father ▁policy ▁or ▁grand father ing ) ▁is ▁a ▁provision ▁in ▁which ▁an ▁old ▁rule ▁continues ▁to ▁apply ▁to ▁some ▁existing ▁situations ▁while ▁a ▁new ▁rule ▁will ▁apply ▁to ▁all ▁future ▁cases . ▁Those ▁ex empt ▁from ▁the ▁new ▁rule ▁are ▁said ▁to ▁have ▁grand father ▁rights ▁or ▁acquired ▁rights , ▁or ▁to ▁have ▁been ▁grand father ed ▁in . ▁Fre qu ently , ▁the ▁exem ption ▁is ▁limited ; ▁it ▁may ▁extend ▁for ▁a ▁set ▁time , ▁or ▁it ▁may ▁be ▁lost ▁under ▁certain ▁circumstances . ▁For ▁example , ▁a ▁grand father ed ▁power ▁plant ▁might ▁be ▁ex empt ▁from ▁new , ▁more ▁restrict ive ▁poll ution ▁laws , ▁but ▁the ▁exception ▁may ▁be ▁rev oked ▁and ▁the ▁new ▁rules ▁would ▁apply ▁if ▁the ▁plant ▁were ▁expanded . ▁O ften , ▁such ▁a ▁provision ▁is ▁used ▁as ▁a ▁comprom ise ▁or ▁out ▁of ▁practical ity , ▁to ▁allow ▁new ▁rules ▁to ▁be ▁en act ed ▁without ▁ups et ting ▁a ▁well - est ab lished ▁log ist ical ▁or ▁political ▁situation . ▁This ▁extends ▁the ▁idea ▁of ▁a ▁rule ▁not ▁being ▁retro act ively ▁applied . ▁ ▁The ▁term ▁origin ated ▁in ▁late ▁nin ete enth - century ▁legisl ation ▁and ▁constitution al ▁am end ments ▁passed ▁by ▁a ▁number ▁of ▁U . S . ▁Southern ▁states , ▁which ▁created ▁new ▁requirements ▁for ▁liter acy ▁tests , ▁payment ▁of ▁poll ▁tax es , ▁and / or ▁res iden cy ▁and ▁property ▁restrictions ▁to ▁register ▁to ▁vote . ▁States ▁in ▁some ▁cases ▁ex