Martin (1992: 413):
Table 6.19. Congruent and metaphorical realisations of interpersonal meanings  mood proposal: congruent command imperative come here offer Shall/can I............. come over metaphorical command obligation you should… offer inclination I would… command projection: desire would you like… offer modulated reaction I’d love…
 In terms of the realisation of speech function by mood choice, the congruent/metaphorical distinction does not obtain for offers, because offers are not grammaticalised in the mood system. Halliday & Matthiessen (1999: 115):
Offers, in English, are not grammaticalised in the mood system; that is, while the other categories, statements, questions and commands, have corresponding mood categories in the grammar (declarative, interrogative and imperative) offers do not. They may be realised by any of the mood categories; for example:declarative: I can do the laundry.interrogative: Shall I do the laundry?imperative: Let me do the laundry!Significantly, the indicative clauses realising offers are modulated; they select for an imperative modality of readiness or obligation.
 The potential metaphor of mood in each of these instances would be the incongruent realisation of a command (semantics: speech function) in the grammar as indicative mood — declarative and interrogative — instead of imperative mood.