The Sonata for flute and keyboard in E Flat ( BWV 1031) has been described as a composite work, maybe by Bach father and son. The 'Siciliano' movement from this work is a gentle, deeply meditative Pastorale, its subtle dance-metre recurring in a number of Arias by the elder composer including 'Erbarme Dich' from the St. Matthew Passion which is itself a variation on the first movement from the 4th. Violin Sonata ( BWV 1017).