Halliday (2008: 163):
The intricacy that is characteristic of spoken language is a different manner of deploying grammatical energy, exploiting the “logical” way of looking at phenomena (note that “logical” here always refers to grammatical logic, not to formal logic — which is a designed extension of it). The principle of setting up a logical-semantic relationship between two figures is extended recursively, so that it can be extended to construe complex sequences of figures that are related systemically: in grammatical terms, a “nexus” can initiate a “complex” of any length. […] It is a powerful resource; it suits the “choreographic” spoken language, which unfold in time and builds up its own discursive momentum.