Halliday & Matthiessen (2014: 34):
Thus combinations of tenor values relating to (a) status and (b) contact correlate with different semantic strategies open to speakers for demanding goods-&-services of their listeners – for commanding their listeners. If (a) the status is unequal, with the speaker being subordinate to the listener and (b) the contact is minimal, the speaker’s semantic options are very limited: it is very hard to command a stranger who is of superior status to do something; but there will be certain semantic strategies. Lexicogrammatically, these strategies will be far removed from the congruent realisation of a command, a clause of the imperative mood – perhaps something like I wonder if you would be so kind as to ... and they will be ‘dispersed’ in the grammar of mood, involving not only ‘imperative’ clauses but also ‘declarative’ and ‘interrogative’ ones and in fact not only clauses but also combinations of clauses; but semantically, they are still within range of options associated with commands. … Tenor is, as it were, refracted through semantics so that the lexicogrammatical resonances with tenor values are more indirect than the semantic ones.