While in Berlin, he placed himself in the forefront of European music with a treatise, ‘An Essay on the True Art of Playing Keyboard Instruments’. It was immediately recognised as a definitive work on keyboard technique. In it, he broke with tradition in allowing, and even encouraging, the use of the thumbs!
The question of posture has concerned keyboardists as far back as Carl Philipp Emanuel Bach (1714-88), whose "Essay on the True Art of Playing Keyboard Instruments" (Versuch uber die wahre Art das Clavier zu spielen) advocated sitting in the middle of the keyboard with forearms suspended slightly above the keyboard. Fingers were to be arched and muscles relaxed, and flexibility was recommended for crossing fingers, stretches and passing of the thumb. Muzio Clementi (1752-1832), who suffered defeat at the hands of Mozart in a competition staged by Emperor Joseph in 1781, ushered in a new physical approach to a recently developed instrument, the pianoforte, in his "Introduction to the Art of Playing the Pianoforte", remarkable for its allegiance to legato and its directions to keep the hand level with the forearm, to curve the fingers as appropriate and to allow little arm movement. This was followed by a three volume work by Mozart's pupil, Johann Nepomuk Hummel, entitled "A Complete Theoretical and Practical Course of Instructions on the Art of Playing the Piano Forte Commencing with the Simplest Elementary Principles and Including Every Requisite to the Most Finished Style of Performance". His instructions for sitting at the instrument require an upright torso with elbows turned toward the body, forearms level with the keyboard, rounded hands turned slightly outward, and rounded fingers close to the keys. Beethoven's student Carl Czerny (1791-1857) wrote a four-volume pedagogical work, "The Complete Theoretical and Practical Piano Forte School, from the First Rudiments of Playing to the Highest and Most Refined State of Cultivation; With the Requisite Numerous Examples, Newly and Expressly Composed for the Occasion". This espoused sitting with the upper arm slightly extended, so that the elbows are four inches closer to the keyboard than the shoulders, and the elbows about an inch higher than the upper surface of the keys, so that the forearm and hand are horizontal.
Mitchell, William J., Essay on the True Art of Playing Keyboard Instruments by Carl Philipp Emanuel Bach, trans. & ed. WJ Mitchell, Cassell And Company, Ltd., London, 1951, pp. 17-19.
But Bach's greatest achievement from these years was a composition not of music but of prose. The Essay on the True Art of Playing Keyboard Instruments remains the most famous treatise of its kind. The book combines technical advice about ornamentation, improvisation and the importance of correct fingering ("more is lost by incorrect fingering than can be compensated for by all the art and good taste in the world"). The now-standard practice of using thumbs in keyboard playing can be attributed to it. But the text also prescribes a philosophy of performance which for the first time placed the expression of emotion on a par with technical competence. "Since a musician cannot move others unless he himself is moved," the essay argues, "he must of necessity feel all of the affects that he hopes to arouse in his listeners." Both Haydn and Beethoven swore by it; its use remained widespread long into the 19th century.
Essay on the True Art of Playing Keyboard Instruments by C.P.E
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