What is clear from this brief survey is that technical difficulty can be agreed upon for most of the pieces in the ‘Well-Tempered Clavier’, but finding universal acquiescence regarding musical difficulty and challenge is another realm entirely. Presently the E major Prelude and Fugue (BWV 854) is the first option of the current specification illustrating the technical challenges that this piece presents and the expectations of pianistic maturity perhaps required to play this piece competently. Similarly, Trinity College London does not include any of the ‘Well-Tempered Clavier’ until their Grade 8 examination for piano. No other works from the ‘Well-Tempered Clavier’ are included in the examination syllabus at earlier grades although other works from Bach are there. For example, Grade 8 Piano (the level just down from a Diploma), includes the ‘Prelude and Fugue’ in G (BWV 884) from the second book. This grading of difficulty is often seen as a reliable source of information when trying to judge the difficulty of the Well-Tempered Clavier pieces, amongst others.
The Associated Board of The Royal School of Music, London includes many of Bach’s works on their published practical examination list (2020-2021). None of either Book 1 or Book 2 is graded above a level 7 by Henle. At the higher end of difficulty is the prelude in B minor (BWV 869), at level 6, and its accompanying fugue at level 7. Interestingly, they also rate the E major prelude (BWV 854) at level 4 with its companion fugue coming in at level 6. I would also add that like the pieces themselves that spanned a considerable period of JS Bach’s life, these preludes and fugues are also a lifetime occupation, ambition, or pursuit evolving with you as you grow in musical understanding and technical strength. The element to keep in mind is that even if a piece in the collection is loosely described as ‘easy’, to play it competently is never an easy challenge.
Fortunately, many of these pieces have been chosen as pieces for examination purposes and therefore have been attributed to a broadly agreed standard of difficulty. Measuring the difficulties of any given piece of music is the subject of healthy debate. The idea of equal temperament tuning had been in the minds of scholars many years before but Werckmeister can perhaps be credited with spurring the concept further, that by the end of Bach’s life had taken firm hold. Bach had allegedly been an advocate of the equal temperament tuning system and tuned his own keyboards using this concept. In 1691 Andreas Werckmeister (a notable organist of his time), proposed a system of tuning that divided the octave into twelve equal intervals.