Halliday & Matthiessen (2004: 301):
… mental clauses with an Inducer …
… the mental distinction between ‘emanating’ and ‘impinging’ is … the distinction between ‘middle’ and ‘effective’.
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.
From a transitive point of view, in these initiating structures there is a feature of cause added. … From an ergative point of view, these clauses simply add a feature of agency. If the clause already has an Agent in the structure, the only way this can be done is by using an analytic causative; this makes it possible to bring in an Agent of the second order …
There is a large class of material processes of this kind where the agnate causatives are, or may be, attributive: the sun ripened the fruit/made the fruit ripen, her voice calmed the audience/made the audience calm; these will belong to the ‘initiating’ type — if we say the sun ripened, her voice calmed, the meaning changes from ‘make (ripe/calm)’ to ‘become (ripe/calm)’.
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’.