Halliday & Matthiessen (1999: 614):
Semiotic systems are social systems, and meaning arises in shared social consciousness; this is evident already in the protolanguage, when infants depend on being treated as communicating beings, and those within their “meaning group” are tracking them — unconsciously creating the language along with them. We find this manifested also in the forms of discourse, in the way children participate in constructing narratives of shared experience.