The Second-Order Nature Of The Textual Metafunction

Halliday & Matthiessen (1999: 398):

The textual metafunction differs from the ideational one in a number of fundamental respects — 

its mode of syntagmatic progression is wave-like, with periodic prominence; 

it is inherently dynamic in that it organises text as process; and 

it is a second-order mode of meaning. …

The textual metafunction is second-order in the sense that it is concerned with semiotic reality: that is, reality in the form of meaning. This dimension of reality is itself constructed by other two metafunctions: the ideational which construes a natural reality, and the interpersonal, which enacts an intersubjective reality.