A practical english grammar - Vyssaja skola 1978
Clauses of purpose and result
Sound symbols
The use of the infinitive to express purpose has already been mentioned (Chapter 11). There is a clause construction with similar meaning introduced by so that. The modals will, can, and may are usually used in clauses of purpose in the future; would, could, and might are frequently used in clauses referring to purpose in the past.
I’ll give you his telephone number, so that you won’t have to look it up. so that you can call him when you arrive, so that you may call him when you arrive.
He gave me his telephone number, so that I wouldn’t have to look it up. so that I could call him when I arrived, so that I might call him when I arrived.
Clauses of result are also expressed by so that; the context indicates the difference between result and purpose. Usually the verb in a result clause is expressed without the modals, so that it expresses real events rather than possible future ones. Informally that may be omitted from the phrase “so that.”
He gave me the number, so that I didn’t have to look it up.
There is also a construction consisting of so with an adjective or adverb and then a that-clause expressing a result of the condition expressed by the preceding word.
It is so early that no one has arrived yet.
This book is so long that I can’t finish it today.
She sings so beautifully that I can’t believe she has had no training.
The car was moving so fast that it could not stop at the intersection.
If a noun occurs along with an adjective in this structure, two patterns are available:
He is so excellent a teacher that many schools want to hire him.
He is such an excellent teacher that many schools want to hire him.
The pattern with such is much more frequent, since the pattern with so is considered extremely formal.