The latest edition of Clarkesworld Magazine contains an article titled "Something Greater: An Epic Discussion of Epic Fantasy, part 1."
They have gathered 28 pros (26 authors, 1 editor, and one literary agent) to discuss one of the most popular sub-genres on the market. Taking part are: Steven Erikson, Terry Brooks, Kate Elliott, Peter Orullian, Gaie Sebold, Erin Hoffman, Lou Anders, James Barclay, Elizabeth Bear, Trudi Canavan, Rowena Cory Daniells, David Anthony Durham, Ian Cameron Esslemont, Lynn Flewelling, Ed Greenwood, John Jarrold, N. K. Jemisin, K. V. Johansen, J. V. Jones, Paul Kearney, Juliet McKenna, Robin McKinley, Robert V. S. Redick, Patrick Rothfuss, Brandon Sanderson, Michael A. Stackpole, Victoria Strauss, and Gav Thorpe.
In the first part of this enormous interview, they answer three questions: What is at the heart (or core) of Epic Fantasy? Why do you write Epic Fantasy? What is the relationship between characters and settings in Epic Fantasy?
Here's Patrick Rothfuss' answer to the first question:
It depends on who you ask, really. In my opinion, Epic Fantasy is one of the most vaguely-defined genres out there.
It's sort of like "pornography" or "art." Most everyone uses those terms very loosely, and they don't really have a definition for them. They operate under a policy of "I know what it is when I see it."
With Epic Fantasy, the real question is what part of the story is supposed to be epic? The action? The length of time depicted? The length of the actual books?
I've heard some people say that the difference is the detail involved in the description of the world. But that seems like a pretty weak defining characteristic to me. If that were the case, most science fiction would be epic. But people don't think of it that way.
I don't claim to know, myself. But I think the rule of thumb most people use is the length of the books. If a book is more than 500 pages long, most people call it Epic Fantasy.
The second part will be found in the next edition of Clarkesworld Magazine.