 Lakatos found multiple, vying research programmes to coexist, taking turns at leading in scientific progress.A research programme stakes a "hard core" of principles, such as the Cartesian rule "No action at a distance", that resists falsification, deflected by a "protective belt" of malleable theories that advance the hard core via "theoretical progress", spreading the hard core into new empirical territories.Corroborating the new theoretical claims is "empirical progress", making the research programme "progressive"—or else it "degenerates".