principal instrument principal instruments principal interest principal international principal investigator principal investigators principal investment principal investments principal issue principal issues principal language principal legal principal legislation principal level principal lewis principal madison principal market principal markets principal may principal member principal members principal method principal methods principal mission principal mode principal must principal object principal objective principal objectives principal observations principal occupation principal of a school principal of the college principal of the school principal office principal officer principal officers principal offices principal one principal ones principal organ principal organs principal organs of the united principal owner principal part principal partner principal partners principal parts principal payments principal photography principal photography began principal place principal place of business principal players principal point principal points principal policy principal political principal portion principal position principal private principal problem principal problems principal product principal production principal products principal provisions principal purpose principal question principal reason principal reasons principal recipient principal recipients principal recommendations principal repayment principal representative principal research principal researcher principal residence principal responsibilities principal responsibility principal results principal reynolds principal risk principal risks principal river principal rivers principal role principal roles principal root principal route principal said principal says principal scientific principal scientist principal secretary principal sent principal settlement principal shareholder