Martin (1992: 155-6):
IDENTIFICATION has the semantic entity participant as its entry condition; its unmarked realisation is a nominal group and the people, places and things this encodes all have the potential to participate as Agent or Medium in clause structure at some point or other in a text.
 Participant as the entry condition to the IDENTIFICATION system creates a host of serious theoretical inconsistencies. For example,
- metafunction: participant is an experiential function, whereas IDENTIFICATION is a textual system;
- delicacy: the features of the system do not elaborate the entry condition, participant, but (purported) relations between participants; (cf. the entry condition 'clause' for the systems that elaborate the clause);
- function: participant is the entry condition for circumstantial features (manner/extent).
 To be clear, Martin's entire argument to justify IDENTIFICATION as discourse semantic, rather than lexicogrammatical, rests solely on "stratifying with respect to nominal group structure".
 To be clear, places are circumstantial meanings, not participants.
 To be clear, this does not define any semantic unit, let alone participant, since, through grammatical metaphor, all meaning has "the potential to be construed as an Agent or Medium in clause structure at some point or other in a text."