Halliday & Matthiessen (1999: 377):
The interaction base extends along the cline of instantiation. At the potential end of the cline of instantiation, the interpersonal strategies that have the move as their domain are defined by all the options persons have in exchanging meanings with one another, adopting speech roles of giving/demanding information or goods-&-services and assigning complementary roles of accepting or giving on demand to the addressee. These constitute all the patterns of interaction within a culture.