Martin (1992: 138):
Certainly the major resource as far as the grammar creating participants is concerned is nominalisation. Through this resource the grammar is able to turn a range of non-participant meanings into participant-like ones.
 It is the transitivity system of the clause that is the grammatical resource for construing experience as participants in processes.
 This construal of nominalisation is potentially misleading. Through nominalisation, meanings that are not congruently realised as participants can be metaphorically realised as wordings that construe participants.
The metaphorical form then also embodies semantic features deriving from its own incongruent lexicogrammatical properties, such that the two meanings, "non-participant" and participant, are themselves in an elaborating token-value relation within the semantic stratum, with the metaphorical Token (participant) realising the congruent Value ("non-participant").