Halliday & Matthiessen (1999: 566-7):
The everyday folk models are likely to be embraced unconsciously by everybody in the culture, because they are everyday models, instantiated in casual conversation, and because they are construed as congruent in the cryptogrammar. The general model of the phenomena of our experience, including those of our own consciousness — seeing, thinking, wanting, and feeling — is of this highly generalised kind.
In contrast, scientific models are much more contextually constrained: they are developed, maintained, changed and transmitted within those situation types that we associate with scientific language.