Halliday & Matthiessen (1999: 225-6):
The ideational base as we have presented it so far, with its framework of sequences, figures and elements, serves well enough for construing the experience of daily life, and for organising and exchanging commonsense knowledge. But it proves inadequate to meet the semiotic demands of advanced technology and theoretical science. In the construction of scientific knowledge, the system needs to invoke the power of metaphor on a more global scale.