Martin (1992: 293):
For a given field, the message part realises (i) one of the features taxonomising people, places and things, or (ii) one of the actions configuring with people, places and things and entering into activity sequences, or (iii) one of the qualities associated with people, places, things and actions.
The proposal here is to present a model of field-specific semantics. The method of doing so is to interpret field as semantic descriptions of social activities and to have those semantic descriptions realised by a discourse semantic unit, the message part. That is, the level of cultural context is misconstrued as a level of language, semantics, and this semantics is then realised by discourse semantics.
This violates the theoretical principle of stratification as distinct levels of symbolic abstraction, not only because it confuses context and language, but also because it distributes the same level of symbolic abstraction, semantics, over two distinct strata.
In SFL theory, the ideational meaning realising a specific field is known as a semantic domain — the semantic profile of a field (Halliday & Matthiessen 1999: 323).