表示按计划发生的动作时，两者可互换。
我们明天就要搬到新房子里去了。We are moving to a new flat tomorrow
我们明天就要搬到新房子里去了。We are going to move to a new flat tomorrow
表示由于客观因素而产生的将来动作或状态时，用 be going to, 结构，不用 be +动词的- ing 形式。
如果你爬树的话，你会摔下来的。You are going to fall if you climb that tree
当心！你会把那张椅子弄坏的。Be careful, You are going to break that chair
不可说 Be careful, You are breaking that chair
be +动词不定式
表示按计划或安排将要发生的动作
这条公路将在五月份通车。The highway is to be open to traffic in May
我是不是要接管他的工作？Am I to take over his work ？
用于条件句中强调按计划或安排将要发生的动作
如果我们乘坐五点的火车的话，那我们现在就得出发。If we are to take the five o'clock train, we must leave now
表示命令或吩咐等。否定形式常表示“禁止”或“不许”。
你必须在10点前回来。You are to be back before ten p m
晚上你不能单独出去。You are not to go out alone at night
“ be going to +动词原形”侧重说话人个人的意图和打算，
“ be +动词不定式”侧重受别人的指示或安排要做的事。
我将尽力把这篇文章写好。I'm going to try my best to write this article well
我要在这儿一直等到他们抵达吗？Am I to wait here till their arrival？
表示由于客观因素或不受人控制的将要发生的动作时，只用“ be going to +动词原形”，不用“ be +动词不定式”。
天要下雨了。it 's going to rain
不说 it 's to rain
雷切尔要晕倒了。Rachel is going to faint
一般现在时表示将来时间的动作或状态 表示由于日历或时刻表的规定而固定不变的或比较不易变更的将来时间发生的动作。
明天是星期五。Tomorrow is Friday
下一班开往巴黎的火车几点出发？What time does the next train leave for Paris？
在时间状语从句或条件状语从句中，用一般现在时表示将来时间的动作或状态。
我看完这本书就给你。I'll give the book to you after I finish it
如果他到了，我们就到火车站去接他。If he arrives we must go and meet him at the railway station
在 hope suppose 等后面的宾语从句中常用一般现在时表示将来动作或状态。
我希望他一切都好。I hope all is well with him
我们明天还是去远足吧。Suppose we go hiking tomorrow
一般过去将来时是由“ should +动词原形， would +动词原形”构成的。
昨天他问我什么时候动身去巴黎。He asked me yesterday when I should leave for Paris
他们想知道怎样才能早一点儿完成家庭作业。They wanted to know how they would finish the homework earlier
一般过去将来时间的出发点是过去，即从过去某一时刻看以后要发生的动作和状态。
一般过去将来时常用于间接引语中
他说他们将安排一个晚会。He said they would arrange a party
我问他是否来帮我修电视机。I asked if he would come and fix my TV set
一般过去将来时可用来表示非真实的动作或状态
如果我有机会出国学习的话，我就会去剑桥大学。If I had a chance to study abroad, I would study at Cambridge University
今晚他能和我一起去看电影就好了。I wish he would go with me to the cinema tonight
was going to +动词原形， were going to +动词原形
他说他退休后要住在农村。He said that he was going to live in the country when he retired
他们认为天要下雨了。They thought it was going to rain
was +动词的- ing 形式， were +动词的- ing 形式
没人知道客人们是否要来。Nobody knew whether the guests were coming
我被告知火车几分钟后就要开了。I was told that the train was leaving in a few minutes
was +动词不定式， were +动词不定式
她说她放学后要打扫教室。She said she was to clean the classroom after school
据报道长江上将要再建一座大桥。it was reported that another bridge was to be built across the Yangtze River
“ was going to +动词原形， were going to +动词原形”或“ was +动词不定式完成式， were +动词不定式完成式”可表示未能实现的过去将来时间的动作。
上星期天我们本想去游览长城的，但却下雨了。Last Sunday we were going to visit the Great Wall but it rained
我是打算帮忙演出的，但前天我感冒了。I was to have helped with the performance but I got flu the day before
“ was about to do, were about to do ”表示说话的瞬间就会发生的动作。
我觉得有可怕的事要发生了。I felt something terrible was about to happen
即将; 临到was on the point of doing,
were on the point of doing
很高兴你来了。我正准备给你打电话，现在你省去我这个麻烦了。I'm glad you have come, I was on the point of calling you but you've saved me the trouble now
“ be about to do ”和“ be on the point of doing ”结构一般不与表示将来的时间状语连用，但后面可以接 when 引导的分句。
我正要动身天突然下雨了。I was about to start when it suddenly began to rain