 the complex nature of inter-theoretical relations and the relationship between theory and experience, constitute a common ground for questioning.3 The first part of our article concerns the changes in epistemological consensus at the turn of the century. The second part will be devoted to Poincaré's reflections on the status of physical geometries and physical theories, as they appear in his texts written around 1890. Then we analyze the first reflections of Pierre Duhem on physical theory, in particular his thesis of the hypothetical/symbolic character of physical theories and his criteria for selecting good theories, partly associated with his ideal of physical theory; the whole set of considerations, highlighting the Poincarean inspiration. The relationships between the scientific practices of the two scholars, the contemporary theoretical context and their reflections will drive this investigation.4 Changes in Scientific Consensus Between the last years of the nineteenth century and the beginning of the 1910s, experimental access to the intimate structure of matter favored a consensus on the relevance of atomistic hypotheses of statistical mechanics. The French notably Poincaré, Becquerel, Curie, Langevin and Perrin contributed to this evolution, associated with the physics of electrons and ions, new radiations and Brownian motion. In 1905, the Société Française de Physique invited H. A. Lorentz to speak on "Thermodynamics and kinetic theories". He distinguishes between two kinds of theories in mathematical physics. There are those which seek to "penetrate the intimate mechanism of phenomena" and those which, using certain general principles, establish relations between quantities "directly accessible to observation". Given the state of contemporary research, the fields of application of the two theories, which are taken as examples, are different and each one proves itself powerless where the other makes it possible to reveal relationships (Lorentz 1905, 533-534). This same pluralistic perspective can be found in Jean Perrin's book Les principes (1903), dedicated to thermodynamics. In the preface, Perrin states that molecular hypotheses correspond to the "deductive method", which "consists in imagining a priori for matter a structure whose direct perception still escapes our imperfect senses, and such that its knowledge would make it possible to deduce the 3 Poincaré was a member of the jury of the (second) doctoral thesis of Duhem (1888); the only known correspondence between the two is of this period and without epistemological interest (Poincaré 2007, 157-158). Around 1890, Poincaré saw Duhem as the great French specialist in thermodynamics (Poinc
the complex nature of inter - theoretical relations and the relationship between theory and experience, constitute a coarse earth for questioning.3 The first part of our article concerns the change in epistemological consensus at the turn of the hundred. The second part will be devoted to Poincaré's reflections on the condition of forcible geometries and physical theory, as they appear in his texts write around 1890. Then we analyze the first reflections of Pierre Duhem on physical theory, in particular his dissertation of the hypothetical / symbolic character of forcible theories and his criteria for selecting good theories, partially associated with his ideal of forcible theory; the whole set of considerations, highlight the Poincarean inspiration. The relationships between the scientific practices of the two scholars, the contemporary theoretical context and their observation will drive this investigation.4 Changes in Scientific Consensus Between the last years of the nineteenth century and the beginning of the 1910s, experimental access to the intimate structure of matter favored a consensus on the relevance of atomistic hypothesis of statistical mechanics. The French notably Poincaré, Becquerel, Curie, Langevin and Perrin contributed to this development, consociate with the purgative of electrons and ions, new radiations and Brownian motion. In 1905, the Société Française de Physique invited H. A. Lorentz to speak on " Thermodynamics and kinetic theories ". He identify between two kinds of theories in mathematical physics. There be those which seek to " penetrate the intimate mechanism of phenomena " and those which, using certain cosmopolitan principle, establish relations between quantities " directly accessible to observation ". Given the state of contemporaneous research, the battlefield of application of the two theories, which are aim as examples, are unlike and each one proves itself powerless where the other makes it possible to reveal relationship (Lorentz 1905, 533 - 534). This same pluralistic position can be found in Jean Perrin's book Les principe (1903), dedicated to thermodynamics. In the preface, Perrin states that molecular hypotheses correspond to the " deductive method acting ", which " consists in imagining a priori for matter a social organization whose direct perception still escapes our fallible senses, and such that its knowledge would make it possible to deduce the 3 Poincaré was a penis of the jury of the (second) doctoral thesis of Duhem (1888); the only know correspondence between the two is of this period and without epistemological interest (Poincaré 2007, 157 - 158). Around 1890, Poincaré saw Duhem as the great French specialist in thermodynamics (Poinc
 thf complex nature of intev-theoretical relcrions end the relatiovship between theory and expxriebce, cinstitute a common grojnd for qlestionint.3 Tht first part of ond article condcrns chx changes in eplstemologicdl consensus ad ghz turn of the century. The second pare will ne devoted to Poyncagé's refmvcuions on the status of physical gsometrits and physical throries, as they appear in hls tfxts written arounf 1890. Then we qnalrze the first reflections of Pierre Duhem on physical theory, in pafticukar his thgsjs mf the hypovheticwl/symbolic cmsractes of phusical theoriex aid hus criteria for selecving good theories, pwrtly assmcnated with his ideal if physhcal theuey; ghe wiols set lf ronsideratikns, highligyting the Poincaream ybspiration. Ths relaeijnships between the scientific practicev or the two scholars, the xontemporary theoretifal contevt and their reflections will drive this investigdtion.4 Zhauncs iv Sfientific Consensus Between the last years of fht npneteenth century and the bebijnogg of the 1910s, ebperimzhtzl access to the ijtimate struxture of iattrr favored a consensus on tye relevance if atomistic hypotkeses of stacisticsl mevhanics. The French notayly Pojncaré, Becqufrel, Curis, Langevin and Pefrik cmntributta to this evolutijn, associeted cith the phyxics os electrond and ions, new radiationd and Bsownian mohion. In 1905, the Société Française de 'iysique invitgd V. A. Lorentz to sieak on "Thermodrnamics and kiuetic thzories". He distinfuishes between twj kinds of thalries in matiematical phywics. There xfe those which seek to "ieuetrate tye intimate mechanlsm ow phenomena" and ckowe which, using vergaig heieral [rinciples, evtabuisf relagions btcwecn duanyities "directly accevsibme to observation". Biyen the sjate of cjntemporary rrsearch, the fields of a'plicavion og tre two theories, which are takeh as examolef, are differqnt qnd each one proves itself powerless where the othec makes it possible to eeveal relationshipx (Lorentz 1905, 533-534). Vhis swme pluranistic perspective cqn be found in Jesn Perrin's book Les pdincipas (1903), dfdicated to thermodynamics. In the preface, Perrin states that molecular hypothesxs correspond to yhe "dvduetire methjd", wiirh "consists in imsgining a priori for matter a svructure wvofe direct perception still excxpes our impetfect senses, and such that its knoeledge would make it possible tp deduce the 3 Poincaré wax a membwr of the jlty uf the (second) doctpral tkesis if Duhen (1888); tme only known zortedpondence betxeeu the two is of this period and wuthout eoistemological iiterest (Poingavé 2007, 157-158). Arkund 1890, Koincaré saw Duhem as fje grgat French spevialist in thetmodynamics (Poinc
the complex nature of inter-theoretical relations and between and experience, a common ground of article concerns the in epistemological consensus the turn of the century. The part will be devoted to Poincaré's reflections on the status of physical geometries physical theories, as they appear in his texts written around 1890. Then we the reflections Pierre on physical theory, in particular his thesis of the hypothetical/symbolic character of physical theories and his for selecting good theories, partly associated with his of physical theory; the set of considerations, highlighting the inspiration. relationships between scientific of two scholars, the theoretical context and their reflections will drive this investigation.4 Changes in Scientific Consensus Between the last years the nineteenth the beginning the experimental to the intimate matter favored a consensus on the hypotheses of statistical mechanics. The French notably Poincaré, Curie, Langevin Perrin contributed to this evolution, associated the physics of electrons and ions, new radiations Brownian motion. In 1905, the Société Française de Physique invited H. A. Lorentz to speak and kinetic theories". He between two kinds theories mathematical There those which to "penetrate the intimate mechanism of phenomena" and those which, using general principles, establish relations between quantities "directly accessible to observation". state contemporary research, the of application of the theories, are taken as examples, and one where other it possible to reveal (Lorentz 1905, 533-534). This same perspective can be found principes (1903), dedicated to thermodynamics. In the preface, states that molecular hypotheses correspond to the method", which "consists in imagining a priori for matter a structure whose perception still imperfect senses, and such that its knowledge would it possible to deduce 3 Poincaré was a member of the jury of (second) thesis of (1888); the only correspondence between the is of this without epistemological (Poincaré 157-158). saw Duhem as the great French in (Poinc
 the complex nature of inter-thEoretical rElatiOns And ThE relAtioNship between thEOry aNd experience, constitute A commOn GRounD FoR quesTioning.3 tHe FIRst PaRt Of oUr ARtIcle cOncErns the Changes in ePisTeMological conSEnSus at the tuRn oF the century. THe sEcond pArT wiLL be deVotEd to POincarÉ'S refleCtions on tHe STatus oF PhysicaL GEoMetrIes and physical theORiES, as they appear iN his teXtS WrITTen AroUnd 1890. Then we aNaLyze tHE first rEFlECTIonS Of Pierre Duhem On physical tHEorY, in parTiCulAR his thEsis oF tHE hyPothetical/sYmboLic characTer of pHYsical tHEories aNd his cRitEriA for SElEcTinG gOOd tHEoRieS, ParTly assocIaTeD with His iDEAL Of phYsiCal tHeory; The whole set of ConSideRAtiOns, hiGhligHtinG tHe PoiNcareaN inspIrAtion. The relatioNshiPs between The ScIenTiFic prACtices Of tHe tWo scholArs, the cONteMpORARy Theoretical context AnD THeIr reflecTions wILl DrIVe this inVeStiGatiON.4 changEs in sCiEntific COnsensUS BEtWeen the LaSt yearS oF thE niNeteeNTh ceNtury aNd the begInninG Of the 1910s, experimeNTal access to thE InTIMaTE strUctUre of matter FavoREd a cOnseNSuS on THe relEvancE oF AtOMistic hypotheses of sTaTisticAl mecHanics. The FrenCh notably POINCaré, BecqUereL, cuRIe, Langevin and PErrin ContributeD To this evOlutiOn, associAted with tHE Physics oF elEctRonS anD IOnS, new radiationS ANd BrOwNian motIon. in 1905, the SoCiéTé FRanÇaiSe De PhysiquE invited h. A. loReNtZ to Speak ON "ThermodYnAmiCs And KinetIC theorIes". He DistInGuISheS betweeN TwO KInds Of ThEoriEs iN mAthemAticAL phYsics. ThEre are thoSe wHIch sEeK tO "penetrAte the intimatE mEchanism of PhEnoMena" anD THose whicH, using certain general priNCiples, eStaBlish RelaTions betwEen QuantiTieS "DirectLy acceSsiblE tO obSERvatiON". giVen ThE state of coNTEmpOrary ReSearCh, the fiElds of application oF The Two theories, whIch Are tAKEn As eXAmPLes, ArE DifFERent and each one pRoves itselF pOWeRless where THe oThEr makes It possiBle to REveal reLationshiPs (Lorentz 1905, 533-534). thIs saME PluRalistic peRspectivE can be fouND in JeAN PErrin'S boOk Les pRiNciPes (1903), deDicateD To tHermoDynamiCs. in the pRefacE, PErrin staTes that molecular hypotheSes corRespoNd tO the "deducTivE MetHod", which "cOnsiSts in imagiNinG a pRiori For MAtter A strUCtUre WHose dIrecT PerceptioN StIll ESCaPes our imperFECT seNses, aNd sUCh that Its kNowledge would make IT possible to dedUce tHE 3 poiNcaRÉ was A mEmber of the jury Of tHe (SECond) doctOrAl thesis of DUhem (1888); the oNlY Known CorresPondenCe betweEN ThE Two is oF thiS peRiod and wiThoUt EPistemoLoGiCAl inteRest (poIncaré 2007, 157-158). around 1890, pOincARÉ saw Duhem as the grEat FrENCh speCIalIst in ThErmodynAMics (poinc
 the complex nature of int er-theoret icalrel ati on s an d th e relationship betw een theory and experie nce,co n stit u te  a co mmon gr o un d for  q ue sti on i ng .3 Th e f irst pa rt of ourart ic le concernst he  changes i n e pistemologic alconsen su s a t  thetur n ofthe ce n tury.The secon dp art wi l l be de v o te d to  Poincaré's refle c ti o ns on the stat us ofph y si c a l g eom etries and  p hysic a l theor i es , a s t h ey appear inhis texts w r itt en aro un d 1 8 90. Th en we  a n aly ze the firs t re flections  of Pi e rre Duh e m on ph ysical  th eor y, i n  p ar tic ul a r h i sthe s isof the h yp ot hetic al/s y m b o liccha ract er of  physical the ori es a n d h is cr iteri a fo rselec ting g ood t he ories, partly a ssoc iated wit h h is  id ea l ofp hysica l t heo ry; the  wholes etof c o ns iderations, highli gh t i ng  the Poi ncarea n  i ns p iration.  T herela t i onshi ps b e tw een thescient i fi cpractic es  of th etwo  sc holar s , th e cont emporary  theo r etical context and their ref l ec t i on s  wil l d rive this i nves t igat ion. 4  C han g es in  Scie nt i fi c  Consensus Betweenth e last  year s of the nine teenth cen t u r y and th e be g in n ing of the 191 0s, e xperimenta l  accessto th e intima te struct u r e of mat ter  fa vor eda co nsensus on th e rele va nce ofato mistichyp oth ese s o fstatistic al mecha ni cs .Th e F rench notablyPo inc ar é,Becqu e rel, C urie,  Lan ge vi n  an d Perri n  c o n trib ut ed  tothi sevolu tion ,  as sociate d with th e p h ysic sof  electr ons and ions,  n ew radiati on s a nd Bro w n ian moti on. In 1905, the Sociét é  França ise  de P hysi que invit edH. A.Lor e ntz to  speak  on " Th erm o d ynami c s  a ndki netic theo r i es" . Hedi stin guishes  between two kinds oftheories in m ath emat i c al  ph y si c s.Th e rea r e those which s eek to "pe ne t ra te the int i mat emechani sm of p henom e na" and  those wh ich, usin gcert a i n g eneral pri nciples,  establis h  rela t io ns be twe en qua nt iti es "d irectl y  ac cessi ble to  o bserva tion" .Given th e state of contemporary  resea rch,the  fields o f a p pli cation of  the  two theor ies , w hichare taken  ase xa mpl e s, ar e di f ferent an d  e ach o ne  proves its e l f  po werle ssw here t he o ther makes it pos s ible to reveal  rel a t ion shi p s (L or entz 1905, 533 -53 4) . This sam epluralistic  perspec ti v e can  be fo und in  Jean P e r ri n 's boo k Le s p rincipes(19 03 ) , dedic at ed to the rmod yn amics.  In th e  pre f a ce, Perrin state s tha t molec u lar  hypo th eses co r resp ond to the  "deductive  metho d",which  "consi st s in i mag in ing a prio r i for mat ter a  struct ur e wh ose  direc t pe r c eptio n st il l e scapes ou r im p er fe c t s ense s, an dsuch  that its knowledg e w o uld mak eitp o ssible to d educe the3 P oinca r é  was a mem b er o f  t h e jur y of t he (se cond) d o cto ra l thesi s o f Duhem (18 88); theo nly  k nown  corresp on denc ebet we en the two is o f this p eriod an d withou t e p iste m ologic al  interest (P oinca ré 2007, 1 5 7 -15 8). Aro u nd189 0,Poin car é sa w  Duhem as the great Fren ch s pecia l ist  in t hermo dy namics ( P oinc 
 the_complex nature_of inter-theoretical relations and_the relationship_between_theory and_experience,_constitute a common_ground for questioning.3_The first part of_our article concerns_the_changes in epistemological consensus at the turn of the century. The second part will_be_devoted to_Poincaré's_reflections_on the status of physical_geometries and physical theories, as_they appear_in his texts written around 1890. Then we_analyze_the first reflections_of Pierre Duhem on physical theory, in particular his_thesis of the hypothetical/symbolic character of_physical theories and_his_criteria_for selecting good theories,_partly associated with his ideal of_physical theory; the whole set of_considerations, highlighting the Poincarean inspiration. The relationships_between the scientific practices of the_two scholars, the contemporary theoretical_context and_their reflections will drive this_investigation.4 Changes in_Scientific Consensus_Between the last_years of the nineteenth century and_the beginning of_the 1910s, experimental access to the_intimate_structure of matter_favored_a_consensus on_the relevance of_atomistic_hypotheses of_statistical_mechanics. The French notably Poincaré, Becquerel,_Curie,_Langevin and Perrin contributed to this evolution,_associated with the physics_of_electrons and ions, new_radiations and Brownian motion. In_1905, the Société Française de Physique_invited H._A. Lorentz_to speak on "Thermodynamics and kinetic theories". He distinguishes between two_kinds of theories in mathematical physics._There are those which_seek to_"penetrate_the intimate mechanism_of_phenomena" and_those which, using certain general principles, establish_relations between_quantities "directly accessible to observation". Given_the state of contemporary_research,_the fields of application of the_two theories, which are taken as_examples, are different and each_one_proves_itself powerless where the other_makes it possible to reveal relationships_(Lorentz 1905, 533-534)._This same pluralistic perspective can be found_in_Jean Perrin's book Les principes (1903),_dedicated_to thermodynamics. In the preface, Perrin_states_that_molecular hypotheses correspond to the_"deductive method", which "consists in imagining_a priori for matter a structure whose direct perception_still escapes our_imperfect senses, and such that_its_knowledge_would make it possible to deduce the 3 Poincaré was_a member_of the jury_of the (second) doctoral thesis of Duhem (1888); the only_known correspondence between the two is of_this period and without epistemological interest (Poincaré 2007, 157-158). Around 1890,_Poincaré saw Duhem as the great French specialist_in thermodynamics (Poinc