Why is this a classic?

What categorizes  a book to be a classic? Is it the style of writing, or the person who writes it? I think for a book to be a classic the book has to have meaning and be unique. If a book is unprecedented and contains well written work then I consider it a classic. I gathered this be reading other books that were considered a classic. For instance, reading Shakespear's books. Shakespeare himself wrote many classic books. Shakespeare book are different than pretty much all the books i ever read. This is because of the way it was written. Its almost like a pom, he uses a special style of writing that no other author uses. His writing caught on, and everyone loved it. This is how it became a classic in my mind. Also, for a book to be a classic, it has to leave a lasting impression on the world. It has to last a long time. So in order for a book to be a classic it has to be acknowledged and loved by the readers, and it must be unique.