Halliday & Matthiessen (2014: 352):
The ergative structure is open–ended, and a further round of agency can always be added on:the ball rolled : Fred rolled the ball : Mary made Fred roll the ball : John got Mary to make Fred roll the ball : …The transitive structure, on the other hand, is configurational; it cannot be extended in this way. Thus, from a transitive point of view, Mary made Fred roll the ball is not a single process; it is two processes forming one complex.