Grammatical Metaphor As Theory-Building: Creating Technicality And Rationality

Halliday (2008: 97):

[Grammatical metaphor] is functional [in theory-building] in two distinct though complementary ways. 

1. On the one hand, it creates technicality. The virtual entities that come into existence through semantic junction embody a large amount of technical knowledge; and these technical terms can be organised into technical taxonomies thanks to the constructional resources of the nominal group.
2. On the other hand, it creates rationality. In the same way, by “packaging” a lot of previous information in the text, the nominalisation makes it possible to build up chains or sequences of logical argument; these are construed by the text-forming resources of the grammar (in English, the organisation of the clause into Theme and Rheme, and of the information unit into Given and New.)