PREFATORYNOTEBYTHEAUTHOR
IfthisDiscourseappeartoolongtobereadatonce，itmaybedividedintosixParts：and，inthefirst，willbefoundvariousconsiderationstouchingtheSciences；inthesecond，theprincipalrulesoftheMethodwhichtheAuthorhasdiscovered，inthethird，certainoftherulesofMoralswhichhehasdeducedfromthisMethod；inthefourth，thereasoningsbywhichheestablishestheexistenceofGodandoftheHumanSoul，whicharethefoundationsofhisMetaphysic；inthefifth，theorderofthePhysicalquestionswhichhehasinvestigated，and，inparticular，theexplicationofthemotionoftheheartandofsomeotherdifficultiespertainingtoMedicine，asalsothedifferencebetweenthesoulofmanandthatofthebrutes；and，inthelast，whattheAuthorbelievestoberequiredinordertogreateradvancementintheinvestigationofNaturethanhasyetbeenmade，withthereasonsthathaveinducedhimtowrite。
PART1
Goodsenseis，ofallthingsamongmen，themostequallydistributed；foreveryonethinkshimselfsoabundantlyprovidedwithit，thatthoseevenwhoarethemostdifficulttosatisfyineverythingelse，donotusuallydesirealargermeasureofthisqualitythantheyalreadypossess。Andinthisitisnotlikelythatallaremistakentheconvictionisrathertobeheldastestifyingthatthepowerofjudgingarightandofdistinguishingtruthfromerror，whichisproperlywhatiscalledgoodsenseorreason，isbynatureequalinallmen；andthatthediversityofouropinions，consequently，doesnotarisefromsomebeingendowedwithalargershareofreasonthanothers，butsolelyfromthis，thatweconductourthoughtsalongdifferentways，anddonotfixourattentiononthesameobjects。
Fortobepossessedofavigorousmindisnotenough；theprimerequisiteisrightlytoapplyit。Thegreatestminds，astheyarecapableofthehighestexcellences，areopenlikewisetothegreatestaberrations；andthosewhotravelveryslowlymayyetmakefargreaterprogress，providedtheykeepalwaystothestraightroad，thanthosewho，whiletheyrun，forsakeit。
Formyself，Ihaveneverfanciedmymindtobeinanyrespectmoreperfectthanthoseofthegenerality；onthecontrary，IhaveoftenwishedthatI
wereequaltosomeothersinpromptitudeofthought，orinclearnessanddistinctnessofimagination，orinfullnessandreadinessofmemory。Andbesidesthese，Iknowofnootherqualitiesthatcontributetotheperfectionofthemind；forastothereasonorsense，inasmuchasitisthatalonewhichconstitutesusmen，anddistinguishesusfromthebrutes，Iamdisposedtobelievethatitistobefoundcompleteineachindividual；andonthispointtoadoptthecommonopinionofphilosophers，whosaythatthedifferenceofgreaterandlessholdsonlyamongtheaccidents，andnotamongtheformsornaturesofindividualsofthesamespecies。
Iwillnothesitate，however，toavowmybeliefthatithasbeenmysingulargoodfortunetohaveveryearlyinlifefalleninwithcertaintrackswhichhaveconductedmetoconsiderationsandmaxims，ofwhichI
haveformedamethodthatgivesmethemeans，asIthink，ofgraduallyaugmentingmyknowledge，andofraisingitbylittleandlittletothehighestpointwhichthemediocrityofmytalentsandthebriefdurationofmylifewillpermitmetoreach。ForIhavealreadyreapedfromitsuchfruitsthat，althoughIhavebeenaccustomedtothinklowlyenoughofmyself，andalthoughwhenIlookwiththeeyeofaphilosopheratthevariedcoursesandpursuitsofmankindatlarge，Ifindscarcelyonewhichdoesnotappearinvainanduseless，IneverthelessderivethehighestsatisfactionfromtheprogressIconceivemyselftohavealreadymadeinthesearchaftertruth，andcannothelpentertainingsuchexpectationsofthefutureastobelievethatif，amongtheoccupationsofmenasmen，thereisanyonereallyexcellentandimportant，itisthatwhichIhavechosen。
Afterall，itispossibleImaybemistaken；anditisbutalittlecopperandglass，perhaps，thatItakeforgoldanddiamonds。Iknowhowveryliablewearetodelusioninwhatrelatestoourselves，andalsohowmuchthejudgmentsofourfriendsaretobesuspectedwhengiveninourfavor。ButIshallendeavorinthisdiscoursetodescribethepathsI
havefollowed，andtodelineatemylifeasinapicture，inorderthateachonemayalsobeabletojudgeofthemforhimself，andthatinthegeneralopinionentertainedofthem，asgatheredfromcurrentreport，I
myselfmayhaveanewhelptowardsinstructiontobeaddedtothoseIhavebeeninthehabitofemploying。
Mypresentdesign，then，isnottoteachthemethodwhicheachoughttofollowfortherightconductofhisreason，butsolelytodescribethewayinwhichIhaveendeavoredtoconductmyown。Theywhosetthemselvestogivepreceptsmustofcourseregardthemselvesaspossessedofgreaterskillthanthosetowhomtheyprescribe；andiftheyerrintheslightestparticular，theysubjectthemselvestocensure。Butasthistractisputforthmerelyasahistory，or，ifyouwill，asatale，inwhich，amidsomeexamplesworthyofimitation，therewillbefound，perhaps，asmanymorewhichitwereadvisablenottofollow，Ihopeitwillproveusefultosomewithoutbeinghurtfultoany，andthatmyopennesswillfindsomefavorwithall。
Frommychildhood，Ihavebeenfamiliarwithletters；andasIwasgiventobelievethatbytheirhelpaclearandcertainknowledgeofallthatisusefulinlifemightbeacquired，Iwasardentlydesirousofinstruction。
ButassoonasIhadfinishedtheentirecourseofstudy，atthecloseofwhichitiscustomarytobeadmittedintotheorderofthelearned，I
completelychangedmyopinion。ForIfoundmyselfinvolvedinsomanydoubtsanderrors，thatIwasconvincedIhadadvancednofartherinallmyattemptsatlearning，thanthediscoveryateveryturnofmyownignorance。AndyetIwasstudyinginoneofthemostcelebratedschoolsinEurope，inwhichIthoughttheremustbelearnedmen，ifsuchwereanywheretobefound。Ihadbeentaughtallthatotherslearnedthere；
andnotcontentedwiththesciencesactuallytaughtus，Ihad，inaddition，readallthebooksthathadfallenintomyhands，treatingofsuchbranchesasareesteemedthemostcuriousandrare。Iknewthejudgmentwhichothershadformedofme；andIdidnotfindthatIwasconsideredinferiortomyfellows，althoughtherewereamongthemsomewhowerealreadymarkedouttofilltheplacesofourinstructors。And，infine，ourageappearedtomeasflourishing，andasfertileinpowerfulmindsasanyprecedingone。Iwasthusledtotakethelibertyofjudgingofallothermenbymyself，andofconcludingthattherewasnoscienceinexistencethatwasofsuchanatureasIhadpreviouslybeengiventobelieve。
Istillcontinued，however，toholdinesteemthestudiesoftheschools。
Iwasawarethatthelanguagestaughtinthemarenecessarytotheunderstandingofthewritingsoftheancients；thatthegraceoffablestirsthemind；thatthememorabledeedsofhistoryelevateit；and，ifreadwithdiscretion，aidinformingthejudgment；thattheperusalofallexcellentbooksis，asitwere，tointerviewwiththenoblestmenofpastages，whohavewrittenthem，andevenastudiedinterview，inwhicharediscoveredtousonlytheirchoicestthoughts；thateloquencehasincomparableforceandbeauty；thatpoesyhasitsravishinggracesanddelights；thatinthemathematicstherearemanyrefineddiscoverieseminentlysuitedtogratifytheinquisitive，aswellasfurtheralltheartsanlessenthelabourofman；thatnumeroushighlyusefulpreceptsandexhortationstovirtuearecontainedintreatisesonmorals；thattheologypointsoutthepathtoheaven；thatphilosophyaffordsthemeansofdiscoursingwithanappearanceoftruthonallmatters，andcommandstheadmirationofthemoresimple；thatjurisprudence，medicine，andtheothersciences，securefortheircultivatorshonorsandriches；and，infine，thatitisusefultobestowsomeattentionuponall，evenuponthoseaboundingthemostinsuperstitionanderror，thatwemaybeinapositiontodeterminetheirrealvalue，andguardagainstbeingdeceived。
ButIbelievedthatIhadalreadygivensufficienttimetolanguages，andlikewisetothereadingofthewritingsoftheancients，totheirhistoriesandfables。Fortoholdconversewiththoseofotheragesandtotravel，arealmostthesamething。Itisusefultoknowsomethingofthemannersofdifferentnations，thatwemaybeenabledtoformamorecorrectjudgmentregardingourown，andbepreventedfromthinkingthateverythingcontrarytoourcustomsisridiculousandirrational，aconclusionusuallycometobythosewhoseexperiencehasbeenlimitedtotheirowncountry。Ontheotherhand，whentoomuchtimeisoccupiedintraveling，webecomestrangerstoournativecountry；andtheovercuriousinthecustomsofthepastaregenerallyignorantofthoseofthepresent。Besides，fictitiousnarrativesleadustoimaginethepossibilityofmanyeventsthatareimpossible；andeventhemostfaithfulhistories，iftheydonotwhollymisrepresentmatters，orexaggeratetheirimportancetorendertheaccountofthemmoreworthyofperusal，omit，atleast，almostalwaysthemeanestandleaststrikingoftheattendantcircumstances；henceithappensthattheremainderdoesnotrepresentthetruth，andthatsuchasregulatetheirconductbyexamplesdrawnfromthissource，areapttofallintotheextravagancesoftheknight—errantsofromance，andtoentertainprojectsthatexceedtheirpowers。
Iesteemedeloquencehighly，andwasinraptureswithpoesy；butIthoughtthatbothweregiftsofnatureratherthanfruitsofstudy。Thoseinwhomthefacultyofreasonispredominant，andwhomostskillfullydisposetheirthoughtswithaviewtorenderthemclearandintelligible，arealwaysthebestabletopersuadeothersofthetruthofwhattheylaydown，thoughtheyshouldspeakonlyinthelanguageofLowerBrittany，andbewhollyignorantoftherulesofrhetoric；andthosewhosemindsarestoredwiththemostagreeablefancies，andwhocangiveexpressiontothemwiththegreatestembellishmentandharmony，arestillthebestpoets，thoughunacquaintedwiththeartofpoetry。
Iwasespeciallydelightedwiththemathematics，onaccountofthecertitudeandevidenceoftheirreasonings；butIhadnotasyetapreciseknowledgeoftheirtrueuse；andthinkingthattheybutcontributedtotheadvancementofthemechanicalarts，Iwasastonishedthatfoundations，sostrongandsolid，shouldhavehadnoloftiersuperstructurerearedonthem。Ontheotherhand，Icomparedthedisquisitionsoftheancientmoraliststoverytoweringandmagnificentpalaceswithnobetterfoundationthansandandmud：theylaudthevirtuesveryhighly，andexhibitthemasestimablefaraboveanythingonearth；
buttheygiveusnoadequatecriterionofvirtue，andfrequentlythatwhichtheydesignatewithsofineanameisbutapathy，orpride，ordespair，orparricide。
Ireveredourtheology，andaspiredasmuchasanyonetoreachheaven：
butbeinggivenassuredlytounderstandthatthewayisnotlessopentothemostignorantthantothemostlearned，andthattherevealedtruthswhichleadtoheavenareaboveourcomprehension，Ididnotpresumetosubjectthemtotheimpotencyofmyreason；andIthoughtthatinordercompetentlytoundertaketheirexamination，therewasneedofsomespecialhelpfromheaven，andofbeingmorethanman。
OfphilosophyIwillsaynothing，exceptthatwhenIsawthatithadbeencultivatedformanyagesbythemostdistinguishedmen，andthatyetthereisnotasinglematterwithinitsspherewhichisnotstillindispute，andnothing，therefore，whichisabovedoubt，Ididnotpresumetoanticipatethatmysuccesswouldbegreaterinitthanthatofothers；andfurther，whenIconsideredthenumberofconflictingopinionstouchingasinglematterthatmaybeupheldbylearnedmen，whiletherecanbebutonetrue，Ireckonedaswell—nighfalseallthatwasonlyprobable。
Astotheothersciences，inasmuchastheseborrowtheirprinciplesfromphilosophy，Ijudgedthatnosolidsuperstructurescouldberearedonfoundationssoinfirm；andneitherthehonornorthegainheldoutbythemwassufficienttodeterminemetotheircultivation：forIwasnot，thankHeaven，inaconditionwhichcompelledmetomakemerchandiseofscienceforthebetteringofmyfortune；andthoughImightnotprofesstoscorngloryasacynic，IyetmadeveryslightaccountofthathonorwhichI
hopedtoacquireonlythroughfictitioustitles。And，infine，offalsesciencesIthoughtIknewtheworthsufficientlytoescapebeingdeceivedbytheprofessionsofanalchemist，thepredictionsofanastrologer，theimposturesofamagician，orbytheartificesandboastingofanyofthosewhoprofesstoknowthingsofwhichtheyareignorant。
Forthesereasons，assoonasmyagepermittedmetopassfromunderthecontrolofmyinstructors，Ientireyabandonedthestudyofletters，andresolvednolongertoseekanyothersciencethantheknowledgeofmyself，orofthegreatbookoftheworld。Ispenttheremainderofmyyouthintraveling，invisitingcourtsandarmies，inholdingintercoursewithmenofdifferentdispositionsandranks，incollectingvariedexperience，inprovingmyselfinthedifferentsituationsintowhichfortunethrewme，and，aboveall，inmakingsuchreflectiononthematterofmyexperienceastosecuremyimprovement。ForitoccurredtomethatIshouldfindmuchmoretruthinthereasoningsofeachindividualwithreferencetotheaffairsinwhichheispersonallyinterested，andtheissueofwhichmustpresentlypunishhimifhehasjudgedamiss，thaninthoseconductedbyamanoflettersinhisstudy，regardingspeculativemattersthatareofnopracticalmoment，andfollowedbynoconsequencestohimself，farther，perhaps，thanthattheyfosterhisvanitythebetterthemoreremotetheyarefromcommonsense；requiring，astheymustinthiscase，theexerciseofgreateringenuityandarttorenderthemprobable。Inaddition，Ihadalwaysamostearnestdesiretoknowhowtodistinguishthetruefromthefalse，inorderthatImightbeableclearlytodiscriminatetherightpathinlife，andproceedinitwithconfidence。
Itistruethat，whilebusiedonlyinconsideringthemannersofothermen，Ifoundhere，too，scarceanygroundforsettledconviction，andremarkedhardlylesscontradictionamongthemthanintheopinionsofthephilosophers。SothatthegreatestadvantageIderivedfromthestudyconsistedinthis，that，observingmanythingswhich，howeverextravagantandridiculoustoourapprehension，areyetbycommonconsentreceivedandapprovedbyothergreatnations，IlearnedtoentertaintoodecidedabeliefinregardtonothingofthetruthofwhichIhadbeenpersuadedmerelybyexampleandcustom；andthusIgraduallyextricatedmyselffrommanyerrorspowerfulenoughtodarkenournaturalintelligence，andincapacitateusingreatmeasurefromlisteningtoreason。ButafterIhadbeenoccupiedseveralyearsinthusstudyingthebookoftheworld，andinessayingtogathersomeexperience，Iatlengthresolvedtomakemyselfanobjectofstudy，andtoemployallthepowersofmymindinchoosingthepathsIoughttofollow，anundertakingwhichwasaccompaniedwithgreatersuccessthanitwouldhavebeenhadIneverquittedmycountryormybooks。
PARTII
IwastheninGermany，attractedthitherbythewarsinthatcountry，whichhavenotyetbeenbroughttoatermination；andasIwasreturningtothearmyfromthecoronationoftheemperor，thesettinginofwinterarrestedmeinalocalitywhere，asIfoundnosocietytointerestme，andwasbesidesfortunatelyundisturbedbyanycaresorpassions，Iremainedthewholedayinseclusion，withfullopportunitytooccupymyattentionwithmyownthoughts。Oftheseoneoftheveryfirstthatoccurredtomewas，thatthereisseldomsomuchperfectioninworkscomposedofmanyseparateparts，uponwhichdifferenthandshadbeenemployed，asinthosecompletedbyasinglemaster。Thusitisobservablethatthebuildingswhichasinglearchitecthasplannedandexecuted，aregenerallymoreelegantandcommodiousthanthosewhichseveralhaveattemptedtoimprove，bymakingoldwallsserveforpurposesforwhichtheywerenotoriginallybuilt。Thusalso，thoseancientcitieswhich，frombeingatfirstonlyvillages，havebecome，incourseoftime，largetowns，areusuallybutilllaidoutcomparedwiththeregularityconstructedtownswhichaprofessionalarchitecthasfreelyplannedonanopenplain；sothatalthoughtheseveralbuildingsoftheformermayoftenequalorsurpassinbeautythoseofthelatter，yetwhenoneobservestheirindiscriminatejuxtaposition，therealargeoneandhereasmall，andtheconsequentcrookednessandirregularityofthestreets，oneisdisposedtoallegethatchanceratherthananyhumanwillguidedbyreasonmusthaveledtosuchanarrangement。Andifweconsiderthatneverthelesstherehavebeenatalltimescertainofficerswhosedutyitwastoseethatprivatebuildingscontributedtopublicornament，thedifficultyofreachinghighperfectionwithbutthematerialsofotherstooperateon，willbereadilyacknowledged。InthesamewayIfanciedthatthosenationswhich，startingfromasemi—barbarousstateandadvancingtocivilizationbyslowdegrees，havehadtheirlawssuccessivelydetermined，and，asitwere，forceduponthemsimplybyexperienceofthehurtfulnessofparticularcrimesanddisputes，wouldbythisprocesscometobepossessedoflessperfectinstitutionsthanthosewhich，fromthecommencementoftheirassociationascommunities，havefollowedtheappointmentsofsomewiselegislator。Itisthusquitecertainthattheconstitutionofthetruereligion，theordinancesofwhicharederivedfromGod，mustbeincomparablysuperiortothatofeveryother。And，tospeakofhumanaffairs，Ibelievethatthepre—eminenceofSpartawasduenottothegoodnessofeachofitslawsinparticular，formanyofthesewereverystrange，andevenopposedtogoodmorals，buttothecircumstancethat，originatedbyasingleindividual，theyalltendedtoasingleend。InthesamewayIthoughtthatthesciencescontainedinbooks（suchofthematleastasaremadeupofprobablereasonings，withoutdemonstrations），composedastheyareoftheopinionsofmanydifferentindividualsmassedtogether，arefartherremovedfromtruththanthesimpleinferenceswhichamanofgoodsenseusinghisnaturalandunprejudicedjudgmentdrawsrespectingthemattersofhisexperience。Andbecausewehavealltopassthroughastateofinfancytomanhood，andhavebeenofnecessity，foralengthoftime，governedbyourdesiresandpreceptors（whosedictateswerefrequentlyconflicting，whileneitherperhapsalwayscounseledusforthebest），I
fartherconcludedthatitisalmostimpossiblethatourjudgmentscanbesocorrectorsolidastheywouldhavebeen，hadourreasonbeenmaturefromthemomentofourbirth，andhadwealwaysbeenguidedbyitalone。
Itistrue，however，thatitisnotcustomarytopulldownallthehousesofatownwiththesingledesignofrebuildingthemdifferently，andtherebyrenderingthestreetsmorehandsome；butitoftenhappensthataprivateindividualtakesdownhisownwiththeviewoferectingitanew，andthatpeopleareevensometimesconstrainedtothiswhentheirhousesareindangeroffallingfromage，orwhenthefoundationsareinsecure。
Withthisbeforemebywayofexample，Iwaspersuadedthatitwouldindeedbepreposterousforaprivateindividualtothinkofreformingastatebyfundamentallychangingitthroughout，andoverturningitinordertosetitupamended；andthesameIthoughtwastrueofanysimilarprojectforreformingthebodyofthesciences，ortheorderofteachingthemestablishedintheschools：butasfortheopinionswhichuptothattimeIhadembraced，IthoughtthatIcouldnotdobetterthanresolveatoncetosweepthemwhollyaway，thatImightafterwardsbeinapositiontoadmiteitherothersmorecorrect，orevenperhapsthesamewhentheyhadundergonethescrutinyofreason。IfirmlybelievedthatinthiswayI
shouldmuchbettersucceedintheconductofmylife，thanifIbuiltonlyuponoldfoundations，andleaneduponprincipleswhich，inmyyouth，Ihadtakenupontrust。ForalthoughIrecognizedvariousdifficultiesinthisundertaking，thesewerenot，however，withoutremedy，noroncetobecomparedwithsuchasattendtheslightestreformationinpublicaffairs。
Largebodies，ifonceoverthrown，arewithgreatdifficultysetupagain，orevenkepterectwhenonceseriouslyshaken，andthefallofsuchisalwaysdisastrous。Thenifthereareanyimperfectionsintheconstitutionsofstates（andthatmanysuchexistthediversityofconstitutionsisalonesufficienttoassureus），customhaswithoutdoubtmateriallysmoothedtheirinconveniences，andhasevenmanagedtosteeraltogetherclearof，orinsensiblycorrectedanumberwhichsagacitycouldnothaveprovidedagainstwithequaleffect；and，infine，thedefectsarealmostalwaysmoretolerablethanthechangenecessaryfortheirremoval；
inthesamemannerthathighwayswhichwindamongmountains，bybeingmuchfrequented，becomegraduallysosmoothandcommodious，thatitismuchbettertofollowthemthantoseekastraighterpathbyclimbingoverthetopsofrocksanddescendingtothebottomsofprecipices。
HenceitisthatIcannotinanydegreeapproveofthoserestlessandbusymeddlerswho，calledneitherbybirthnorfortunetotakepartinthemanagementofpublicaffairs，areyetalwaysprojectingreforms；andifI
thoughtthatthistractcontainedaughtwhichmightjustifythesuspicionthatIwasavictimofsuchfolly，Iwouldbynomeanspermititspublication。Ihavenevercontemplatedanythinghigherthanthereformationofmyownopinions，andbasingthemonafoundationwhollymyown。Andalthoughmyownsatisfactionwithmyworkhasledmetopresenthereadraftofit，Idonotbyanymeansthereforerecommendtoeveryoneelsetomakeasimilarattempt。ThosewhomGodhasendowedwithalargermeasureofgeniuswillentertain，perhaps，designsstillmoreexalted；butforthemanyIammuchafraidlesteventhepresentundertakingbemorethantheycansafelyventuretoimitate。Thesingledesigntostripone’sselfofallpastbeliefsisonethatoughtnottobetakenbyeveryone。
Themajorityofmeniscomposedoftwoclasses，forneitherofwhichwouldthisbeatallabefittingresolution：inthefirstplace，ofthosewhowithmorethanadueconfidenceintheirownpowers，areprecipitateintheirjudgmentsandwantthepatiencerequisitefororderlyandcircumspectthinking；whenceithappens，thatifmenofthisclassoncetakethelibertytodoubtoftheiraccustomedopinions，andquitthebeatenhighway，theywillneverbeabletothreadthebywaythatwouldleadthembyashortercourse，andwilllosethemselvesandcontinuetowanderforlife；inthesecondplace，ofthosewho，possessedofsufficientsenseormodestytodeterminethatthereareotherswhoexceltheminthepowerofdiscriminatingbetweentruthanderror，andbywhomtheymaybeinstructed，oughtrathertocontentthemselveswiththeopinionsofsuchthantrustformorecorrecttotheirownreason。
Formyownpart，Ishoulddoubtlesshavebelongedtothelatterclass，hadIreceivedinstructionfrombutonemaster，orhadIneverknownthediversitiesofopinionthatfromtimeimmemorialhaveprevailedamongmenofthegreatestlearning。ButIhadbecomeaware，evensoearlyasduringmycollegelife，thatnoopinion，howeverabsurdandincredible，canbeimagined，whichhasnotbeenmaintainedbysomeonofthephilosophers；
andafterwardsinthecourseofmytravelsIremarkedthatallthosewhoseopinionsaredecidedlyrepugnanttooursarenotinthataccountbarbariansandsavages，butonthecontrarythatmanyofthesenationsmakeanequallygood，ifnotbetter，useoftheirreasonthanwedo。I
tookintoaccountalsotheverydifferentcharacterwhichapersonbroughtupfrominfancyinFranceorGermanyexhibits，fromthatwhich，withthesamemindoriginally，thisindividualwouldhavepossessedhadhelivedalwaysamongtheChineseorwithsavages，andthecircumstancethatindressitselfthefashionwhichpleasedustenyearsago，andwhichmayagain，perhaps，bereceivedintofavorbeforetenyearshavegone，appearstousatthismomentextravagantandridiculous。Iwasthusledtoinferthatthegroundofouropinionsisfarmorecustomandexamplethananycertainknowledge。And，finally，althoughsuchbethegroundofouropinions，Iremarkedthatapluralityofsuffragesisnoguaranteeoftruthwhereitisatallofdifficultdiscovery，asinsuchcasesitismuchmorelikelythatitwillbefoundbyonethanbymany。Icould，however，selectfromthecrowdnoonewhoseopinionsseemedworthyofpreference，andthusIfoundmyselfconstrained，asitwere，tousemyownreasonintheconductofmylife。
Butlikeonewalkingaloneandinthedark，Iresolvedtoproceedsoslowlyandwithsuchcircumspection，thatifIdidnotadvancefar，I
wouldatleastguardagainstfalling。Ididnotevenchoosetodismisssummarilyanyoftheopinionsthathadcreptintomybeliefwithouthavingbeenintroducedbyreason，butfirstofalltooksufficienttimecarefullytosatisfymyselfofthegeneralnatureofthetaskIwassettingmyself，andascertainthetruemethodbywhichtoarriveattheknowledgeofwhateverlaywithinthecompassofmypowers。
Amongthebranchesofphilosophy，Ihad，atanearlierperiod，givensomeattentiontologic，andamongthoseofthemathematicstogeometricalanalysisandalgebra，——threeartsorscienceswhichought，asI
conceived，tocontributesomethingtomydesign。But，onexamination，I
foundthat，asforlogic，itssyllogismsandthemajorityofitsotherpreceptsareofavail—ratherinthecommunicationofwhatwealreadyknow，orevenastheartofLully，inspeakingwithoutjudgmentofthingsofwhichweareignorant，thanintheinvestigationoftheunknown；andalthoughthissciencecontainsindeedanumberofcorrectandveryexcellentprecepts，thereare，nevertheless，somanyothers，andtheseeitherinjuriousorsuperfluous，mingledwiththeformer，thatitisalmostquiteasdifficulttoeffectaseveranceofthetruefromthefalseasitistoextractaDianaoraMinervafromaroughblockofmarble。
Thenastotheanalysisoftheancientsandthealgebraofthemoderns，besidesthattheyembraceonlymattershighlyabstract，and，toappearance，ofnouse，theformerissoexclusivelyrestrictedtotheconsiderationoffigures，thatitcanexercisetheunderstandingonlyonconditionofgreatlyfatiguingtheimagination；and，inthelatter，thereissocompleteasubjectiontocertainrulesandformulas，thatthereresultsanartfullofconfusionandobscuritycalculatedtoembarrass，insteadofasciencefittedtocultivatethemind。BytheseconsiderationsIwasinducedtoseeksomeothermethodwhichwouldcomprisetheadvantagesofthethreeandbeexemptfromtheirdefects。Andasamultitudeoflawsoftenonlyhampersjustice，sothatastateisbestgovernedwhen，withfewlaws，thesearerigidlyadministered；inlikemanner，insteadofthegreatnumberofpreceptsofwhichlogiciscomposed，Ibelievedthatthefourfollowingwouldproveperfectlysufficientforme，providedItookthefirmandunwaveringresolutionneverinasingleinstancetofailinobservingthem。
ThefirstwasnevertoacceptanythingfortruewhichIdidnotclearlyknowtobesuch；thatistosay，carefullytoavoidprecipitancyandprejudice，andtocomprisenothingmoreinmyjudgementthanwhatwaspresentedtomymindsoclearlyanddistinctlyastoexcludeallgroundofdoubt。
Thesecond，todivideeachofthedifficultiesunderexaminationintoasmanypartsaspossible，andasmightbenecessaryforitsadequatesolution。
Thethird，toconductmythoughtsinsuchorderthat，bycommencingwithobjectsthesimplestandeasiesttoknow，Imightascendbylittleandlittle，and，asitwere，stepbystep，totheknowledgeofthemorecomplex；
assigninginthoughtacertainordereventothoseobjectswhichintheirownnaturedonotstandinarelationofantecedenceandsequence。
Andthelast，ineverycasetomakeenumerationssocomplete，andreviewssogeneral，thatImightbeassuredthatnothingwasomitted。
Thelongchainsofsimpleandeasyreasoningsbymeansofwhichgeometersareaccustomedtoreachtheconclusionsoftheirmostdifficultdemonstrations，hadledmetoimaginethatallthings，totheknowledgeofwhichmaniscompetent，aremutuallyconnectedinthesameway，andthatthereisnothingsofarremovedfromusastobebeyondourreach，orsohiddenthatwecannotdiscoverit，providedonlyweabstainfromacceptingthefalseforthetrue，andalwayspreserveinourthoughtstheordernecessaryforthedeductionofonetruthfromanother。AndIhadlittledifficultyindeterminingtheobjectswithwhichitwasnecessarytocommence，forIwasalreadypersuadedthatitmustbewiththesimplestandeasiesttoknow，and，consideringthatofallthosewhohavehithertosoughttruthinthesciences，themathematiciansalonehavebeenabletofindanydemonstrations，thatis，anycertainandevidentreasons，Ididnotdoubtbutthatsuchmusthavebeentheruleoftheirinvestigations。Iresolvedtocommence，therefore，withtheexaminationofthesimplestobjects，notanticipating，however，fromthisanyotheradvantagethanthattobefoundinaccustomingmymindtotheloveandnourishmentoftruth，andtoadistasteforallsuchreasoningsaswereunsound。ButIhadnointentiononthataccountofattemptingtomasteralltheparticularsciencescommonlydenominatedmathematics：butobservingthat，howeverdifferenttheirobjects，theyallagreeinconsideringonlythevariousrelationsorproportionssubsistingamongthoseobjects，Ithoughtitbestformypurposetoconsidertheseproportionsinthemostgeneralformpossible，withoutreferringthemtoanyobjectsinparticular，exceptsuchaswouldmostfacilitatetheknowledgeofthem，andwithoutbyanymeansrestrictingthemtothese，thatafterwardsImightthusbethebetterabletoapplythemtoeveryotherclassofobjectstowhichtheyarelegitimatelyapplicable。Perceivingfurther，thatinordertounderstandtheserelationsIshouldsometimeshavetoconsiderthemonebyoneandsometimesonlytobeartheminmind，orembracethemintheaggregate，Ithoughtthat，inorderthebettertoconsiderthemindividually，Ishouldviewthemassubsistingbetweenstraightlines，thanwhichIcouldfindnoobjectsmoresimple，orcapableofbeingmoredistinctlyrepresentedtomyimaginationandsenses；andontheotherhand，thatinordertoretaintheminthememoryorembraceanaggregateofmany，Ishouldexpressthembycertaincharactersthebriefestpossible。InthiswayIbelievedthatIcouldborrowallthatwasbestbothingeometricalanalysisandinalgebra，andcorrectallthedefectsoftheonebyhelpoftheother。
And，inpointoffact，theaccurateobservanceofthesefewpreceptsgaveme，Itakethelibertyofsaying，sucheaseinunravelingallthequestionsembracedinthesetwosciences，thatinthetwoorthreemonthsIdevotedtotheirexamination，notonlydidIreachsolutionsofquestionsIhadformerlydeemedexceedinglydifficultbutevenasregardsquestionsofthesolutionofwhichIcontinuedignorant，Iwasenabled，asitappearedtome，todeterminethemeanswhereby，andtheextenttowhichasolutionwaspossible；resultsattributabletothecircumstancethatI
commencedwiththesimplestandmostgeneraltruths，andthatthuseachtruthdiscoveredwasaruleavailableinthediscoveryofsubsequentonesNorinthisperhapsshallIappeartoovain，ifitbeconsideredthat，asthetruthonanyparticularpointisonewhoeverapprehendsthetruth，knowsallthatonthatpointcanbeknown。Thechild，forexample，whohasbeeninstructedintheelementsofarithmetic，andhasmadeaparticularaddition，accordingtorule，maybeassuredthathehasfound，withrespecttothesumofthenumbersbeforehim，andthatinthisinstanceiswithinthereachofhumangenius。Now，inconclusion，themethodwhichteachesadherencetothetrueorder，andanexactenumerationofalltheconditionsofthething。soughtincludesallthatgivescertitudetotherulesofarithmetic。
Butthechiefgroundofmysatisfactionwiththusmethod，wastheassuranceIhadoftherebyexercisingmyreasoninallmatters，ifnotwithabsoluteperfection，atleastwiththegreatestattainablebyme：
besides，Iwasconsciousthatbyitsusemymindwasbecominggraduallyhabituatedtoclearerandmoredistinctconceptionsofitsobjects；andI
hopedalso，fromnothavingrestrictedthismethodtoanyparticularmatter，toapplyittothedifficultiesoftheothersciences，withnotlesssuccessthantothoseofalgebra。Ishouldnot，however，onthisaccounthaveventuredatonceontheexaminationofallthedifficultiesofthescienceswhichpresentedthemselvestome，forthiswouldhavebeencontrarytotheorderprescribedinthemethod，butobservingthattheknowledgeofsuchisdependentonprinciplesborrowedfromphilosophy，inwhichIfoundnothingcertain，Ithoughtitnecessaryfirstofalltoendeavortoestablishitsprinciples……AndbecauseIobserved，besides，thataninquiryofthiskindwasofallothersofthegreatestmoment，andoneinwhichprecipitancyandanticipationinjudgmentweremosttobedreaded，IthoughtthatIoughtnottoapproachittillIhadreachedamorematureage（beingatthattimebuttwenty—three），andhadfirstofallemployedmuchofmytimeinpreparationforthework，aswellbyeradicatingfrommymindalltheerroneousopinionsIhaduptothatmomentaccepted，asbyamassingvarietyofexperiencetoaffordmaterialsformyreasonings，andbycontinuallyexercisingmyselfinmychosenmethodwithaviewtoincreasedskillinitsapplication。