Halliday & Matthiessen (1999: 113-4):
Information is either given or demanded; in either case it is encoded as a proposition. Similarly, goods and services are either given or demanded, but the linguistic act is a mediating one, specifying the (typically non-linguistic) action that embodies the exchange, as an offer to do or a demand that something should be done. This is a proposal for a deed, one that commits either the speaker (giving) or the addressee (demanding); together with a third type, which is a combination of these two, viz. suggestion: Let’s do the laundry.