This collection of eighteen short preludes with corresponding fughettas is a mixture of Bach's Small (Short) Fugues preceeded by Bach's Small (Short) Preludes, as well as the insertion of six fughettas composed by his son W.F. Bach. The editor's plan was to produce a "Preparatory to the Well-Tempered Klavier". To achieve this end, he also transposed three of the preludes to different keys in order to adapt them to the fugues to which they are united.