Conjunctive And Modal Adjuncts vs Circumstantial Adjuncts

Halliday (1994: 84):

Propositional (Ideational) Comment Adjuncts: Occurrence

Halliday & Matthiessen (2014: 190):

The propositional (ideational) type occur only with declarative clauses. They appear at the same locations in the clause as the mood Adjuncts — though for different reasons: they are less integrated into the mood structure, being located rather according to their significance for the textual organisation of the clause. In particular, they are strongly associated with the boundary between information units — realised as a boundary between tone groups: hence the commas that typically accompany them in writing. So they often occur medially, following the item which is prominent; otherwise, they may occur as Theme, frequently as a separate information unit, or in final position as Afterthought.

Mood Adjuncts: Types & Positions

Halliday & Matthiessen (2014: 187):

These are so-called because they are closely associated with the meanings construed by the mood system: modality and temporality; and also intensity. This means that their neutral position in the clause is next to the Finite verbal operator, either just before it or just after it. But there are two other possible locations: before the Subject (ie in thematic position — those of temporality and modality have a strong tendency to function as Theme) and at the end of the clause as Afterthought.

Conjunctive And Modal Adjuncts Vs Circumstantial Adjuncts

Halliday & Matthiessen (2014: 158):

The two types of Adjuncts are also similar both in their own composition (as adverbial groups and prepositional phrases) and in how they may be differentiated from circumstantial Adjuncts. Whereas circumstantial Adjuncts fall most naturally at the end of the clause, where they carry the unmarked tonic (intonational) prominence, modal and conjunctive Adjuncts occur finally only as Afterthought and can never carry the only tonic prominence in the clause. … And while they all can occur thematically, only the circumstantial Adjuncts can normally occur as predicated Theme …

Theme Predication Vs Postposition: Afterthought

Halliday & Matthiessen (2014: 124):

A structure that can look superficially like Theme predication, but is not, is that involving postposition, where one nominal element of the clause – typically the Subject, though not always — is delayed to the end and the appropriate pronoun is inserted as a substitute in its original slot. This may be a nominal group, as in:

they don’t make sense, these instructions
shall I hang it above the door, your Chinese painting?
in some places they’ve become quite tame, the wombats

Here the Theme is, as usual, the item(s) in first position: they, shall + I, in some places; while the postposed nominal functions as Afterthought, realised prosodically by a second, minor tonic with tone 3:

// 1 ^ they / don’t make / sense these in// 3 structions //