- Ich sage ihnen vor Gott, als ein ehrlicher Mann, ihr Sohn ist der größte Componist, den ich von Person und den Nahmen nach kenne: er hat geschmack, und über das die größte Compositionswissenschaft.
- Before God and as an honest man I tell you that your son is the greatest composer known to me either in person or by name: He has taste, and, furthermore, the most profound knowledge of composition.
- If I could only impress on the soul of every friend of music, and on high personages in particular, how inimitable are Mozart's works, how profound, how musically intelligent, how extraordinarily sensitive! (for this is how I understand them, how I feel them) — why then the nations would vie with each other to possess such a jewel within their frontiers. Prague should hold him fast — but should reward him, too: for without this, the history of great geniuses is sad indeed, and gives but little encouragement to posterity to further exertions; and unfortunately this is why so many promising intellects fall by the wayside.
- Letter to Franz Rott (December 1787), from The collected correspondence, and London notebooks of Joseph Haydn, ed. H.C. Robbins Landon (1959), p. 73