主情从现是指:如果句子中有情态动词,那么情态动词后加一般现在时的动词,即动词原型。如:Ifyoufeelhungry,youshouldeatsomething.
主祈从现是指:如果主句是祈使句,从句用一般现在时。如:Pleaseletmeknowifhecomesback.
主将从现是指:在时间状语从句、条件状语从句和让步状语从句中,如果主句是一般将来时,从句用一般现在时替代一般将来时。如:WhenIgrowup,Iwillbeanurseandlookafterpatients/Iwanttobeanurseandlookafterpatients.