Brain Pickings provides Calvino's 14 Definitions of What Makes a Classic:
1. The classics are those books about which you usually hear people saying: 'I'm rereading…', never 'I'm reading….'According to Calvino's rules, what are your classic texts? How did they move you? How does your classic text define you?
2. The classics are those books which constitute a treasured experience for those who have read and loved them; but they remain just as rich an experience for those who reserve the chance to read them for when they are in the best condition to enjoy them.
3. The classics are books which exercise a particular influence, both when they imprint themselves on our imagination as unforgettable, and when they hide in the layers of memory disguised as the individual's or the collective unconscious.
4. A classic is a book which with each rereading offers as much of a sense of discovery as the first reading.
5. A classic is a book which even when we read it for the first time gives the sense of rereading something we have read before.
6. A classic is a book which has never exhausted all it has to say to its readers.
7. The classics are those books which come to us bearing the aura of previous interpretations, and trailing behind them the traces they have left in the culture or cultures (or just in the languages and customs) through which they have passed.
8. A classic is a work which constantly generates a pulviscular [think pulverize] cloud of critical discourse around it, but which always shakes the particles off.
9. Classics are books which, the more we think we know them through hearsay, the more original, unexpected, and innovative we find them when we actually read them.
10. A classic is the term given to any book which comes to represent the whole universe, a book on a par with ancient talismans.
11.'Your' classic is a book to which you cannot remain indifferent, and which helps you define yourself in relation or even in opposition to it.
12. A classic is a work that comes before other classics; but those who have read other classics first immediately recognize its place in the genealogy of classic works.
13. A classic is a work which relegates the noise of the present to a background hum, which at the same time the classics cannot exist without.
14. A classic is a work which persists as a background noise even when a present that is totally incompatible with it holds sway.