Halliday & Matthiessen (2004: 458):
Like propositions, proposals can also be reported: projected hypotactically (1) by ‘verbal’ clauses as ‘indirect speech’ or (2) by ‘mental’ clauses as ‘indirect thought’. The former involves indirect commands, offers and suggestions; the latter desired (ideas of) states of affair. One central feature they share is the mode of projected proposal: it is ‘irrealis’, or non-actualised, and the projecting clause represents the verbal or mental force of actualisation.