Halliday & Matthiessen (2014: 547):
What kind of projection is a fact? It is still a meaning, a semantic abstraction, not some third type differing both from meanings and from wordings (indeed, there is no third level to which it could belong). But it is not a meaning created in anybody’s consciousness, nor is it emitted by any signal source; it is simply got up so as to function as a participant in some other process – typically a relational process, but sometimes also a mental or a verbal one. Not, however, in a material process; facts cannot do things, or have things done to them.