be going to/will

R.Quirk等人说过的一段话对于我们理解上面的问题,是很有帮助的:

“There are occasions where the choice of one construction(say will + infinitive) rather than another(say be going to + infinitive) has a scarcely perceptible effect on meaning. At the same time, there are differences of acceptability and usage which should not be ignored.”

[（“常常有这样一些情况：选择某一种结构（例如，will + 动词原形），而不选择另一种结构（比如，be going to + 动词原形），对于意义的影响几乎是觉察不出来的。然而在可接受性和惯用法上面却存在着一些不应忽视的差别。”）]

be going to 与 will 在惯用法方面差别主要反映在语体上。will 用于正式语体，而 be going to 主要用于口语体。所以，在正式的天气预报中常常采用含 will 的句式：

1. There will be rain. Fog will persist in these areas. (PEG) 有雨。一些地区仍然有雾。

2. There will be snow on high ground, and many mountain roads will be impassable. (CGEL) 高原有雪，许多山路将无法通行。

3. The day after tomorrow will be sunny. 后天天气晴朗。

而在口语体中则会将上面的 will 换成 is(are) going to。

1. They say it's going to be wet and windy. 据说,将有雨和风。

2. “Did you listen to the weather report on the radio?” “Yes, it's going to be dry and sunny for the next two days.” “你收听了电台的天气预报吗?” “是的，未来两天天气干

燥、晴朗。”

还应指出的另一个差别, 是 be going to 表示“经过事先考虑的意图或计划”, 而 will 表示“随时的意图”或“纯将来时意义”:

1. “There is somebody at the hall door.” “I'll go and open it.” “有人在大厅门外。”“我去开门。”（这里的 will 就不能用 am going to 来代替。）

2. It's hot in here, I'll open a window. 这儿很热，我去打开一扇窗户。

3. We're going to use the only means of transport left to us, the only ones the Trace can't detect. (J. K. Rowling, Harry Potter and the Deathly Hallows) 我们将用仅存的运输方法，唯一一种不会被探测的方法。(《哈利·波特与死亡圣徒》)

此外, be going to 表示即将发生的事或不久将来发生的事, 而 will 除此之外也可以表示很遥远的事:

1. I am going to sell this old car, and buy a new one. 我打算把旧车卖掉，买辆新车。

2. Help! I'm going to fall! 救命！我要掉下去了！