Halliday & Matthiessen (1999: 151):
Here one participant, the Sayer, is involved as the originator of a process of symbolic (semiotic) activity, or “saying”. There may be another participant, the Receiver, whose rôle is that of ‘decoding’ what is said. What is said may itself be construed as further participant, the Verbiage; or else it may be projected as another figure [locution] within the same sequence. Finally, there may be a participant functioning as Target of the saying process.