Student or Learner
Could anybody tell me if the expressions "so ~ that...", "~ enough to...", "so ~ as to..." are interchangeable one another? If not, in what cases?
I kept drinking coffee so as to stay awake.
Both sentences have an adverbial modifier of purpose. In the first sentence it is expressed by a clause, in the second - by an infinitive phrase.
As for 'enough to', I'm afraid, it's different. It may suggest a relation of consequence or comparison.