Halliday & Matthiessen (1999: 143):
Related to the possibility of construing emotion as an Attribute is the possibility of scaling or intensifying emotive processes: many qualities can be intensified. We find sets of processes differentiated essentially according to degree of intensity — scare : terrify, horrify; and emotive processes can be intensified by means of adverbs of degree such as much, greatly, deeply. These options are also open to some cognitive and desiderative processes, although not to perceptive ones; but intensification is an essentially emotive characteristic.