The patterns of connection and sequence within the clause which occur along the axis of chain are called STRUCTURES. That is to say, there are recurrent structural features in the way that groups combine to form clauses, and clauses to form sentences. Within the clause these relations can be identified in terms of the functions which the various constituents (groups) of the clause perform. Let us consider again an example referred to earlier.

This was identified as consisting of a nominal group followed by a verbal group followed by a nominal group. These components can also be identified in terms of the function which they serve in the structure of the clause:

These functions may be referred to as ELEMENTS of clause structure. The principle elements are:-

SUBJECT (S)

PREDICATOR (P)

OBJECT (O)

COMPLEMENT (C)

ADJUNCT (A)

The elements SUBJECT and PREDICATOR are most easily identifiable in that they exist in a relationship of concord, wherein there is an agreement of number between them, and the part which they play in determining the MOOD of the clause (whether it is declarative,  interrogative or imperative). Thus if the clause consists of P followed by an S then the mood will be interrogative, and if SP is the sequence then it is in declarative mood. The system of mood will be discussed in more detail later. In the example given above, the subject is a nominal group, and the predicator a verbal group. The subject typically identifies a principal participant in the process which is denoted by the predicator.

Whereas an object refers to a different participant in the process in addition to the subject, the complement does not identify a new participant, but rather provides some identifying or descriptive quality attaching to a participant which has already been identified by the subject or object elements in the clause.

ADJUNCTS may supply information which is additional or circumstantial to the central components of the message, as denoted by the subject, predicator, object and complement elements. They can often be identified by virtue of supplying the "why", "where", "when" and "how" type of information. In this case the adjunct may be a component of the central meaning of the clause.

Another type of adjunct may function outside the essential meaning of the clause. These may relate the clause to some other point in the text, by referring back, or indicate the speaker's attitude.

Adjuncts may be adverbial groups or prepositional groups. The sequential order of the structural elements will be discussed in more detail later, but we can note that the adjunct tends to be most mobile in the position it may take in clause structure.

Study the following examples which have been analysed in terms of their clause structure, then do the same for exercises 1 - 10. Note that the order of elements in the structure is variable.

Halliday MAK, "System and Function in Language", Chapter 5: "Categories of the theory of grammar", pages 52 - 72.