Halliday (2008: 120):
The network is a theory of the system — that is, of the linguistic system, at any one stratum, as a whole. It is a paradigmatic theory, because the concept of system itself is paradigmatic. […] Any theory of possibilities is essentially paradigmatic. It is by networking the system that we show, not just how meaning is made, but how it is possible for meaning to be made. The system networks of the grammar are an attempt to state the possibilities of the grammar as a whole, its total potential for construing meaning in wording.