Halliday & Matthiessen (1999: 565):
We shall examine this variation [on the cline from folk to scientific theories] with particular reference to those phenomena to which we are offering the ideation base as a conceptual alternative: the mind, knowledge, cognition — as the concerns of cognitive science. We shall suggest that the domain of cognitive science is construed ideationally within the folk model; but that this model is extended metaphorically in cognitive science itself, and this extension in fact invites the interpretation of knowledge as meaning. … Cognitive science operates with a scientific model of the individual mind; but, we shall suggest, it is one that is based fairly uncritically on certain aspects of a folk model, in particular in its selection of, and perspective on, its own domain of enquiry.