Halliday & Matthiessen (2014: 563):
Here the semantic relationship involves a circumstantial relationship; this was not recognised as a distinct type in traditional accounts. As noted above, enhancing relationships are essentially between figures as a whole, and only rarely can they be interpreted as holding between particular elements of a figure. Examples are typically instances of time or cause:
[verbal group:]
(He) tried, but failed, (to extract the poison). ‘although he tried, he failed’ – concession
[nominal group:]
All those on board, and hence all the crew, (must have known that something was amiss).
Film hadn’t been important until the Italians with realism and Rossellini and De Sica, then the French nouvelle vague.
Optimistu’s true nature dawned slowly. It became slightly nasty, then really rather awful, then unremittingly horrendous and then lethal only by degrees.
[adverbial group/prepositional phrase:]
(She took it) calmly enough, although not without some persuasion.
I imagined my framed survey of Xitu hanging above the fire for a few years, then being moved to the spare room, then into the bathroom, then finally being confined to the attic.
From this crossroads town follow the main road south through increasingly arid landscapes towards Rembitan, a pretty little village claiming a 17th-century mosque, then Sade, where tall, thatched lumbung (rice-barns) climb the slopes.
Again, there are some cliché-like instances, e.g. (he’s been here) thirty-five years if a day.