Halliday & Matthiessen (2004: 206):
In a ‘mental’ clause, the unmarked present tense is the simple present … But in a ‘material’ clause the unmarked present tense is the present in present …
2. Diagnostic: ‘Do’
Halliday & Matthiessen (2004: 207):
Mental processes … are not kinds of doing, and cannot be probed or substituted by do.
