The subtitle of the work, commonly referred to as “The Wedge”, refers to the first half of the fugue subject, which opens up as a sort of widening, chromatic wedge around the tonic point. The tradition of descending chromatic fourths in Bach's E minor fugue subjects include the BWV 914 harpsichord Toccata, the BWV 855 Prelude and Fugue from the Well Tempered Clavier, Book 1, as well as the “Un poco Allegro” movement from the BWV 528 Organ Sonata. The fugue, clocking at 231 measures, is among Bach's longest and most elaborate organ fugues. The movement is unique in that it is in a three-part structure, with the third da capo section being a note-for-note reprise of the first. The second section suddenly thrusts the piece into an over-one-hundred measure episode of rapid, toccata-like passages of great virtuosity, with the cascading passagework occasionally giving way to the subject.

Albert Schweitzer described both movements as being “so mighty in design, and have so much harshness blended with their power, that the hearer can only grasp them after several hearings.” Philipp Spitta referred to the work as a “two-movement symphony”, commenting on the work's “life energy” and the “extreme daring” nature of the fugue subject. Peter Williams attributed the work's “riveting power” to the “easily felt balance between the two movements.”

https://www.youtube.com/watch?v=INKRUAEVRi0

Double and triple fugues, employing two and three subjects respectively:

• Contrapunctus 8, a 3: triple fugue with three subjects, having independent expositions
• Contrapunctus 9, a 4, alla Duodecima: double fugue, with two subjects occurring dependently and in invertible counterpoint at the twelfth
• Contrapunctus 10, a 4, alla Decima: double fugue, with two subjects occurring dependently and in invertible counterpoint at the tenth
• Contrapunctus 11, a 4: triple fugue, employing the three subjects of Contrapunctus 8 in inversion

https://en.wikipedia.org/wiki/The_Art_of_Fugue

(incipit from Edition Peters Nr. 218)	[page] title in first edition other description
	[1] Contrapunctus 1 Fuga simplex rectus Simple fugue (one subject)
	[3] Contrapunctus 2 Fuga plagalis Simple fugue, ends on V (in autograph)
	[6] Contrapunctus 3 Fuga simplex inversus Simple fugue, inverted
	[8] Contrapunctus 4 Fuga simplex inversus Simple fugue, inverted
	[13] Contrapunctus 5 Counter-fugue - fuga inversa Stretto fugue
	[16] Contrapunctus 6 a 4 in Stylo Francese Fuga inversa Stretto fugue with augmentation and diminution
	[19] Contrapunctus 7 a 4 per Augment et Diminut Fuga inversa Stretto fugue with augmentation and diminution
	[21] Contrapunctus 8 a 3 Fuga a tre Soggetti Triple fugue (3 subjects)
	[26] Contrapunctus 9 a 4 alla Duodecima Fuga rectus with obbligato countersubjects Double fugue (two subjects)
	[29] Contrapunctus 10 a 4 alla Decima Double fugue (two subjects)
	[45] Contrap a 4 Fuga inversus with two obbligato countersubjects all Decima (variant of Contrapunctus 10)
	[32] Contrapunctus 11 a 4 Fuga a quattro soggetti a 4 Triple (quadruple) fugue
	[61] Fuga a 3 Soggetti Triple fugue (unfinished; possibly planned to be quadruple)
	[39] Contrapunctus inversus a 4 Mirror fugue in contrappunto simplici a 4 rectus
	[37] Contrapunctus inversus 12 a 4 Mirror fugue in contrappunto simplici a 4 inversus
	[41] Contrapunctus a 3 Mirror fuga inversa in contrappunt duplici a 3 inversus
	[59] Alio modo Fuga a 2 Clav (variant of Contrapunctus a 3 for two keyboards)
	[43] Contrapunctus inversus a 3 Mirror fuga inversa in contrappunt duplici a 3 rectus
	[57] Fuga a 2 Clav (variant of Contrapunctus inversus a 3 for two keyboards)
	[48] Canon per Augmentationem in contrario motu Canon I
	[51] Canon alla Ottava Canon in Hypodiapason Canon II
	[53] Canon alla Decima Contrapunto alla Terza Canon III
	[55] Canon alla Duodecima in Contrapunto alla Quinta Canon IV

http://www.musanim.com/ArtOfFugue

How does a pipe organ actually work? | Anna Lapwood | Classic FM

0:32 Ravel - Le Tombeau de Couperin 
3:26 Fugue in G-minor BWV 578
5:50 Prelude & Fugue in A Minor BWV 543

Pipe Organ (An instrument the size of a building)

The Great Stalacpipe Organ (a cave that you play)

Fugue improvisation for beginners

How to learn Bach Fugues on the piano- effective and useful methods

“some people jump out of airplanes, some deep ocean dive, we musicians sightread the fugues”

How to Learn Bach's Fugues

Beyond the Notes: BWV 543

最天真爛漫甜美的巴赫賦格

Fugue no. 21 – J. S. Bach //Musical analysis with structure

Fuga XXI

有好奇過地獄之門緩緩開啟是什麼聲音嗎

Jeanne Demessieux – Octaves

“Next to Jeanne Demessieux we all play the pedals like elephants!” (MARCEL DUPRE)

無法更滿意。這首樂章的地位想必不用多說。起初使我深刻的是僅僅是小提琴獨奏卻能二重奏甚至有一支樂隊的效果，意境深邃，樂理結構充滿數理的嚴謹慎密，感情有如宗教和哲學般直指人心、撼動靈魂。單純冠以好不好聽的評價無疑是低估了它的偉大、神聖和超越性。

再談這個版本。如果說演奏中沒有出現過技術上的差錯叫flawless，那Hilary Hahn這個版本在我心中從感情到技術都是perfect。沒有一點點紊亂地、忠實地還原了巴赫的初衷。開首就把那段極具挑戰性的多重和弦拉得飽滿而細膩，音色圓潤厚實，節奏不急不緩，在有那麼多橫跨四條弦的音符仍能保持從弓尾到弓尖一樣有力，充分顯示了她的功力深厚。少許具個人特色的演繹也是恰到好處，基調深沉卻不刻意煽情，不同部分之間的過渡流暢自然同時也不忘營造對比。尤其喜歡9分那裡，感情如急泉噴湧而出後的安詳寧靜一一像是映照著作曲者一生的苦難、掙扎、又像是睿智的長者對人生有了充分的感悟，一個虔誠的信徒在死亡將至時看見天堂溫暖的曙光。

另一個很喜歡的位置在13:30，好幾次在外面聽得熱淚盈眶。彷彿前面一層一層、無處安放的迴迂感情累積起來，終在這裡尋到了它的出口和答案，美麗得使人為之屏息。聽前面的部分心情隨著樂章跌宕起伏、為之動容，而後面就像被洗滌過一樣平靜，最後結局與開首互相呼應，悠長而完滿地收結，言有盡而意無窮。

總之是我在希望在喪禮上播的歌#1。

2016.06.27