Playwright Luise Gottsched, née Kulmus, in 1732 wrote a letter to her future husband, the writer Johann Christoph Gottsched: 'The keyboard pieces sent over by Bach... are as difficult as they are beautiful. Even after playing them ten times, they still seem new to me.' A few years later polymath and Bach's former pupil Lorenz Christoph Mizler offered the following advice regarding these Clavier-Übung I partitas: 'Anyone who has difficulties with keyboard fingering will find it difficult to learn the keyboard pieces written by the famous Mr. Bach in Leipzig'. The name Sinfonia for the first movement in the Partita in C minor is redolent of opening cantata movements and the dotted rhythm of a French overture. The Grave adagio however, is not followed by the fugal fast section you would expect here. This approach was carried out more consistently and stylistically in the Partita in D major, although there the fast section approaches the form of a concerto. Instead, the Grave adagio of the Partita in C minor is followed by a sonata-like movement with an arabesque effect in the upper voice, followed by a lively fugato. As a result, the piece appears in three parts. In contrast, the opening Fantasia in the Partita in A minor is more akin to an invention, showing similarities with the opening section of the second English Suite of the same key. Moreover, since the 17th century, the distinction between the terms 'Praeludium' and 'Praeambulum' was insignificant. Yet Bach's delicately sculpted Praeludium in the B flat major Partita, is stylistically very different from the concerto-like Praeambulum of the Partita in G major. Lastly, the Toccata in the Partita in E minor offers rhapsodic-improvisatory sections framing a fugue after the style of Froberg, whose works for keyboard instruments must have been known to Bach.