Liszt's ground-breaking Fantasia and fugue on Ad nos, ad salutarem undam, completed in 1850, was his first major work for the organ and his first known organ composition of any kind. Some five years later it was followed by the much shorter Prelude and fugue on B.A.C.H., which was commissioned for the opening of the organ (re)built by Friedrich Ladegast for Merseburg Cathedral between 1853 and 1855, then the largest organ in Europe. Liszt, however, was unable to finish B.A.C.H. in time, and so Alexander Winterberger, the cathedral organist and Liszt's pupil, opened the new organ with the Ad nos fantasia instead.

Liszt based many of his works on well-known themes, sometimes from tradition but more often by other composers. Even in such works as Am Grabe Richard Wagners satirization was never in Liszt's mind, however, rather the writing of serious tributes, although his direct quotations from those such as Mozart, Arcadelt, Chopin and Lassus became cuckoo-like on occasion. Ad nos falls between these categories, since it borrows a melodic framework rather than an actual theme. Ad nos, and its cousin for the piano, Illustrations du Prophète also written in 1850, became significant for Liszt, not only preparing the way for the B Minor Sonata of 1853 but also for cycles such as the monumental Opern-Phantasies, the piano arrangements from Wagner's operas.

In the case of Ad nos, Liszt sought the permission of Meyerbeer, then the most important of the Paris opera composers, to use the song of the anabaptists from his opera Le Prophète. While today all this may be considered plagiarism, Meyerbeer was delighted, writing to Liszt: I cannot express how happy I am that you have found one of my songs fit to use in one of your piano compositions. … Several critics are saying that a number of my chorus-themes are contemporary with Luther himself – I cannot be bothered to disillusion them! Meyerbeer's theme is a jaunty tune in nine-eight time, but Liszt adapts it in many magisterial ways, never using it in its original form.

The implication of Meyerbeer's letter is that Liszt's first intention was to write a fantasia for piano on Ad nos, but there was an increasing interest in organ-piano hybrids at the time, and Liszt himself possessed a piano-orgue by the maker Alexandre. Schumann had just completed his works for 'orgel oder pedalflügel', Cavaillé-Coll was developing the extraordinary Poïkilorgue, and there was much interest in the expansion and development of the harmonium otherwise.

Liszt, moreover, was then resident in Weimar, where he was surrounded by the inheritance and legacy of Bach, and the organ of Merseburg, renowned for centuries, crystallised his devotion to his 'second instrument'. Liszt was initially guided towards the organ by his organist pupil Alexander Wilhelm Gottschalg, but it was most probably Alexander Winterberger himself who finally caused Liszt to compose Ad nos for the organ. For the first edition, published by Härtel, Liszt included two versions, one for organ or pedal-piano and another for piano duet.

With these grand transcendental variations, a completely unprecedented form of organ writing was established. Ad nos is not only on a larger scale than anything that had preceded it, but also makes use of the organ in a symphonic style that no one had previously imagined. Mendelssohn's sonatas may have influenced Liszt, but these were classical, seldom venturing near the dramatic territory of Beethoven, and it was essentially Liszt's transference of piano virtuosity to the organ that revolutionized the approach to the instrument.

Formally, Ad nos is in three linked movements. Each is preceded by an introductory passage. A brief recitative prepares the way for the adagio, and a succinct but virtuoso cadenza in broken octaves is interpolated before the fugue. The debt to Bach's Toccata, adagio and fugue in C, BWV 564, and the three-movement eighteenth-century piano sonata remains clear, however, while Liszt's use of variation technique revolves around the 'transformation of themes' that was absolutely his own. In this way, each movement adapts Meyerbeer's theme for an heroic fantasy, a lyrical set of variations on the song-transformation, and the driving fugue, respectively. Not usually given to writing fugues, Liszt had learnt much from his piano transcriptions during the 1840s of six of Bach's 'Great' Organ Preludes and Fugues, BWV 543-548. Otherwise, two further transformations of Meyerbeer's theme enable the fugue and the improvisatory cadenza-like coda that grows out of it, but the final page sees a triumphal statement of the theme as a resplendent chorale, its character distantly removed from that of Meyerbeer's original melody.

If Liszt virtually threw the organ out of the church and onto the concert platform, Mendelssohn tended to merge the idiom of the salon with that of the church. Nowhere is this more apparent than in the separate Allegro in B flat of 1844. Perhaps, in creating its song-without-words style Mendelssohn followed the mood of his Romances sans paroles too closely for comfort, or at least the comfort of the Victorian church, and it may have been for this reason that he excluded the movement from the fourth Sonata, firmly rooted in the same key and assembled at the same time. When Mendelssohn collected the movements of this Sonata together, moreover, he repressed the Andante alla marcia as recorded here, rewriting it as a more dimly-lit Andante religioso. The other movements of the fourth Sonata were probably later additions, but the central fugue of the finale certainly began its life in the form heard here. In incorporating the pedal scale in the fugue-subject of this version, Mendelssohn only came to realise later that the difficulties for many potential church organist performers might be forbidding. He therefore altered the scale-passage to a more straightforward alternate-foot broken-chord figure. There can be no doubt that Mendelssohn's first thoughts for the finale of the fourth Sonata were in this version of the Fugue, although some speculation is involved in the joining of the three movements recorded here: while obviously seminal, it is most unlikely that Mendelssohn could have intended this trilogy as any kind of original version of the fourth Sonata. Be that as it may, they nonetheless form a charming and highly characteristic suite of three pieces that may be seen to constitute a valid alternative to the fourth Sonata itself.

Brahms was even less of an organist than either Liszt or Mendelssohn, but this notwithstanding, he always valued his Fugue in A flat Minor very highly. This elevated miniature is seldom heard on account of its contrapuntal complexity and the extremely remote keys through which it passes. Brahms's extraordinary fluency allows him to weave the chromaticism through D flat Minor, C flat Minor and E flat Minor in an unforced and perfectly natural way. Marked trübe (grey and overcast) there are moments of hope that the sky will clear, but at the end yearning and resignation remain. Initially composed shortly after the death of Schumann in 1856, and during the same period as the ill-fated first Piano Concerto, Brahms presented a copy of his first version of the Fugue in A flat Minor to Clara Schumann on her late husband's birthday. The revised and final version was then published at Brahms's behest in the Allgemeine Musikalische Zeitung in 1864. The sighing phrases of its subject and the sadness of the final cadence confirm that it was certainly conceived as a memorial to Schumann.

When Clara Schumann herself died in 1896, Brahms was so profoundly affected that he never really recovered. They bear no dedication, but nonetheless it may be inferred that the Elf Choralvorspiele (Op.122), composed at Ischl, Upper Austria, during the last days of Brahms's life, were written in Clara's memory. Herzlich tut mich verlangen, the second of two settings of the Passion chorale in Op. 122, conveys a mood at once restless and elegiac. The final cadence with its unexpected tierce de Picardie settles on a note of optimism, however: a recaptured moment of Clara's lively spirit perhaps? Or even a desperate hope that he may yet see her again…?

Reger recreated Bach's monumental Baroque through the prism of Brahms, wrote Reger-biographer H. Wirth in 1974. Bavarian-born Reger is renowned for having written organ works in an attempt to defeat his friend and contemporary, the organist Karl Straube. Straube's legendary technique caused many to marvel, and Reger set about trying to produce compositions that Straube would find too difficult to perform. As far as can be determined, he never succeeded, but Reger's works thus became formidably demanding and complex. Reger wrote most of his colossus chorale-fantasias – there are seven of them – at Weiden between 1899 and 1901. These include the two that form his Op. 40: Wie schön leucht' uns der Morgenstern (How brightly shines the morning star) and Straf mich nicht in deinem Zorn (Rebuke me not in thine anger), and the three of Op. 53: Wachet auf! ruft uns die Stimme (Awake! a herald voice is calling), Alle Menschen müssen sterben (All mankind must die) and Hallelujah! Gott zu loben (Hallelujah, God be praised!). In its first printing Wie schön leucht' uns der Morgenstern bore a dedication to F. Spitta but this was later repressed as the work was initially intended for Straube, to whom the first manuscript was sent. Straube moved from Wesel to Leipzig in 1902 partly because of his acquaintance with Reger.

Together with the generic and contrapuntal links with Bach, and more specifically the Fantasia and fugue in G Minor, BWV 542, the influence of Liszt's symphonic poems was fundamental, although a continuous flow of chromatic, quasi-improvisatory material inspired by the words of the choral texts was Reger's core principle that looked retrospectively to Bach again, and rejected any concept of programmatic 'time-lines'.

With Hallelujah! Gott zu loben and Wie schön leucht' uns der Morgenstern, and to a lesser degree with the other chorale-fantasias, a more direct influence can be seen. Heinrich Reimann's fantasia on Wie schön leucht' uns der Morgenstern composed in 1895 became a model for Reger, in fact. Reimann, teacher of Straube, was organist of the Kaiser-Wilhelm-Gedächtniskirche in Berlin, and Reger's admiration of Reimann's music is partly borne out in Wie schön leucht', which uses Reimann's fantasy as a basis, formally, architecturally, texturally and in many aspects of its stylistic approach. The treatment of verse three (Pour thyself into the depths of my heart, my only Lord and God) as an ornamental Baroque setting by both composers is so similar that Reger might appear to lack originality, although Straube himself suggested that Reger follow Reimann's example for this verse. The ensuing build-up is skillfully handled by Reger, while the lesser Reimann submits to a sectional approach. Reimann's introduction is also a pale reflection of the later, quasi-cataclysmic introduction of Reger. Leading to the first verse that mirrors merely the gentlest starlight and meditates on the 'sweet stem of Jesse' idea, Reger's verse two then sets out to achieve pearl-like effects ('Be thou my pearl, thou precious king') through texture and registration. Quite a lot of the text is omitted by Reimann, but Reger includes it all. Verse three is the Bach-inspired ornamental elaboration, a true Reger adagio, in which choral-generated continuous melodic garlands are harmonically transported to each new phrase by the background of an ever-flowing, now gentle chromatic accompaniment. The form of this verse may not have been Reger's original intention, but it nonetheless serves to illustrate the 'glowing jasper stone, precious jewel' allusion to the grace of Christ.

Verse four ('From God I receive the brightness of joy') introduces brilliant demi-semiquavers above the chorale in the pedal, but the elation subsides for the 'He is my shadow' section. Some have considered this formally disadvantageous, but these six bars very soon lead to the fantasia's whirling conclusion, più vivacissimo: 'ever shall my heart praise God.’

The organ is then reduced rapidly and the fugue begins. The subject is closer to Bach's 'Great' G Minor than to Reimann, and it is the shortest such theme in the fantasias. There is no regular counter-subject, although in the background there is a recurring waning line that descends chromatically through the interval of a minor seventh. This can be seen to relate to the octave descent of the final line of the choral melody, but Reger's main point of interest is the development of the first three notes of the fugue, which are transformed from their initially perfunctory anacrusic role into chords of 'joyful praise'. 'Let the sweet strings sound, and the song of praise' prompts the arrival of the chorale in the pedal. Derived from the Baroque cantus firmus im pedal, the introduction of the chorale in majesty in this way became one of the remarkable strengths of Reger's fantasias. Here the symbolized text tells of the correspondence between the joy of hearing the music of praise and the triumphal rejoicing that will be found through joining Christ in eternity. 'Sing, rejoice, give thanks: for great is the glorious king of all the earth.' So Reger concludes with final bars of intense force, and a representation of the dazzling brilliance of the morning star.