目的状语从句的虚拟可以分为两类.
一、由 so that,in order that,引导的目的状语从句中,需要在从句的谓语语动词前加情态动词 can,may,could,might,前两个只用于现在时态,后两个既可以表示委婉的现在也可以表示过去,如：
* He works hard so that he can pass the exam.他努力学习,以便能够通过考试.
* He worked hard so that he could pass the exam.（当时）他刻苦地学习,以便能够通过考试.
* In order that he may pass the exam,he works hard.为了能够通过考试,他努力学习.
* He worked hard in order that he might pass the exam.为了能够通过考试,他当时努力地学习.
* He will come on time so that he could know everything from beginning.(委婉语气)
二、由 lest,for fear that 引导的目的状语从句,表示“以防、唯恐、免得”,之意,其谓语动词要用 should do,如：
* She tiptoed lest the guard should hear her.她踮起脚尖走路,以免守卫发现她.
* He ran away for fear that he should be seen.唯恐被人发现,他逃离了.
