‘Parsons are all liars’. This was the opinion of a sergeant in a military training establishment who taught me how to ride a motor bicycle, long before I ever dreamt I would enter the parsonic ranks myself, The sergeant spoke in praise, not blame. For it was also his duty to instruct cadets in the art of expounding the mechanisms of the objects they rode, and it was his view that if parsons could speak fluently for forty minutes on stuff they could not possibly prove—and that was what he meant by saying they were liars—then cadets ought to be able to speak for five minutes, in the classical military ‘lecturette’, on the hard facts of the internal combustion engine.