Halliday & Matthiessen (1999: 321-2):
… the first order field is the social activity being pursued (e.g. instructing somebody in how to prepare a dish, predicting tomorrow's weather, informing somebody about yellow-pages information over the phone) …
Halliday (2007 [1991]: 278):
The setting, on the other hand, is the immediate material environment. This may be a direct manifestation of the context of situation, and so be integrated into it: if the situation is one of, say, medical care, involving a doctor and one or more patients, then the setting of hospital or clinic is a relevant part of the picture. But even there the setting does not constitute the context of situation …
