The Principle Of Ordering In The English Clause

Halliday (1994: 51-2):

Example Of The Discourse Function Of Ideational Metaphor

Halliday & Matthiessen (1999: 402-3):

In the second type [of ideational metaphor] to be exemplified, a clause or clause complex is nominalised as a Medium participant in a clause whose Process simply means 'happen' (i.e., existence of a process: happen, occur, take place; begin, continue, stop). The Medium constitutes a thematic quantum of information, as in the following example:

However, Einstein realised that if an observer was travelling alongside a light wave at the same speed as the light wave, the wave would essentially disappear, as no wave peaks or troughs would pass by the observer. But the disappearance of light waves because of the motion of an observer should not happen according to Maxwell, so Einstein concluded that either Maxwell's equations were wrong or that no observer could move at the speed of light.

Here the metaphorical clause makes it possible to summarise the preceding clause complex the wave would essentially disappear, as no wave peaks or troughs would pass by the observer as a thematic nominalised participant, the disappearance of light waves because of the motion of an observer.

Continuatives, Conjunctions And The Quantum Of Thematicity

Halliday & Matthiessen (2014: 110):

By the same token, however, since these items are thematic by default, when one of them is present it does not take up the full thematic potential of the clause in which it occurs. What follows it will also have thematic status, almost if not quite as prominently as when nothing else precedes. We can demonstrate this by reference to the concept of ‘marked (topical) Theme’. On the one hand, after a continuative or a conjunction it is still possible to introduce a marked type of topical Theme, either in contrast or as a setting ... On the other hand, such marked Themes appear to be slightly less frequent when there is some inherently thematic item in the clause, suggesting that some of the ‘quantum of thematicity’ has already been taken up.