Taxis Vs Embedding

Halliday & Matthiessen (2004: 426):

It is important to distinguish between the 'tactic' relations of parataxis and hypotaxis on the one hand and embedding on the other.  Whereas parataxis and hypotaxis are relations between clauses (or other ranking elements), embedding is not.  Embedding is a semogenic mechanism whereby a clause or phrase comes to function as a constituent within the structure of a group, which itself is a constituent of a clause … .  The embedded clause functions in the structure of the group, and the group functions in the structure of the clause.

The distinction between hypotactic and embedded expansions is set out in Halliday & Matthiessen (2004: 442) in Table 7(15).

What Is The Advantage Of Distinguishing Between Embedding And Hypotaxis?

In the case of projection, it lays the foundation for the semantic distinction between (pre-projected) facts and (projected) reports (Halliday & Matthiessen 1999: 28).

Why Projected Clauses Are Not Clause Constituents

Halliday & Matthiessen (1999: 578-9):

In our analysis (unlike that of the mainstream grammatical tradition), the projected clause is not a constituent part of the mental or verbal clause by which it is projected. There are numerous reasons for this; some of them are grammatical — for example, it cannot be the focus of theme–predication … it cannot be the Subject of a passive mental clause … it is presumed by the substitute so, which is also used to presume conditional clauses in clause complexes … But these, in turn, reflect the semantic nature of projection: this is a relationship between two figures, not a device whereby one becomes a participant inside another.