Halliday & Matthiessen (1999: 527):
Interpersonal meaning is mapped on to ideational meaning at all points from the most micro to the most macro: from modality and speech function in the clause (or even features built in to the morphology of the word, like the diminutives characteristic of many languages) to settings affecting the whole of a particular register, like the aura of power and distance that we associate with the language of bureaucracy. These are the various ways in which language functions as a mode of action; and these meanings, no less than ideational ones, are brought into existence by the grammar.