Halliday & Matthiessen (2014: 340):
The coming of this pattern to predominance in the system of modern English is one of a number of related developments that have been taking place in the language over the past 500 years or more, together amounting to a far–reaching and complex process of semantic change. These changes have tended, as a whole, to emphasise the textual function, in the organisation of English discourse, by comparison with the experiential function; and within the experiential function, to emphasise the cause–&–effect aspect of processes by comparison with the ‘deed–&–extension’ one. … [The English transitivity system] is particularly unstable in the contemporary language, having been put under great pressure by the need for the language continually to adapt itself to a rapidly changing environment, and by the increasing functional demands that have been made on it ever since Chaucer’s time.