Friedrich Ludwig Dülon
Thereafter he was asked by my father to conduct the same test with me in which I had done so badly with Kirnberger. Because I had now already gone more deeply into the area of theory, the good Bach could not succeed in confusing me, even though there is no doubt that he had as much musical sophistry at his command as Kirnberger; … No matter how often he rested on a tonic chord and asked me in which key he was, I gave him the right answer every time, without even needing to reflect first.
…, how are you at composition?’
“Herr Kapellmeister (C P E Bach),” replied my father, “here a kind of deception could easily take place since my son could dictate to my quill a piece which he has learned by heart. In order to prevent this, I must ask you to give him a theme, for instance for a solo allegro.” Bach did that immediately; I took the flute in hand, repeated the theme, improvised something on it, then laid my instrument aside again and dictated to my father the theme and the first part of the whole piece. When it was complete Bach looked it over, found it right, turned suddenly to my father, and broke out with the following words: “You have in fact often told me that your son could compose; but don’t hold it against me that I did not believe you; now this test has convinced me.”