This article gives an account of cross-curricular work carried out at the Lycee Pilote Innovant du Futuroscope in the Terminale Scientifique classes (18 yrs) in science (physics and mathematics) and philosophy. We begin by giving a pedagogic justification for using a cross-curricular approach – which is one of the innovative features in our institution – by showing how philosophy can be particularly useful for cross-curricular work (philosophy has always had a special place in French education). Following this we describe the general outlines of our courses, as well as the stages and particular themes of our shared work during a year. Having set the scene, we then describe some work we do with mathematical induction. Firstly, we identify the theoretical objectives, which concern the way in which reasoning by induction may answer the scientific needs of generalisation, as compared with the experimental approach. There is a subsidiary question about the extent to which experimental science has characteristics that are in a proper sense mathematical (e.g. the idea of proof and autonomy). Secondly we produce the documents handed out to the students. These are part of a series of « route maps » with which they are familiar, since these pedagogic guides are used regularly in the lycee by the mathematics teachers. The reader who wishes to know more will find a fuller account of this cross-curricular work in the document Travaux inderdisciplinaires en terminales scientifiques published by IREM de Poitiers (1993). (ZDM/Mathdi)