Halliday & Matthiessen (2014: 711, 712):
Consider the following steps in the text:(a) Most linguists today believe that there is no good evidence ...(b) the strongest belief of all is [[ that there is no trace ... ]]… a projection sequence of figures in the semantics is realised congruently by a projection clause nexus in the grammar, and the two figures forming the sequence are realised by clauses. This is what we find in example (a); but in (b), a projection sequence has been realised not by a clause nexus but by a simple clause, and the figure of sensing is realised not by a clause but by a nominal group, while the projected figure has been realised not by a dependent ‘idea’ clause but by an embedded ‘fact’ clause. The congruent and metaphorical modes of realisation are combined in Figure 10-11. Just like interpersonal metaphor, ideational metaphor introduces additional layers of meaning that are construed by the grammar as additional layers of wording. …
