When we interact with people, talking with them about something or getting something done, we construct the message in a way which allows it to fit smoothly into the speech event or text. This section looks at how the textual matafunction is realized at the sentence level in light of information theory.
Any sentence (clause) organizes the message in a certain way. (59) and (60) state the same fact, but the choice of the active or the passive voice is not without reason.
(59) Tom broke the teapot.
(60) The teapot was broken by Tom.
The starting point for the message in (59) is somebody while that for the message in (60) is something. Put in another way, the given information in (59) is Tom, a person known to both the speaker and the hearer; the given information in (60) is a specific teapot which both the speaker and the hearer have in mind. (59) answers the question “What did Tom do?”, (60) is the reply to “What happened to the teapot?” The constituent that stands for the starting-point for the message is termed theme; all the rest of the sentence is labeled rheme. The following figure illustrates the distinction.
As shown by the above figure, theme may or may not be the subject of the sentence. In a declarative sentence, the typical thematic pattern is one in which theme is conflated with the subject. In this case the theme is said to be unmarked. If another constituent of the sentence is selected as the starting-point of the message, the theme is said to be marked. If the starting-point for the message is emphasized by the pattern “It is … that/ which /who…”, the theme is termed predicted theme. If the starting-point is a comment in the form of “It is …” (as shown by the last example in the figure) the theme is called thematic comment.
The choice of theme not only directly affects the structure of the
sentence but also the text. The theme signals the maintenance of the topic
at the point of progression of the text. If you continue to write after
the sentence “Hugo spent the whole weekend in a small town”, you may choose
“He ….” or “The small town ….” as the theme of the sentence that follows
the given one. Your choice will determine how the story progresses. If
your choice is the former, the two sentences are linked by an identical
theme. If the latter, the two are linked by a succession of Rheme1→Theme2
(the new information in the preceding clause becomes the given information
of the following clause). In both cases, the theme is unmarked. Marked
themes are chosen out of the need for the creation of texture. For example,
in There he spent the rest of his life, the marked theme There
links the sentence with a place mentioned in the foregoing co-text. Predicated
theme and thematic comment are chosen when the speaker wants to highlight
a constituent or to focus on some information.
