Halliday & Matthiessen (1999: 567):
We can characterise them in terms of field, tenor and mode as follows (from Halliday & Martin, 1993: 54):
field: (i) extending, transmitting or exploring knowledge (ii) in the physical, biological or social sciences;tenor: addressed to specialists, to learners or to laymen, from within the same group (e.g. specialist to specialist) or across groups (e.g. lecturer to students);andmode: phonic or graphic channel, most congruent (e.g., formal 'written language' with graphic channel) or less so (e.g., formal with phonic channel), and with variation in rhetorical function — expository, hortatory, polemic, imaginative and so on.
These ranges of field, tenor and mode values define a great variety of situation types within institutions of higher education, of research and of technological development. However, these situation types are quite constrained relative to the context of culture as a whole: only certain members of the culture participate in these situation types and engage with the scientific models that are developed, maintained, changed and transmitted within them. In this respect, scientific models are clearly subcultural models: contextually they are located somewhere between the potential and the instance. If we focus on particular scientific models, such as those of the mind in cognitive science, we will find that they are even more contextually constrained.