Institutio Oratoria

As for sculpture, its activity extends to wood, ivory, marble, glass and precious stones in addition to the materials already mentioned.

And things which form the material for other artists, do not for that reason cease forthwith to be material for rhetoric. For if I ask what is the material of the sculptor, I shall be told bronze; and if I ask what is the material of the maker of vessels (I refer to the craft styled χαλκευτική by the Greeks), the answer will again be bronze: and yet there is all the difference in the world between vessels and statues.

Similarly medicine will not cease to be an art, because, like the art of the gymnast, it prescribes rubbing with oil and exercise, or because it deals with diet like the art of cookery.