is　now　some　years　since　I　detected　how　many　were　the　false　beliefs　that　I　had　from　my　earliest　youth　admitted　as　true；　and　how　doubtful　was　everything　I　had　since　constructed　on　this　basis；　and　from　that　time　I　was　convinced　that　I　must　once　for　all　seriously　undertake　to　rid　myself　of　all　the　opinions　which　I　had　formerly　accepted；　and　commence　to　build　anew　from　the　foundation；　if　I　wanted　to　establish　any　firm　and　permanent　structure　in　the　sciences。　　But　as　this　enterprise　appeared　to　be　a　very　great　one；　I　waited　until　I　had　attained　an　age　so　mature　that　I　could　not　hope　that　at　any　later　date　I　should　be　better　fitted　to　execute　my　design。　This　reason　caused　me　to　delay　so　long　that　I　should　feel　that　I　was　doing　wrong　were　I　to　occupy　in　deliberation　the　time　that　yet　remains　to　me　for　action。　　To…day；　then；　since　very　opportunely　for　the　plan　I　have　in　view　I　have　delivered　my　mind　from　every　care　＇and　am　happily　agitated　by　no　passions＇　and　since　I　have　procured　for　myself　an　assured　leisure　in　a　peaceable　retirement；　I　shall　at　last　seriously　and　freely　address　myself　to　the　general　upheaval　of　all　my　former　opinions。　　　　　　Now　for　this　object　it　is　not　necessary　that　I　should　show　that　all　of　these　are　false￥I　shall　perhaps　never　arrive　at　this　end。　　But　inasmuch　as　reason　already　persuades　me　that　I　ought　no　less　carefully　to　withhold　my　assent　from　matters　which　are　not　entirely　certain　and　indubitable　than　from　those　which　appear　to　me　manifestly　to　be　false；　if　I　am　able　to　find　in　each　one　some　reason　to　doubt；　this　will　suffice　to　justify　my　rejecting　the　whole。　　And　for　that　end　it　will　not　be　requisite　that　I　should　examine　each　in　particular；　which　would　be　an　endless　undertaking；　for　owing　to　the　fact　that　the　destruction　of　the　foundations　of　necessity　brings　with　it　the　downfall　of　the　rest　of　the　edifice；　I　shall　only　in　the　first　place　attack　those　principles　upon　which　all　my　former　opinions　rested。　　　　　　All　that　up　to　the　present　time　I　have　accepted　as　most　true　and　certain　I　have　learned　either　from　the　senses　or　through　the　senses；　but　it　is　sometimes　proved　to　me　that　these　senses　are　deceptive；　and　it　is　wiser　not　to　trust　entirely　to　anything　by　which　we　have　once　been　deceived。　　　　　　But　it　may　be　that　although　the　senses　sometimes　deceive　us　concerning　things　which　are　hardly　perceptible；　or　very　far　away；　there　are　yet　many　others　to　be　met　with　as　to　which　we　cannot　reasonably　have　any　doubt；　although　we　recognise　them　by　their　means。　　For　example；　there　is　the　fact　that　I　am　here；　seated　by　the　fire；　attired　in　a　dressing　gown；　having　this　paper　in　my　hands　and　other　similar　matters。　　And　how　could　I　deny　that　these　hands　and　this　body　are　mine；　were　it　not　perhaps　that　I　compare　myself　to　certain　persons；　devoid　of　sense；　whose　cerebella　are　so　troubled　and　clouded　by　the　violent　vapours　of　black　bile；　that　they　constantly　assure　us　that　they　think　they　are　kings　when　they　are　really　quite　poor；　or　that　they　are　clothed　in　purple　when　they　are　really　without　covering；　or　who　imagine　that　they　have　an　earthenware　head　or　are　nothing　but　pumpkins　or　are　made　of　glass。　　But　they　are　mad；　and　I　should　not　be　any　the　less　insane　were　I　to　follow　examples　so　extravagant。　　　　　　At　the　same　time　I　must　remember　that　I　am　a　man；　and　that　consequently　I　am　in　the　habit　of　sleeping；　and　in　my　dreams　representing　to　myself　the　same　things　or　sometimes　even　less　probable　things；　than　do　those　who　are　insane　in　their　waking　moments。　　How　often　has　it　happened　to　me　that　in　the　night　I　dreamt　that　I　found　myself　in　this　particular　place；　that　I　was　dressed　and　seated　near　the　fire；　whilst　in　reality　I　was　lying　undressed　in　bed！　　At　this　moment　it　does　indeed　seem　to　me　that　it　is　with　eyes　awake　that　I　am　looking　at　this　paper；　that　this　head　which　I　move　is　not　asleep；　that　it　is　deliberately　and　of　set　purpose　that　I　extend　my　hand　and　perceive　it；　what　happens　in　sleep　does　not　appear　so　clear　nor　so　distinct　as　does　all　this。　　But　in　thinking　over　this　I　remind　myself　that　on　many　occasions　I　have　in　sleep　been　deceived　by　similar　illusions；　and　in　dwelling　carefully　on　this　reflection　I　see　so　manifestly　that　there　are　no　certain　indications　by　which　we　may　clearly　distinguish　wakefulness　from　sleep　that　I　am　lost　in　astonishment。　　And　my　astonishment　is　such　that　it　is　almost　capable　of　persuading　me　that　I　now　dream。　　　　　　Now　let　us　assume　that　we　are　asleep　and　that　all　these　particulars；　e。g。　that　we　open　our　eyes；　shake　our　head；　extend　our　hands；　and　so　on；　are　but　false　delusions；　and　let　us　reflect　that　possibly　neither　our　hands　nor　our　whole　body　are　such　as　they　appear　to　us　to　be。　　At　the　same　time　we　must　at　least　confess　that　the　things　which　are　represented　to　us　in　sleep　are　like　painted　representations　which　can　only　have　been　formed　as　the　counterparts　of　something　real　and　true；　and　that　in　this　way　those　general　things　at　least；　i。e。　eyes；　a　head；　hands；　and　a　whole　body；　are　not　imaginary　things；　but　things　really　existent。　　For；　as　a　matter　of　fact；　painters；　even　when　they　study　with　the　greatest　skill　to　represent　sirens　and　satyrs　by　forms　the　most　strange　and　extraordinary；　cannot　give　them　natures　which　are　entirely　new；　but　merely　make　a　certain　medley　of　the　members　of　different　animals；　or　if　their　imagination　is　extravagant　enough　to　invent　something　so　novel　that　nothing　similar　has　ever　before　been　seen；　and　that　then　their　work　represents　a　thing　purely　fictitious　and　absolutely　false；　it　is　certain　all　the　same　that　the　colours　of　which　　this　is　composed　are　necessarily　real。　　And　for　the　same　reason；　although　these　general　things；　to　with；　＇a　body＇；　eyes；　a　head；　hands；　and　such　like；　may　be　imaginary；　we　are　bound　at　the　same　time　to　confess　that　there　are　at　least　some　other　objects　yet　more　simple　and　more　universal；　which　are　real　and　true；　and　of　these　just　in　the　same　way　as　with　certain　real　colours；　all　these　images　of　things　which　dwell　in　our　thoughts；　whether　true　and　real　or　false　and　fantastic；　are　formed。　　　　　　To　such　a　class　of　things　pertains　corporeal　nature　in　general；　and　its　extension；　the　figure　of　extended　things；　their　quantity　or　magnitude　and　number；　as　also　the　place　in　which　they　are；　the　time　which　measures　their　duration；　and　so　on。　　　　　　That　is　possibly　why　our　reasoning　is　not　unjust　when　we　conclude　from　this　that　Physics；　Astronomy；　Medicine　and　all　other　sciences　which　have　as　their　end　the　consideration　of　composite　things；　are　very　dubious　and　uncertain；　but　that　Arithmetic；　Geometry　and　other　sciences　of　that　kind　which　only　treat　of　things　that　are　very　simple　and　very　general；　without　taking　great　trouble　to　ascertain　whether　they　are　actually　existent　or　not；　contain　some　measure　of　certainty　and　an　element　of　the　indubitable。　　For　whether　I　am　awake　or　asleep；　two　and　three　together　always　form　five；　and　the　square　can　never　have　more　than　four　sides；　and　it　does　not　seem　possible　that　truths　so　clear　and　apparent　can　be　suspected　of　any　falsity　＇or　uncertainty＇。　　　　　　Nevertheless　I　have　long　had　fixed　in　my　mind　the　belief　that　an　all…powerful　God　existed　by　whom　I　have　been　created　such　as　I　am。　　But　how　do　I　know　that　He　has　not　brought　it　to　pass　that　there　is　no　earth；　no　heaven；　no　extended　body；　no　magnitude；　no　place；　and　that　nevertheless　＇I　possess　the　perceptions　of　all　these　things　and　that＇　they　seem　to　me　to　exist　just　exactly　as　I　now　see　them？　　And；　besides；　as　I　sometimes　imagine　that　others　deceive　themselves　in　the　things　which　they　think　they　know　best；　how　do　I　know　that　I　am　not　deceived　every　time　that　I　add　two　and　three；　or　count　the　sides　of　a　square；　or　judge　of　things　yet　simpler；　if　anything　simpler　can　be　imagined？　　But　possibly　God　has　not　desired　that　I　should　be　thus　deceived；　for　He　is　said　to　be　supremely　good。　　If；　however；　it　is　contrary　to　His　goodness　to　have　made　me　such　that　I　constantly　deceive　myself；　it　would　also　appear　to　be　contrary　to　His　goodness　to　permit　me　to　be　sometimes　deceived；　and　nevertheless　I　cannot　doubt　that　He　does　permit　this。　　　　　　There　may　indeed　be　those　who　would　prefer　to　deny　the　existence　of　a　God　so　powerful；　rather　than　believe　that　all　other　things　are　uncertain。　　But　let　us　not　oppose　them　for　the　present；　and　grant　that　all　that　is　here　said　of　a　God　is　a　fable；　nevertheless　in　whatever　way　they　suppose　that　I　have　arrived　at　the　state　of　being　that　I　have　reached￥whether　they　attribute　it　to　fate　or　to　accident；　or　make　out　that　it　is　by　a　continual　succession　of　antecedents；　or　by　some　other　method￥since　to　err　and　deceive　oneself　is　a　defect；　it　is　clear　that　the　greater　will　be　the　probability　of　my　being　so　imperfect　as　to　deceive　myself　ever；　as　is　the　Author　to　whom　they　assign　my　origin　the　less　powerful。　　To　these　reasons　I　have　certainly　nothing　to　reply；　but　at　the　end　I　feel　constrained　to　confess　that　there　is　nothing　in　all　that　I　formerly　believed　to　be　true；　of　which　I　cannot　in　some　measure　doubt；　and　that　not　merely　through　want　of　thought　or　through　levity；　but　for　reasons　which　are　very　powerful　and　maturely　considered；　so　that　henceforth　I　ought　not　the　less　carefully　to　refrain　from　giving　credence　to　these　opinions　than　to　that　which　i