Halliday & Matthiessen (1999: 183):
Experientially, [in a nominal group] there is a ‘carrier’ — the Thing — and there are ‘attributes’ — Epithets and other modifiers. However, participants are construed not only experientially but also logically, which means that the Thing (typically) serves as a Head that can be modified by successive attributes and that this modifying relation is inherently ascriptive. There is thus no equivalent, in the nominal group, of the Process in an ascriptive figure; this is construed instead as the logical relation of modification, indefinitely repeatable. […] That is, participants are construed as things that can accrue attributes.