Halliday & Matthiessen (1999: 11-2):
The interaction base provides the resources for speaker and listener to enact a social and intersubjective relationship, through the assignment of discursive rôles, the expression of evaluations and attitudes. The base includes both the semantic strategies speaker and listener deploy in dialogic exchanges and the social personæ of the interactants. This second component is a model of the interpersonal and ideational distance between speaker and listener.