Are "so" and "so that" interchangeable?
A book suggests that we should not interchange "so" and "so that". "So" means "therefore", and "so that" means "in order that". However, it seems to me that in many cases they don't actually have a difference. For example:
Alice got up at 5:00 A.M., so that she could drive her son to school.
If I substitute "so that" with "so", this sentence presents the exact same causal relation to me:
Alice got up at 5:00 A.M., so she could drive her son to school.
I must have missed something here, since English is my second language. Could somebody explain the difference?
If you are wondering about the difference between the two sentences, the first states Alice's reason for waking up early, while the second implies that she was successful in her intention.
This is not a distinction always observed by native speakers.
It is confusing, because "so" (when used as a conjunction) can mean "therefore" or can be an abbreviated form of "so that" (meaning "in order that.") In this way "so" has two distinct but similar meanings.
Subjectively I would say that using "so" in place of "so that" sounds a little informal and maybe a tiny bit childish, but is fine in conversational contexts.
They aren't interchangeable.
"so" is ambiguous, meaning both therefore and in order that, but "so that" isn't. Every occurrence of "so that" can be replaced with "so" without losing meanings, but not vice versa. For instance,
You are a bachelor, so you are a man.
"so" means therefore in this context. It doesn't make sense replacing "so" with "so that", the latter of which means "in order that". You are a bachelor in order to be a man?
Note: If two words can only be replaced with each other in some cases, your example being one of them, but not all, are they really interchangeable?
According to AHD
so ... conj. ...
- With the purpose that: I stayed so I could see you.
the use of 'so' instead of 'so that' when used to mean 'with the purpose that' is acceptable. They have a usage note:
Many critics and grammarians have insisted that so must be followed by that in formal writing when used to introduce a clause giving the reason for or purpose of an action:
He stayed so that he could see the second feature.
But since many respected writers use so for so that in formal writing, it seems best to consider the issue one of stylistic preference:
The store stays open late so (or so that) people who work all day can buy groceries.
Both so and so that are acceptably used to introduce clauses that state a result or consequence:
The Bay Bridge was still closed, so (or so that) the drive from San Francisco to the Berkeley campus took an hour and a half.
So that means "with the result that", "with the aim that", "in order that".
It was overgrown with brambles, so that she had difficulty making any progress.
They whisper to each other so that no one else can hear.
So means "to such a great extent", "extremely", "very much".
As conjunction, it means "and for this reason", "therefore", "and then"; it is also used to introduce a question, or a concluding statement.
She looked so pretty.
She likes it so.
She is not so foolish as to believe that.
It was still painful, so I went to see a specialist.
So, what is her name?
So that is the reason.
So you are free.
You cannot replace so with so that without changing the meaning of the sentence, or without changing the rest of the sentence.