Halliday (2008: 3):
It seemed to me that the lexis and the grammar were complementary, at least in their reality-construing, ideational function. In principle, any phenomenon of human experience could be construed either way: either lexically, as specific and open-ended, or grammatically, as generalised and closed; and hence, if some phenomenon showed a high degree of complexity, it might be construed in both ways at once.