A clause which is used to tell you about the purpose of the verb in the main clause is called adverb clause of purpose.
Adverb clauses of purpose are introduced by the subordinating conjunctions that, so that, in order that, in order to and lest. Moreover, these expressions are usually followed by modal auxiliary verbs such as will, can, may, could or might.
Adverb Clause of Purpose Examples:
- They practice hard so that they might qualify for the final. (Here in this sentence the adverb clause “so that they might qualify for the final” is the purpose for which they practice hard).
- She was so tired (that) she couldn’t think straight. (Here is this sentence the adverb clause “that she couldn’t think straight” is the purpose of her tiredness)
- We play well so that we may win.
- Play carefully lest you should lose.
- He gripped his brother’s arm lest he be trampled by the mob.
- We left early in order that guests might reach home before us.
- I learn English in order to increase the standard of living.
IMPORTANT:
1) So that is more common than in order that.
2) In an informal style that can be dropped after so; this is very common in American English.
- I have come early so that I can meet you. OR
- I have come early so I can meet you.
3) In some sentences you can drop the modal auxiliary verb when it is followed by so that.
- We are going to leave early so that we (will) reach by three o’clock.
4) Lest means in order to prevent something from happening or that…not, and, therefore, it will be wrong to add another not in a sentence.
- Bring all documents to attest to its truth lest they should doubt your story. OR
- Bring all documents to attest to its truth lest they doubt your story.
- (NOT Bring all documents to attest to its truth lest they don’t doubt your story.