Non-Finite Clause: Theme, Transitivity And Mood

Beneficiary, Purpose Or Qualifier?

The first interpretation assumes that the prepositional phrase can be thematised:

for postgraduate studies, we need to develop good academic writing skills

The second interpretation assumes that it cannot.

The interpretation of the prepositional phrase as Beneficiary (Client), is ruled out by the impossibility of omitting the preposition:

* we need to develop postgraduate studies good academic writing skills

Halliday & Matthiessen (2014: 237):

The two functions of Recipient and Client resemble one another in that both construe a benefactive role; they represent a participant that is benefitting from the performance of the process, in terms of either goods or services. The Recipient is one that goods are given to; the Client is one that services are done for. Either may appear with or without a preposition, depending on its position in the clause (gave John the parcel, gave the parcel to John); the preposition is to with Recipient, for with Client.

Postscript:

The indeterminacy in this (constructed) clause arises from the nature of the grammatical metaphor deployed. A more coherent rendering of the metaphor would be:

we need to improve the academic writing skills of students undertaking postgraduate studies

Note also the incoherence of

we need to develop good academic writing skills for (the benefit of) postgraduate students

where the postgraduate students are construed as benefiting from someone else's improved writing skills.

'Must' & 'Have To': Obligation & Probability

Both 'must' and 'have to' can realise high value obligation or probability, the latter form evolving from an earlier conative function; see Halliday & Matthiessen (2014: 145, 572-3, 583).

 modulation: obligation (high value)

she	must	go
Theme	Rheme
Actor	Process: material
Subject	Finite	Predicator
Mood		Residue

she	has	to go
Theme	Rheme
Actor	Process: material
Subject	Finite	Predicator
Mood		Residue

modalisation: probability (high value)

she	must	have gone
Theme	Rheme
Actor	Process: material
Subject	Finite	Predicator
Mood		Residue

she	has	to have gone
Theme	Rheme
Actor	Process: material
Subject	Finite	Predicator
Mood		Residue

Un/Marked Themes In Positive And Negative Imperative Clauses

Positive Imperatives

unmarked Theme:

let's	go	home
Theme: unmarked	Rheme
Subject	Predicator	Adjunct

keep	quiet
Theme: unmarked	Rheme
Predicator	Complement

marked Theme:

you	keep	quiet
Theme: marked	Rheme
Subject	Predicator	Complement

do	keep	quiet
Theme: marked		Rheme
Finite	Predicator	Complement

Negative Imperatives

unmarked Theme:

don't	let's	quarrel	about it
Theme: unmarked		Rheme
Finite	Subject	Predicator	Adjunct

don't	argue	with me
Theme: unmarked		Rheme
Finite	Predicator	Adjunct

marked Theme:

don't	you	argue	with me
Theme: marked		Rheme
Finite	Subject	Predicator	Adjunct

Halliday & Matthiessen (2014: 103):

Theme in imperative clauses.
The basic message of an imperative clause is either ‘I want you to do something’ or ‘I want us (you and me) to do something’. The second type usually begins with let’s, as in let’s go home now; here let’s is clearly the unmarked choice of Theme. But with the first type, although the ‘you’ can be made explicit as a Theme (e.g. you keep quiet!, meaning ‘as for you, ... ’), this is clearly a marked choice; the more typical form is simply keep quiet, with the verb in thematic position. The function of the verb, in the mood structure (clause as exchange), is that of Predicator; here, therefore, it is the Predicator that is the unmarked Theme. 

In negative imperatives, such as don’t argue with me, don’t let’s quarrel about it, the principle is the same as with yes/no interrogatives: the unmarked Theme is don’t plus the following element, either Subject or Predicator. Again there is a marked form with you, e.g. don’t you argue with me, where the Theme is don’t you. There is also a marked contrastive form of the positive, such as do take care, where the Theme is do plus the Predicator take.

(The Fact That) The Bus Is 10 Minutes Late

The bus is 10 minutes late. This means that we won't be able to make it.

this (the fact that the bus is 10 minutes late)	means ('entails')	that we won't be able to make it
Token: reason	Process: identifying	Value: result

i.e. resolving the reference reveals this as a circumstantial relational clause of cause, which means it is metaphorical.  A more congruent agnate is:

Because the bus is 10 minutes late, we won't be able to make it.