1- Changes where the organizational invariance is conserved 2- Changes without conservation of organisation A living system will last as long as its organisation is conserved and as long as it can be realised in its domain of existence. The structure of a system specifies the following four domains: 1) Domain of changes of state; all possible structural changes which the system can encompass while at the same time conserving its organisation. 2) Domain of disintegrative changes; all structural changes a system can undergo but where the organisation is destroyed. 3) Domain of perturbations; all interactions which trigger changes of state. 4) Domain of disintegrative interactions; all perturbations which trigger destructive changes in the system ( loss of organisation).