What are the reasons for theory change in science? –To give a sober answer a comprehensible model is proposed based on the works of V.P. Bransky, P. Feyerabend , T.S. Kuhn, I. Lakatos, K.R.Popper, V.S. Scwvyrev, Ya. Smorodinsky, V.S. Stepin, and others. According to model the origins of scientific revolutions lie not in a clash of fundamental theories with facts, but of “old” basic research traditions with each other, leading to contradictions that can only be eliminated in a more (...) general theory. The model is illustrated with reference to physics in the early 20th century, the three “old” research programmes in this case being Maxwellian electrodynamics, statistical mechanics and thermodynamics. Modern example, referring to general relativity and quantum field theory, is considered. Key words: Bransky, Feyerabend, Popper, Kuhn, Lakatos, Stepin, Einstein, Lorentz, Planck. (shrink)