Bach's Fugue in C major, BWV 846, is the second piece in Book I of The Well-Tempered Clavier. Most people know the prelude that comes before it; this fugue is what the book was actually written to prove. Twenty-seven bars built from a single subject a bar and a half long, entering one voice at a time until four lines are running together. The full piano score is on screen, note by note.
The whole book exists to prove one thing: every key can be played
In 1722 Bach gathered twenty-four preludes and twenty-four fugues into one book and called it The Well-Tempered Clavier — all twenty-four keys.
At the time this was an argument. The way keyboards were tuned then left some keys sounding audibly out of tune, so composers in practice used only a handful and the rest might as well not have existed. With a whole book Bach said: tune it differently and all twenty-four are usable, and each one has a character of its own.
He wrote the purpose on the title page himself: for the use of young musicians eager to learn, and for the diversion of those already skilled.
This prelude and fugue are the first pair in the book, in C major, with no sharps or flats in the key signature. It is the door into the whole collection — Bach put the plainest key at the front, and the other twenty-three follow. A plain key signature does not mean white keys only: where this fugue moves into A minor and D minor, sharps and flats appear all the same.
It starts with one voice and ends with four standing together
It opens with one line: four notes stepping upward, then a turn and a fall, done in a bar and a half. That one sentence is the only material in the piece.
A second line comes in with the same sentence at a different height while the first keeps going. Then a third, then a fourth. By the middle, four lines are running at once, each going its own way, and every one of them still saying the same sentence.
You do not have to follow all four. Pick one and stay with it — you will find it constantly interrupted and never once covered over. That sense of being crowded together while everyone remains audible is what a fugue is for.
At the end the four lines close on one chord together. The whole thing takes under two minutes.
Twenty-seven bars of one subject stacked again and again
Twenty-seven bars, 4/4, 784 notes in four voices. By bar 5 all four voices are in, thirty-odd notes to the bar, and the density mostly stays there.
In the middle the subject is repeatedly stacked on itself: one statement has not finished before the next begins.
At bar 14 the count drops to seventeen, the one breath mid-piece, then builds straight back.
At bar 20 the bass reaches E2 and holds the floor from there. From bar 24 it closes, and the highest note of the piece, C6, arrives in the last bar as all four voices stop together.
There is not one slur in this score. The tempo word Moderato e maestoso, the dynamics and the hairpins were added by a nineteenth-century editor — Bach's manuscript has only the notes — and this performance follows that edition's markings.
The source file had three copying errors: a G missing its sharp in bar 12, a bass F given a sharp it should not have in bar 13, and a bass A left out entirely in bar 14. All three are corrected here against the 1866 Bach-Gesellschaft edition.
The difficulty is not the fingers; it is reading four lines at once
The notes are not fast and the spans are not wide; the difficulty is voicing.
First, reading. Four lines are laid across two staves and one hand often has to take two of them, so mark each line in a different colour before you play or it turns into a block of chords.
Second, the subject has to be audible. Every time it enters it needs to be a little clearer than what surrounds it, without becoming a knock. Whichever finger has it gets a little more.
Third, joining notes. There is almost no pedal to lean on here; the fingers have to carry the line, so finger substitution and silent changes come up more than in most pieces.
The tempo is the ♪=116 printed on the score — an eighth-note beat, equal to 58 to the quarter — and the finished video runs one minute fifty-eight. That beat unit is easy to misread: taking 116 as the quarter would play it twice as fast.
We rate this 4 out of 5.
The piece that comes before it under the same number, and the other keys in the book
The piece before it under the same number, BWV 846, is the Prelude in C major, already on this channel: https://www.youtube.com/watch?v=aDPW7a0leU8 — one accompaniment figure from beginning to end, the exact opposite of the four lines here.
For more lines running at once with an easier way in: Bach's Invention No. 1, BWV 772, already on this channel, is the two-line version: https://www.youtube.com/watch?v=Z5U-C-76ndk
