Definitions Theme

9
Theme and rheme
Theme and rheme are considered elsewhere on the site because the concepts are applicable in a number of areas (genre-based approaches, the use of the passive, academic writing, fronting, markedness and much more). There are links below to some of these guides.
This guide is concerned with investigating the idea a little more thoroughly and is based on a functional linguistics approach, primarily the work of Halliday (1994 and elsewhere) and subsequent authors.
Within that approach, language is a social semiotic which means that it is the key way in which we human beings acquire knowledge, express experience, attitudes and values and construct our view of reality. Semiotics is the branch of linguistics and philosophy which is concerned with signs and symbols and language is, above all, a system of signs.

Definitions

Theme

is defined by Halliday (1994: 38) as:
what the message is concerned with: the point of departure for what the speaker is going to say
For example in sentences such as:

• 
  The man told me where to go
  The theme is The man because that is what the sentence is all about.
  
• 
  My house in London is valuable but not for sale
  The theme is My house in London.
  

We should not, however, confuse theme with subject, which is a grammatical rather than a communicative category, or agent, which is a different grammatical category present in passive expressions, because, for example:

• 
  in a sentence such as:
  Yesterday afternoon, we went to the park
  The theme is Yesterday afternoon, because, in communicative terms, that is what the speaker is talking about. It is not, however, the grammatical subject but an adverbial noun phrase. The subject is we but that does not occur as the theme because it is actually part of the rheme.
  
• 
  in a sentence such as:
  Spending time at the zoo is just what the children like best
  The theme is Spending time at the zoo which is also the grammatical subject but formed by nominalising a non-finite verb phrase.
  
• 
  in a sentence such as:
  Because it was raining, we stayed in and watched TV
  The theme is Because it was raining and that is a clause in itself and not the subject of anything. It is, however, also a subordinate clause which cannot stand alone and make sense.
  
• 
  in a sentence such as:
  The grass is kept short by the sheep
  The theme is The grass which is a noun subject but not the agent (it is the patient in a passive sentence).
  
• 
  in a sentence such as:
  The people who wanted a refund went to the manager's office
  The theme is The people who wanted a refund because that relative clause structure is the starting point from which the rest of the utterance may be understood.
  
• 
  in a sentence such as:
  Over that hill and across the bridge is where you need to go
  The theme is Over that hill and across the bridge which is a combination of two prepositional phrases. In functional grammar, the prepositional phrases would usually be described as location Circumstances, by the way, but, in this case, Circumstances functioning as themes.
  
• 
  in a sentence such as:
  The car has been repaired
  The theme, rather obviously, is the car because that is what the rest of the clause is concerned with. It is not, however, the subject of the verb, it is, in grammatical terms, the patient (i.e., the entity on which the verb acts) and the agent (perhaps the workshop or the mechanic) is absent in this case because it is of no importance or already known to the hearer / reader and need not be made explicit.