Nothing is art unless its design function is
(a) being a source of knowledge about the thing copied, and
(b) serving as a stimulus of the feelings ordinarily provoked by the thing copied.
1. What the theory says seems to be true of all the things people used to categorize as art; there used to be no examples of things that were art but were not in some way copies of something.
2. The theory fits what people used to learn to do when they learned to be artists.
3. The theory fits what people used to value about art; it makes sense of how people used to judge and evaluate art and artist.
4. The theory enables us to make sense of the distinction people used to make in their everyday activities between what is art and what is not art, and between who is an artist and who is not an artist, and between what is good art and what is not good art.
5. The theory used to increase people's systematic understanding of the world.
6. There used to be no alternative theories we know of for which all of the above were true.