so/so that/that/in order that

它们在意义和功能上是没有区别的。但是在语体上却是有区别的。使用它们，是一个“把恰当的词用到恰当的地方”的问题。so that 常用于正式语体，尤其是科技语体中：

2. Some supplies of water must be treated so that they can be used. 某些水源必须预先加以处理，才能使用。

3. I am putting some oil on the hinge so that it will not squeak. 我在折页上上点油，以便它不再发出吱吱声。

so 用于不太正式的语体中, 故在科技语体中比较罕见:

1. He's getting a new car so he can impress his mother-in-law. (CGEL) 他打算买一辆新车，想给岳母一个好印象。

我会给你看，让你看清它是怎么做成的。

A. S. Hornby 之所以批评 Let the dog loose so that it can have a run. 这句话, 是因为它不口语化, 不符合说话的情景。他说, 他对妻子总是说: “Let it loose, so it can have a run.” (把狗放开, 让它跑一跑。)

that 显得异常地正式,有的语言学家认为它是古体,因此用得较罕见:

1. They have died that liberty might live. 他们死了，以求自由能够存在。

2. I'm only too anxious to get it done that I may be back in Ireland. (Yeats) 我急于把这件事干完，以便回到爱尔兰去。

3. The jury and witnesses were removed from the court that they might not hear the arguments of the lawyers. (CGEL)
   陪审团和证人退出了法庭，以便不听律师们的辩论。

in order that 用于相当正式的语体中, 表示经过精心策划的目的, 有时可与 so that 互换:

1. Let us spend a few moments in silence in order that (so that) we remember those who died to preserve our freedom.

让我们默哀片刻，以缅怀那些为维护自由而牺牲的人们。

2. In order that work can be done, in scientific sense, a force must move an object through some distance.

从科学意义上讲,为了做功,力必须推动物体通过一定的距离。