Halliday & Matthiessen (2014: 33-4):
Thus any situation type can be characterised in terms of field, tenor and mode:
⦁ field – what’s going on in the situation:
(i) the nature of the social and semiotic activity; and
(ii) the domain of experience this activity relates to (the ‘subject matter’ or ‘topic’)
⦁ tenor – who is taking part in the situation:
(i) the rôles played by those taking part in the socio-semiotic activity –
(1) institutional rôles,(2) status rôles (power, either equal or unequal),(3) contact rôles (familiarity, ranging from strangers to intimates) and(4) sociometric rôles (affect, either neutral or charged, positively or negatively); and
(ii) the values that the interactants imbue the domain with (either neutral or loaded, positively or negatively)
⦁ mode – what role is being played by language and other semiotic systems in the situation:
(i) the division of labour between semiotic activities and social ones (ranging from semiotic activities as constitutive of the situation to semiotic activities as facilitating);
(ii) the division of labour between linguistic activities and other semiotic activities;
(iii) rhetorical mode: the orientation of the text towards field (e.g. informative, didactic, explanatory, explicatory) or tenor (e.g. persuasive, exhortatory, hortatory, polemic);
(iv) turn: dialogic or monologic;
(v) medium: written or spoken;
(vi) channel: phonic or graphic.