[...] The fundamental components of 'meaning' in language are functional components. All languages are organized around two main kinds of meaning, the ʻideationalʼ or reflective, and the ʻinterpersonalʼ or active. These components, called ʻmetafunctionsʼ in the terminology of the present theory, are the manifestations in the linguistic system of the two very general purposes which underlie all uses of language: (i) to understand the environment (ideational), and (ii) to act on the others in it (interpersonal). Combined with these two is a third metafunctional component, the ʻtextualʼ, which breathes relevance into the other two.
- Halliday (1985), Pag. XIII