Halliday & Matthiessen (1999: 254-5):
Those illustrated here are variants of the figure => element syndrome, where only part of the figure is reconstrued as a participant…
(1) They surveyed the property => (They) did a survey of the property(2) They started to survey the property => (They) started a survey of the property(3) They discussed in the early afternoon => Their discussion took place (in the early afternoon)