Letters 87.13

We shall then reply: “You do not understand in what sense we have used the phrase ’that which is good in music.’ For we do not mean that which equips the musician, but that which makes the musician; you, however, are referring to the instruments of the art, and not to the art itself. If, however, anything in the art of music is good, that will in every case make the musician.”

Seneca, Letters to Lucilius 87.13, translated by Richard Mott Gummere