Halliday & Matthiessen (1999: 527):
Unlike ideational meanings, which tend to be located at definable locations in the grammatical structure, interpersonal meanings tend to be strung throughout the discourse, by an accumulation of grammatical and lexical features or by other devices such as voice quality and intonation contours. This signals the fact that interpersonal meanings are more diffuse: they relate to the figure as a whole, rather than to one of its elements; or to a whole turn in the dialogue, or even to some more extended passage of the discourse.