Martin (1992: 291-2):
Halliday (1985: 12) defines field of discourse as follows:
The FIELD OF DISCOURSE refers to what is happening, to the nature of the social action that is taking place; what is it [sic] that the participants are engaged in, in which the language figures as some essential component.
This is a useful starting point for interpreting the contextual semantics of experiential meaning in functional linguistics because the perspective is a social one, and because of the emphasis placed on language as action; field is not specifically tied to subject matter or topic, notions through which it can be discussed only in certain modes (it makes little sense for example when watching and listening to a rugby league training session to ask what the topic is; the appropriate question is "What is going on?").
 The term 'contextual semantics' merges two distinct strata — two levels of symbolic abstraction — in the SFL model: context and semantics. The former refers to the culture as a semiotic system, while the latter refers to a level within language. It is a clear indication that the principle of stratification is not understood in the discourse semantic model.
 The concept of 'language as action' is distinct from 'field' referring to 'the nature of the social action taking place'. For the former, Halliday & Matthiessen (1999: 354) acknowledge a cline from ‘language in reflection’ to ‘language in action’:
In situations of the ‘language in action’ kind, where the discourse is a relatively minor component of the total activity, the grammar and the semantics are obviously less constructive of the whole than in a ‘reflection’ context …
 In SFL theory, field refers to both 'what's going on' and the subject matter. The former is the first order field; the latter is the second order field (Halliday & Matthiessen 1999: 320-1).
 If the first order field ('what's going on') is watching and listening to a rugby league training session, then the second order field ('what the topic is') is the subject matter of what is said while doing so. To paraphrase Halliday & Matthiessen (1999: 354): while watching and listening to a rugby league training session itself is not constituted of language, the activity of commenting on it is. The subject matter is indispensable for modelling field.