Halliday & Matthiessen (1999: 468):
The distinction most commonly drawn here is based on change. Is there change over time or not; i.e. is there a change in the course of the occurrence of the process? The most common dichotymy is state vs non-state (with terminological oppositions such as stative/dynamic)… . States and non-states have different temporal profiles. States are homogeneous; any time we check a process whose occurrence is a state, it will be the same. Non-states, or changes, are not homogeneous; during the course of the occurrence of a process something will have changed, for example the spatial location of a participant (as with processes of movement) or parts of a participant, or some other attribute of a participant (e.g. possession or location in a ‘quality space’ such as colour or temperature).