Physics and necessity : rationalist pursuits from the cartesian past to the quantum present 7. Classical field theories. Landau Faraday and Maxwell Toward a definition of Faradayan theories The vector tensor and scalar cases Energy momentum considerations The super Faradayan approach Conclusions 8. Quantum mechanics. Historical necessity The deformation of classical mechanics Quantum logic Discreteness probabilities and information Conclusions 9. Necessity theories and modules. The preconditions of necessity Theories and modules The necessity of modularity Conclusion : the possibility of necessity 1. Rationalism in the history of mechanics. Descartes versus Newton Before Newton After Newton Conclusions 2. The necessity of classical mechanics. Connected systems Molecular mechanics Continuum mechanics Collisions Conclusions 3. From mechanical reduction to general principles. Varieties of mechanical reduction The energy principle The principle of least action Thermodynamics and statistical mechanics Conclusions 4. Geometry. From Euclid to Helmholtz Improved foundations Conventions and necessities Conclusions 5. Spacetime. From time to spacetime Rational spacetime The Helmholtzian approach with morals Conclusions 6. Numbers and math. From Descartes to the nineteenth century A historical sketch of quantity Helmholtzs Counting and measuring Poincaré on number and quantity Conclusions