Halliday & Matthiessen (1999: 140):
While both cognition and desideration project ideas, they project ideas of different kinds. Cognition projects propositions — ideas about information that may or may not be valid: he believed/imagined/dreamt —> that the earth was flat. In contrast, desideration projects proposals — ideas about action that has not been actualised but whose actualisation is subject to desire: he wanted/intended/hoped for —> her to leave. Projection is the critical link between sensing and saying.