Transitive Variants Viewed Ergatively

Halliday & Matthiessen (2014: 351):

By interpreting processes ergatively as well as transitively we are able to understand many features of English grammar that otherwise remain arbitrary or obscure. We will take up just one such example, that of clauses such as the police exploded the bomb, the sergeant marched the prisoners, where — as suggested by the agnate clauses the bomb exploded, the prisoners marched – the meaning is not so much ‘do to’ as ‘make to do’ (what the sergeant made the prisoners do was march). Ergatively, there is no difference between these and clauses like the lion chases the tourist. Transitively, these appear as different configurations; we have to introduce the function of Initiator to take account of the executive rôle. But in modern English they are very much alike; and the ergative analysis expresses their likeness — both consist of a Medium and an Agent.  In ergative terms, ‘a does something to x’ and ‘a makes x do something’ are both cases of ‘x is involved in something, brought about by a’.