Something I have done no research into: are there studies (physical, philosophical) of the way in which processes or activities are constrained into stages? Are, that is to say, not smoothly continuous but lumpy, jerking at particular points: think of melting points, boiling points, the different gaits of animals. Transitions that have a definite – and often apparently arbitrary – structure. Could there be something to be learnt from comparative studies of these kinds of phenomena? If we know the world to be real because it resists our desires, might such a study of constraint offer revelations about its structure?