Halliday & Matthiessen (2004: 452):
When something is projected as a meaning, we are not representing ‘the very words’, because there are no words. If we want to argue about whether or not the experts held this opinion, we have no observed event as a point of reference. Hence in combination with the tactic system the basic pattern for projecting meanings is not parataxis, which treats the projection as a free-standing event, but hypotaxis, which makes it dependent on the mental process clause.