Halliday & Matthiessen (1999: 138-40):
The grammar thus draws a fairly clear line between cognition & desideration on the one hand and perception & emotion on the other. The former can create worlds of ideas, the latter cannot — at least, according to the theory of consciousness embodied in the grammar of English. Now, this difference with respect to the ability to project is one of a set of properties that collectively serve to differentiate perception, cognition, desideration and emotion as the major subtypes of sensing. These properties are summarised in Table 4(3).
