BWV 26

Ach wie flüchtig, ach wie nichtig
BWV 26
Chorale cantata by J. S. Bach
Michael Franck, author of the hymn's text and melody
Occasion	24th Sunday after Trinity
Performed	19 November 1724 (1724-11-19)
Movements	6
Chorale	"Ach wie flüchtig, ach wie nichtig" by Michael Franck
Vocal	SATB choir and solo
Instrumental	horn flauto traverso 3 oboes 2 violins viola organ continuo

Ach wie flüchtig, ach wie nichtig (Ah, how fleeting, ah how insignificant),BWV 26, is a church cantata by Johann Sebastian Bach. He composed the chorale cantata in Leipzig for the 24th Sunday after Trinity and first performed it on 19 November 1724.

The cantata is based upon the hymn "Ach wie flüchtig, ach wie nichtig", versed and composed by Michael Franck in 1652. The tune was later edited by Johann Crüger. It is the only time Bach used this hymn, except BWV 644 (Orgelbüchlein). Its theme, the transience of human life, is the only connection to the prescribed gospel reading. The first and last stanza are used unchanged in both text and tune: the former is treated as a chorale fantasia, the latter as a four-part closing chorale. An unknown librettist paraphrased the inner stanzas as arias and recitatives. Bach scored the cantata for four vocal soloists, a four-part choir, and a Baroque instrumental ensemble of horn, flute, three oboes, strings and continuo.

Bach wrote the cantata in 1724 in his second year in Leipzig for the 24th Sunday after Trinity. That year, Bach composed a cycle of chorale cantatas, begun on the first Sunday after Trinity. The prescribed readings for the Sunday were from the Epistle to the Colossians, a prayer for the Colossians (), and from the Gospel of Matthew, the story of the Raising of Jairus' daughter (). The cantata is based on the hymn in 13 stanzas by Michael Franck (1652), to a melody by Johann Crüger (1661), "a meditation on the transience of human life and of all earthly goods". This aspect is the only connection to the gospel. An unknown poet retained the first and the last stanza unchanged as movements 1 and 6 of the cantata. He derived the inner movements as a sequence of alternating arias and recitatives from the inner stanzas.John Eliot Gardiner points out that "several of Bach's late Trinity season cantatas" concentrate on "the brevity of human life and the futility of earthly hopes".