Halliday & Matthiessen (2014: 68):
A systemic grammar is one that is organised around this concept of grammaticalisation, whereby meaning is construed in networks of interrelated contrasts. The term ‘grammaticalisation’ itself, however, is problematic; it foregrounds the sense of ‘process’ — something being turned into a grammatical system, and this obscures the point that it is the inherent nature of language to be organised in grammatical systems.