Halliday & Matthiessen (1999: 563):
The overall ideation base thus comprises many different registerial variants — register-specific systems that we called domain models. Now, just as the overall ideation base is a theory of our total experience of the world around us and inside us — the theory that is shared by the culture as a whole, so also the different registerial variants constitute different 'subtheories' of our experience.
These 'subtheories' may complement one another by simply being concerned with different domains of experience. This complementarity is purely additive, although for society as a whole it constitutes the semiotic aspect of the division of labour, whereby different people construe different facets of the overall cultural experience.
But such subtheories may also be concerned with more or less the same domain, bringing alternative theoretical perspectives to the construal of experience that is shared. Halliday (1971) shows how this is achieved in William Golding's novel The Inheritors, by means of alternative deployments of the resources of transitivity as Golding presents the world view of two groups of early humans; these different perspectives on the shared experience are constituted as variants of the same overall transitivity system.