'Structural Coupling' is a term ( like adaptation ) which is used to refer to the systems structural correspondence with its medium. A structure-determined system is coupled to its domain of existence (medium) as long as its organisation is conserved and also as long as it conserves its congruence with the medium. Survival therefore consists in the simultaneous twin conservation of class identity and adaptation. If one of these conditions is lost then at that moment so is the other one.