Halliday & Matthiessen (1999: x):
… “understanding” something is transforming it into meaning, and to “know” is to have performed that transformation. There is a significant strand in the study of language […] whereby “knowledge” is modelled semiotically: that is, as system–&–process of meaning, in abstract terms which derive from the modelling of grammar.Halliday & Matthiessen (1999: 3):
Thus “knowledge” and “meaning” are not two distinct phenomena; they are different metaphors for the same phenomenon, approaching it with a different orientation and different assumptions. But in almost all recent work in this area, the cognitive approach has predominated, with language treated as a kind of code in which pre-existing conceptual structures are more or less distortedly expressed. We hope to give value to the alternative viewpoint, in which language is seen as the foundation of human experience, and meaning as the essential mode of higher-order human consciousness. […] What we are doing is mapping back on to language those patterns that were themselves linguistic in their origin.
