Halliday & Matthiessen (2004: 597):
At one pole, the experience of the flow of events is construed as two distinct quanta of change… . At the other pole, the experience of the flow of events is construed as a component part of quantum of change… . Intermediate between these two poles are various manifestations that represent a move from two distinct quanta of change via two interdependent ones to a single one. The scale is thus one of degree of integration of two quanta of change. This scale of integration is based on the rank scale.