Rosenthal acquired the inspiration for his picture from a comment which Bach had made in a letter to a friend of his, Georg Erdmann, dated 28 October, 1730, announcing, “Of my first marriage, three sons and a daughter are living [Wilhelm Friedemann, age 19; Carl Philipp Emanuel, age 16; Johann Gottfried Bernhard, age 15; and Katarina Dorothea, age 21]…. Of my second marriage, one son and two daughters are living [Gottfried Heinrich, age 6, Elisabeth Juliane Friederike, age 4; and Regine Johanna, age 2]…. the children of my second marriage are still little, the eldest, a boy being six years old. They are all born musicians, and I can assure you that I can already form a concert [consort, ensemble], both vocal and instrumental, of my own family” (Philipp Spitta, Johann Sebastian Bach, translators Clara Bell and J. A. Fuller-Maitland [Dover Publications, Inc.: New York, 1992], II, page 254. In regards to the names of his children, see volume II, pages 8 & 153; and volume III, pages 268 & 350f.! Likewise, consult Christoph Wolff, Johann Sebastian Bach, the learned musician [W. W. Norton & Company: New York, 2000], pages 396-398!

Based on this information, Rosenthal actually painted an extra boy into his picture that did not exist at that time.

Incidentally, “Sebastian” actually was Bach’s first name, that is, it was the name by which his wife and others called him. In other words, according to common practice among the Germans at that time and later, the first listed name(s) (for example, “Johann”) was the middle name, while the name (“Sebastian”) which came right before the last name (“Bach”) was actually the first name.