Halliday & Matthiessen (1999: 403):
The principle of the deployment of ideational metaphor by the textual component also applies to the bases of the semantic stratum. The text base both sets up information states within figures (presents them as messages organised around quanta of information) and guides the movement from one figure to another. In the former capacity, the text base can be interpreted as patterns stated over the ideation base. That is, the representation of ideational meaning in the ideation base constitutes the first order of representation in terms of which second–order, textual meaning can be specified.