without,otherwise,butfor,but引导的短语或句子有时相当于一个虚拟条件句.假设的情况并不以条件从句表示出来,而是暗含在上下文中,通过介词短语来表示.

　　使用到这些词组的句子中,虚拟语气的用法一般是：对现在的虚拟：would+do；对过去的虚拟：would(not)+havedone.

　　比如：Butforyourreasonableadvice,iwouldn'thavefininshedmypaperexcellently.WithoutbringinhimasthePM(projectmanager项目经理)ofourcompany,theimportantprogramwouldhavefailed.

　　Ishouldstudymorehard,otherwiseiwouldhavekepetwiththemostoutstandingsutdentinmyclassinlastexam.Yourmotherwouldgowithyou,butshehastotakecareofyourelderbrother