Martin (1992: 404):
Beyond this, ideational metaphor in general is a powerful measure of a text's level of abstraction and is another mode determined variable.
 To be clear, ideational metaphor is the principal means of generating abstraction in texts.
 The common feature of ideational metaphor and mode is the textual metafunction. Halliday & Matthiessen (1999: 398-9):
One manifestation of the second–order nature of the textual metafunction that is important for our purposes is grammatical metaphor. Grammatical metaphor is a ‘second-order’ use of grammatical resources…
Halliday & Matthiessen (1999: 401):
But ideational grammatical metaphors … are as it were pressed into service by the textual metafunction, to provide alternative groupings of quanta of information.In SFL theory, the realisation of the contextual system of mode in textual meaning and wording varies according to register.