Halliday & Matthiessen (1999: 563)
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 perspectives on the construal of experience that is shared.