文档介绍：Abstract Contcmpomrily,advertisements have entered our modern 1ire without expectation and affected people’S attitudesand values are two subdivisions ofads due mercial ads and public serviceads (PSAs forshort).Lots ofattention ispaid totheresearches oftheformer,and little concern athome and abroad isconducted ’S more,researches ale primarily carried out with plenty of approaches from。aesthetics,psychology, linguistics,and concem吾of these studies are laid 011verbal level, conducting thefeatures on thelexical,grammatical,stylistic,rhetoric levels,etc. Nevertheless,in theage ofglobalization,these cannot explain thede印meaning hidden ,from CDA,a new angle,this thesisismade toimplement a more thorough analysis ofPSAs. This thesis holds thatPSAs,just likeany other discourses,are never all instrument delivering information in an indifferent way,but witllideology involved ,this study aims first to provide atheoreticalbackground and methodology fortheanalysis ofideologies inPSAs frommodality,personal system, andtransitivity,and conduct theusage characteristics oftheabove , combined withquantity andquality methods,this thesisadhibitsthemethodology to fi衄PSA discoursesselected atrandom toinspect how theyconvey ideology viathe application order toconduct thestudy,this thesishastorender the anSWer tothequestions asfollows: (1)What isthedistribution ofmodality,personal system andtransitivity inPSA discourses? (2)How isthefunction ofpublic serviceadvertising towards target audience realized intheform ofmodality,personal system andtransitivity? (3)What istherelationship between language,ideology and power inPSA discourses? Firstofall,this thesisanalyzes the distribution ofmodality,personal system and transitivity inPSAs from the macro perspective,finding that asformodality, Modalization ismore widely applied inPSAs thanModulation;as forpersonal system,the percentage ofthefirstpersonal pr