Tone And Modal Assessment

Halliday & Matthiessen (2014: 170):

In English, tones also play a role in some interpersonal systems other than MOOD, viz. in certain parts of the system of MODAL ASSESSMENT. For example, speech-functional comment Adjuncts of the type ‘assurance’ are associated with tone 1, whereas those of ‘concession’ are associated with tone 4. Similarly, certain modalities are associated either with tone 1 or tone 4.