Adverbial clauses of purpose are introduced by: "so that", "in order that", and "that" alone.
The auxiliaries may/might, can/could, will/would, shall/should are used as a rule in all clause of purpose.
May, can, shall, will are used when the main verb is in the present tense; could, might, should, would are used when the main verb is in the past tense.
Ex: I'm speaking clearly so that everybody here will understand me.
I stepped outside so that he could go in.
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