Halliday & Matthiessen (1999: 468):
In the temporal instantiation perspective, the issue is the occurrence of the process as an event located in time: how does it unfold through time, and what is its temporal profile? Here the relevant variables are such as the following:1. Is the process homogeneous during its occurrence or does it decompose into a sequence of distinct phases (stages); is it a mini-tableau or a mini-drama?2. Is the period of occurrence a relatively short interval, or is it an extended interval?3. Is the whole period of occurrence in view or only a phase of it (e.g. beginning or end)?4. Does the process tend to occur once or repeatedly?These questions lead to typologies that include terms like stative, dynamic, perfective, imperfective, punctiliar, iterative, durative, and so on.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 dichotomy is state vs. non-state (with terminological oppositions such as stative/ dynamic); this has been favoured both by philosophers (see e.g. Nordenfelt, 1977, and his references) and by linguists (see e.g. Quirk et al, 1985 and their references). 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).