be going to)如：
He is to have a holiday.
Their daughter is to get married soon.
The committee is to meet today.
After dinner they were to go to a movie.
was/ were to do表示过去曾经计划要做的事,或者过去应当做的事,而且从现在的角度来看已经实现了.如：
I felt nervous because I was soon to leave home for the first time.
The expedition was to start in a week’s time.
was/ were to have done,表示“本打算”、“本计划”或“本应当”做的事而没有做成或没有发生.如:
I was to have seen him last Wednesday,but he didn’t come.
We were to have been married last year.
2.表示“义务”、“应该” .(意思接近于should,must,ought to,have to)如：
No one is to leave the building.谁也不得离开这楼房.
You are not to smoke in this room.=You are not supposed to smoke in this room.
You are to be back by 10 o’clock.你必须十点以前回来.
3.表示可能性,相当于can,may如:
Such books are to be found in the library.这样的书在图书馆里就能找到.
Not a single sound was to be heard.一点儿声音也听不到.
Not a soul was to be seen.看不到一个人影.
5.表示“命运”,将来必然要发生的事,译作“注定……”.如：
The worst is still to come.
They said goodbye,little knowing they were never to meet again.
6.用于“if…were to do”,表示虚拟语气.如：
If it were to rain tomorrow,the sports meeting would be put off.如果明天下雨,运动会就会延期.
sb to do sth 单独不能表示什么,必须在前面加上动词,才能算是固定短语的用法.比如 make sb to do sth,使某人做某事；ask sb to do sth,要求/命令某人去做某事.
你说的表示将来时的 应该是“be to do”这个结构吧.一般说来两种语法意义,一是系动词be+动词不定式做表语,二是be to作为固定用法,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等同.如：
The problem is to find a solution.问题是找到一个解决方法.
His plan is to clean the room.他的计划是打扫房间.
My wish is to be a doctor.我的希望是做一个医生.
二、be to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).
1.表示“将”、“计划”、“安排”.(意思接近于be going to)如：
He is to have a holiday.
Their daughter is to get married soon.
The committee is to meet today.
After dinner they were to go to a movie.
was/ were to do表示过去曾经计划要做的事,或者过去应当做的事,而且从现在的角度来看已经实现了.如：
I felt nervous because I was soon to leave home for the first time.
The expedition was to start in a week’s time.
was/ were to have done,表示“本打算”、“本计划”或“本应当”做的事而没有做成或没有发生.如:
I was to have seen him last Wednesday,but he didn’t come.
We were to have been married last year.
2.表示“义务”、“应该” .(意思接近于should,must,ought to,have to)如：
No one is to leave the building.谁也不得离开这楼房.
You are not to smoke in this room.=You are not supposed to smoke in this room.
You are to be back by 10 o’clock.你必须十点以前回来.
3.表示可能性,相当于can,may如:
Such books are to be found in the library.这样的书在图书馆里就能找到.
Not a single sound was to be heard.一点儿声音也听不到.
Not a soul was to be seen.看不到一个人影.
5.表示“命运”,将来必然要发生的事,译作“注定……”.如：
The worst is still to come.
They said goodbye,little knowing they were never to meet again.
6.用于“if…were to do”,表示虚拟语气.如：
If it were to rain tomorrow,the sports meeting would be put off.如果明天下雨,运动会就会延期.