Philosophy Ethics thumb|right|200px|The title page of Principia Ethica. His influential work Principia Ethica is one of the main inspirations of the reaction against ethical naturalism (see ethical non-naturalism) and is partly responsible for the twentieth-century concern with meta-ethics. by Geoff Sayre-McCord.
PhilOSoPhY ethIcs tHuMb|RiGhT|200Px|the titLE page of pRinCiPia etHiCa. hiS inFluential worK PRinCipiA EthiCa is oNE of THe MaIn inSpirations oF THE rEaCtion againsT EthICal natuRaLiSM (SeE eTHIcAl nOn-NATUraLiSM) And is paRTLY REsPonsiblE For thE tWeNtIEth-ceNtury cOncERN WITh MetA-etHIcs. by Geoff SAyre-mccoRD.