A piano can play in any key, from C major to F sharp major, and sound equally good in all of them. That was not always true. It took centuries of tuning experiments, and one of the most famous collections in music, Bach's Well-Tempered Clavier, to get there.
The tuning puzzle
If you tune a keyboard with perfectly pure fifths, twelve fifths overshoot the starting note by a small amount, the Pythagorean comma. Something has to give. Older tunings, such as meantone, made the most common keys sound beautiful, and left the far keys so out of tune that musicians simply avoided them.
Well temperament
In the late 1600s musicians such as Andreas Werckmeister described well-tempered tunings: the comma was spread across the fifths so that every key became usable, though each key kept a slightly different colour. Now a composer could move through all twenty-four major and minor keys.
Bach's Well-Tempered Clavier
Johann Sebastian Bach wrote a prelude and fugue in every one of the twenty-four keys, in two books, the first completed in 1722 and the second around 1742. He did not invent the tuning, and scholars still debate exactly which temperament he used, but the collection showed what a well-tuned keyboard could do. Mozart, Beethoven and Chopin studied it, and pianists still do.
Equal temperament: one key, two names
Equal temperament divides the octave into twelve exactly equal half steps. Every key sounds the same, only higher or lower. It became the standard tuning for pianos in the nineteenth century, and it is how your piano is tuned today. One consequence: D sharp and E flat, which a violinist may play slightly apart, are the very same key on the piano.
Why it matters for reading
On an equal-tempered piano the only question is which of the twelve keys to play. The name of the note, D sharp or E flat, matters to harmony, but your hand only needs the key. iCanPiano Style shows the key directly in the note, so music in F sharp major reads as easily as music in C major. That is exactly the freedom Bach was celebrating.
- F sharp: right half black. Play the black key to the right of F.
- B flat: left half black. Play the black key to the left of B.
- B natural: no natural sign. A note that is all black or all white is played on a white key.
Frequently asked questions
Did Bach invent equal temperament?
No. Bach championed well-tempered tuning, in which every key is usable, and wrote The Well-Tempered Clavier to show it. Equal temperament became the piano standard later, in the nineteenth century.
What is the difference between well-tempered and equal temperament?
In equal temperament all twelve half steps are exactly equal, so every key sounds the same. In well temperaments every key is usable but each has a slightly different colour.
How many preludes and fugues are in The Well-Tempered Clavier?
Forty-eight: two books, each with a prelude and fugue in all twenty-four major and minor keys.