《语言学教程》Language：Languageissystemofarbitraryvocalsymbolsusedforhumancommunication.designfeaturesoflanguage：“Designfeatures”hererefertothedefiningpropertiesofhumanlanguagethattellthedifferencebetweenhumanlanguageandanysystemofanimalcommunication.Theyarearbitrariness,duality,productivity,displacement,culturaltransmission.arbitrariness：By“arbitrariness”,wemeanthereisnologicalconnectionbetweenmeaningsandsounds.duality：Linguistsrefer“duality”(ofstructure)tothefactthatinalllanguagessofarinvestigated,onefindstwolevelsofstructureorpatterning.productivity：Productivityreferstotheabilitytotheabilitytoconstructandunderstandanindefinitelylargenumberofsentencesinone’snativelanguage,includingthosethathasneverheardbefore,butthatareappropriatetothespeakingsituation.displacement：“Displacement”,asoneofthedesignfeaturesofthehumanlanguage,referstothefactthatonecantalkaboutthingsthatarenotpresent,aseasilyashedoesthingspresent.linguistics：“Linguistics”isthescientificstudyoflanguage.Itstudiesnotjustonelanguageofanyonesociety,butthelanguageofallhumanbeings.Alinguist,though,doesnothavetoknowandusealargenumberoflanguages,buttoinvestigatehoweachlanguageisconstructed.Heisalsoconcernedwithhowalanguagevariesfromdialecttodialect,fromclasstoclass,howitchangesfromcenturytocentury,howchildrenacquiretheirmothertongue,andperhapshowapersonlearnsorshouldlearnaforeignlanguage.Inshort,linguisticsstudiesthegeneralprincipleswhereuponallhumanlanguagesareconstructedandoperateassystemsofcommunicationintheirsocietiesorcommunitiesmajorbranchesoflinguistics：Thestudyoflanguageasawholeisoftencalledgenerallinguistics.Butalinguistsometimesisabletodealwithonlyoneaspectoflanguageatatime,thustheariseofvariousbranches:phonetics,phonology,morphology,syntax,semantics,sociolinguistics,appliedlinguistics,pragmatics,psycholinguistics,lexicology,lexicography,etymology,etc.synchronicanddiachronicstudies：Thedescriptionofalanguageatsomepointoftime(asifitstoppeddeveloping)isasynchronystudy(synchrony).Thedescriptionofalang