Keyboard music circa 1780 is characterized by the simultaneous existence of a number of different styles. The galant style, inspired by the French intellect, took on its subjective animation from German "sentimentality" and, by way of integrating with the arioso and buffo elements of the Italian style, flowed into Mozartean classicism - a process which, above all, characterized the work of the sons of J. S. Bach. The multiplicity of styles in existence in the 1770s and 1780s did not only influence the actual composition of keyboard music, it also affected the construction of the instruments themselves. Harpsichord, fortepiano, clavichord, square piano and a strange hybrid like the so-called "tangential" clavichord all existed alongside each other. The allocation of instrument was left to individual good taste - always the ultimate arbiter in the 18th century.
The "Folia", also called "Les folies d’Espagne" since the 17th century, is a melodic model which has been used by many composers as a melodic and harmonic framework for the composition of variations. Carl Philipp Emanuel Bach wrote his twelve variations on the "Folies" in 1778. The opulence of the rhythmic, harmonic, dynamic and even polyphonic variation devices which Bach employs are without parallel for their time. Each of the twelve variations seems to be a quite individual, musically independent version of the basic theme, yet the impression of unbroken, cyclical unity is kept intact.
In about 1785, Emanuel’s younger brother Johann Christoph Friedrich Bach wrote a set of variations on the French song "Ah, vous dirai-je Maman", which was universally popular at the time. In contrast to the "Folies" variations, J. C. F. Bach’s work represents a less exacting variation model, intended for performance by the amateur music-lover. In the fourteen pieces, most of which are written for two parts, the variations on the song melody are principally achieved by figurations to the upper part which conform throughout to a characteristic pattern. This cycle seems today to be a particularly delightful example of the art of late 18th century society.
Mozart’s D-major Rondo K. 485, which he wrote in 1787, and the C-major Sonata K. 545, which was composed a year later, both combine Italian cantabile with the inventiveness and sensitivity of C. P. E. Bach, whom Mozart revered all his life as one of his most important intellectual teachers. The D-major Rondo also documents the efforts of the classical composer to divest the rondo of its inherited character - that of an orderly progression - and to transform it by means of clever harmonic disposition, and a highly developed technique of thematic elaboration, into a self-contained cyclical form comparable with the sonata.
This is particularly true of the rondos from the compositions for "Kenner und Liebhaber" - connoisseurs and music-lovers - which were published by C. P. E. Bach from 1779 onwards. The Rondo in A from the second collection and the sonata following it exhibit the character of free fantasies; their restrained, elegiac mood seems to offer a presentiment of the Romantic era.
On October 17, 1777 Mozart wrote to his father from Augsburg, describing his visit to the organ and pianoforte maker, Johann André Stein, whose pianofortes he could hardly praise enough. These instruments, with which Mozart was so pleased and upon which he played with such great satisfaction, resemble more the harpsichord than the present-day modern piano. They are built entirely of wood, with extremely thin sound-boards and strings. From the exterior they are hardly distinguishable from harpsichords of the time. The strings are struck by small hammers; the hammers being about eight times smaller than those of the modern piano and covered with hard leather rather than felt. These differences in construction allow the "hammerclavier" of Mozart’s time a greater presence of overtones, thus a clearer sound as well as allowing for a greater rhythmic precision.
The pianoforte of the Mozart era has a much lighter touch than the modern instrument and requires a very different playing technique. It has two knee levers which are to be treated as "registers" or "stops"; one raising the dampers, the other moving a strip of cloth between the hammers and the strings (buff stop).
The musical style "for four hands" makes special use of all the different tonal effects which the instruments of the Mozart era offer. Mozart had already written pieces for two on one instrument as a child, although he is not the inventor of the style as his father Leopold had claimed. The Sonata in D, written in Salzburg at the age of 16 , is here performed on an early Mozart "hammerflügel" from the Stein-School; whereas the variations, composed 1786, are performed on an actual Stein instrument. Mozart sent the Sonata in C, a later work, to his friend, Gottfried von Jacquin, with the accompanying text "be so kind as to give this sonata to your sister - she should set about learning it as soon as possible, since it is rather difficult". It is here performed on a pianoforte which closely resembles Mozart’s own instrument, built by Anton Walter in Vienna.
Johann Abraham Peter Schulz, to whom we owe the musical setting of "Der Mond ist aufgegangen" by Matthias Claudius, is best known for his "Lieder im Volkston" (folk songs), which where published in three volumes between 1782 and 1790. In a biographical sketch of Schulz which appeared in the musical journal "Allgemeine Musikalische Zeitung" immediately after the composer’s death, Johann Friedrich Reichardt recalls how he and Schulz adhered faithfully to the prescribed rules of sonata form in their piano writing in the 1770s. "How often we laughed later over our conventional belief in the musical forms sanctified by the Berlin School! When I had played my sonata to Schulz as far as the first section of the last movement, he said ’Now all we need is a good modulation in a related minor key and then a successful return to the main key for repetition of the best passages in the first section, and voilà! - the sonata is comme il faut.' "  The Allegretto in A-minor, the fifth of Schulz’ "Sechs Klavierstücke" Op. 1 (1776), is one of the same sonata movements comme il faur which the composer and Reichardt were subsequently to smile at in ridicule of their earlier efforts. But we should not take Schulz’ verdict on a style of composition of which he was previously an ardent follower too seriously, but should rather note his touchiness where any kind of schematic composition was concerned.
"Truthfulness and moving simplicity", which Reichardt points to as Schulz’ noblest artistic virtues, also serve to characterize the Allegretto in A-minor, a piece which shows the influence of C. P. E. Bach in both form and expressive content. Only that everything is somewhat simpler than what we are used to from the harpsichordist of Frederick the Great, more for the bourgeois amateur than the virtuoso player.
Composing fugues seemed to the advocates of the new "sensitive" style, post-1735, to be "outmoded pedantry". Music ought to be "a real outpouring of emotion" and not just "fugal noises". Wilhelm Friedemann Bach, the eldest son of Johann Sebastian, followed a third course of action in his eight three-part Fugues, which he dedicated in 1782 to Princess Anna Amalie of Prussia, the musically gifted sister of Frederick the Great: he emotionalized the fugue. We possibly owe this experiment, which many people must have found paradoxical, to a characteristic of W. F. Bach’s; as Carl Friedrich Zelter put it, in a letter to Goethe, "As a composer, he liked to be original at all costs." It seems more likely, though, that Bach was consciously continuing a development initiated by his father, which is particularly noticeable in the second part of "The Well-Tempered Clavier" (1742) and in "The Art of Fugue" (1749/ 50) - namely, the individualisation and increasing characterisation of the fugue.
Obviously, the attempt to expand a contrapuntally bound genre such as the fugue so that, like sonata movements, rondos and "fantasies", it had the power to "speak" and "move" the listener, required certain relaxations of its strict formal structure. In W. F. Bach’s case these amount to the abandonment of the independent obbligato counter-subject, the renunciation of a schematically determined ordering of notes and parts, and the opening out of the intermezzi into autonomous, contrasting sections of the music. In spite of these basic features being common to all eight fugues in the set, Bach presents us in each one with a new reconciliation of emotional expression and fugal form. The Fugue VIII in F-minor is particularly remarkable: its status as a masterpiece was recognised by Mozart, who arranged the work for strings (his K. 404 a). The eighth fugue is also the one which does the most handsome justice to W. F. Bach’s concept of a fugue saturated with sentiment. The structural requirements of fugue form are fulfilled by a chromatically descending subject, which returns, tightly-woven, in the second half of the piece. Exceeding all conventional bounds, Bach links contrasting, freely expressive sections to the fugal subject to achieve a quite unprecedente overall effect.
It took a long time for Johann Christian Bach’s place in musical history to be recognised. The nineteenth century regarded this youngest son of J. S. Bach as an apostate who had turned his back on solid musical craftsmanship and had yielded to the lures and fashions of the wide world. Only since the beginning of the twentieth century has he commanded respect as one of the creators of the sentimental-galant instrumental style, a style which marked the transition from the high Baroque to Viennese classicism, and, with its aesthetics of conscious simplicity and direct expressiveness, founded a new musical ideal. Mozart was more than briefly influenced in his youth by the "Milan" or "London" Bach, and retained a lifelong regard for him which was shared by few of his contemporaries.
J. C. Bach’s piano music is both graceful and full of moderation: it never drifts off into superficiality, nor into deep passion. The six sonatas of each of the two sets for unaccompanied clavier, op. V (published 1768) and op. XVII (ca. 1779) are intended for either harpsichord or fortepiano, as was the custom at the time; the music, however, gives the impression that Bach had in mind the modern instrument, which, with its rich tonal nuances, lends itself better to dynamic contrast. The frequent Alberti basses and the abundant arpeggios also suggest the fortepiano as the most suitable instrument. In formal terms, these keybord sonatas exemplify what was, at the time, still a fairly new genre at an advanced stage of development. Although Bach’s music is anything but immature, the fluctuating number of movements in the works (sometimes two, sometimes three) and the varying form of the finales show that the piano sonata had not yet established itself as a musical form. The subjects of the main movements of the sonatas contrast distinctly with one another, but the development remains rudimentary. The elegant, graceful writing and the bel canto melodies derive from Italian music, and the sonatas do not require a brilliant virtuoso: in fact, Bach’s contemporary Charles Burney claimed, with a degree of exaggeration, that they could be performed "by ladies without too much trouble". They do, however, demand a pianist capable of sensitive, eloquent playing. In a work like the B-major sonata, op. 17/ 6, only a truly sensitive pianist will be able to realise the restrained, almost rapturous expression, and the sensuous cantabile, so lyrical in the slow movement, that so fascinated the young Mozart.
Mozart’s D-minor piano piece K. 397 is one of a handful of works in which Mozart enters into the realms of fantasy. They are the fruits of a period, beginning early in 1782, during which Mozart devoted himself to intensive study of the works of Bach and Handel, and of their North German successors, above all the master of free fantasy-form, C. P. E. Bach. The work is clearly divided into three parts: a brief introductory Andante made up of arpeggio chords, almost improvisational in character, is followed by two sharply contrasting melodic sections, a plaintive Adagio, whose melancholy is not to be banished, not even by wild presto runs over the whole keyboard, and a charming, serene Allegretto in the major, rounded off by a short cadenza, which releases the tension built up in the first two movements. The unrestrained rhapsody of the work is not an end in itself, but rather, in its permeation of the music’s recurringly rigid lyrical structure, gives impulse to a gradual process of mental relaxation. Thus the piece which seems at first sight so unpretentious, even aphoristic, requires a performance of great delicacy and a tender, expressive tone such as is only offered by fortepianos built in southern Germany and Austria with the so-called "Viennese action".