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.