Halliday (2008: 169):
The complementarity of grammar and lexis brings all of reality into focus, from the most general and all-pervasive kinds of phenomena to the most local, transitory and particular. The complementarity of system and text builds up a massive and open-ended meaning potential from countless small occasions of language use. The complementarity of speaking and writing allows for alternating between different semiotic states in resonance with the different contexts in which language functions. All of these complementarities are what lie behind the awesome power of human language.