Halliday & Matthiessen (1999: 508):
For understanding physical systems, the critical approach was that of measurement; the dominant theme was mathematics, and the perspective essentially a synoptic one. But this did not serve well for interpreting biological systems; these are better understood in terms of change, so the perspective had to be altered, to become dynamic, with evolution as the dominant theme. For social systems, however, the dynamic perspective by itself lacked explanatory power, and in the present century it was overtaken by another synoptic approach, the theme of structuralism. Our conception of the nature of social systems has been largely moulded in structuralist terms.