Process Types: The Grammar Provides A Flexible Semantic Space

Halliday & Matthiessen (1999: 516):

In construing experience in this way, the grammar is providing a resource for thinking with. A strict taxonomy of separate process types would impose too much discontinuity, while a bipolar continuum would precisely be too polarised. What the grammar offers is, rather, a flexible semantic space, continuous and elastic, which can be contorted and expanded without losing its topological order. Since it evolved with the human species, it is full of anomalies, contradictions and compromises; precisely the properties which make it possible for a child to learn, because only a system of this kind could accommodate the disorder that is inherent in experience itself.