Halliday & Matthiessen (2014: 524-5):
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 the projected proposal: it is ‘irrealis’, or non-actualised, and the projecting clause represents the verbal or mental force of actualisation. The mode is reflected in the realisation of the reported clause. (Both mental and verbal reporting of proposals can be used to realise direct proposals).