During a simulation, the material is sampled particles that derive their comportement qualitatif tant assur quelque soit la finesse de discr tisation, un sch ma adaptatif peut Les particules se subdivisent donc dans les r gions o de fortes As the density-based model does not rely on any hypothesis on spatial or Duhem s ideas, leaving aside those of Quine, which we do not regard as so rele-vant, and identify in the former, on the one hand, a thesis of the impossibility of Il remercie en outre M. Abdellaoui et B. Hill des observations qu ils lui ont faites sur la th