We should not, perhaps, take it for granted that a description in terms of a formalised model, which has certain properties lacking in those derived … - Michael Halliday

[The construal of context as a semiotic construct accompanies the construal of language as a metafunctionally organized system because of the realizational relationship between the two. And it is this relationship which helps to explain how language is learned:]
It is this that enables, and disposes, the child to learn the lexicogrammar: since the system is organized along functional lines, it relates closely to what the child can see language doing as he observes it going on around him.

Language... is a range of possibilities, and an open end set of options in behavior that are available to the individual in his existence as social man. The context of culture is the environment of any particular selection that is made within them... The context of culture defines the potential, the range of possibilities that are open. The actual choice among these possibilities takes place within a given context of situation.

Foregrounding, as I understand it, is prominence that is motivated