There are two main types of grammatical metaphor in the clause: metaphors of mood (including modality), and metaphors of transitivity. In the terms of our model of semantic functions, these are, respectively, interpersonal metaphors and ideational metaphors.
- Halliday (1985), a pag.321

Part of knowing a language is to know what is the most typical ʻunmarkedʼ way of saying a thing. At the same time, we also recognize that there are these other possibilities, where the unmarked mode has been departed from and the speaker or writer has chosen to encode things differently [...] So, for example, instead of 'Mary saw something wonderful', I may choose to say 'Mary came upon a wonderful sight', where the process has been represented as a material process 'came upon' and the perception has been turned into a ʻparticipantʼ 'a sight'. Or I may say 'a wonderful sight met Mary’s eyes', with the process of perception slip up into Actor 'a sight', material Process 'meet' and Goal 'eyes'; and Mary represented simply as the possessor of the 'eyes'. These are all plausible representations of one and the same non-linguistic ʻstate of affairsʼ. They are not synonymous; the different encodings all contribute something to the total meaning. But they are potentially co-representational, and in that respect form a set of metaphoric variants of an ideational kind.
- Halliday (1985), a pag.322