a1 Départemant de Mathématiques et Applications, Ecole Normale Supérieure and C.N.R.S., 45 rue d'Ulm, F – 75230 Paris Cedex 05
Perturbation theory has always been an important component of the natural sciences. From celestial mechanics to the quantum theory of fields, it has always played a central role, which this little note sets out to analyse briefly. We will show, in particular, how its epistemological position has changed from being just a ‘tool’ to being the basis of definition for objects in quantum field theory.
(Received July 20 2006)
(Revised November 19 2006)