Plagiarism is the quintessential literary sin, and lately it's been breaking out in the book world like a bad rash. The low point of 2006 came early, when Harvard undergraduate Kaavya Viswanathan's career went from bright young star to supernova in one month flat.

At the center of the latest scandal is Ian McEwan. The British press recently seethed with controversy surrounding his Booker-nominated 2001 novel, Atonement . McEwan had acknowledged in an author's note that his novel was inspired in places by Lucilla Andrews' 1977 memoir No Time for Romance. But when the Daily Mail set certain passages side-by-side, they turned out to be nearly identical. To McEwan's defense came the charge of the writer brigade. The Telegraph published letters of support from Martin Amis, John Updike, Colm Tóibín, Zadie Smith, Kazuo Ishiguro, Margaret Atwood, and Thomas Pynchon. All of them maintained that liberal methods of research are essential and healthy for the writing of historical fiction.

Thomas Pynchon's intervention — just one type-written page — came at an odd time, considering his own work is at the center of the season's strangest copyright showdown. Gravity's Rainbow Illustrated , the collection of artist Zak Smith's drawings for every page of the massive novel, was set to be published by Tin House in late December, until word of the project reached Penguin, Pynchon's publisher. Penguin 'convinced' Tin House to slap stickers on the already-printed books bearing a new, cripplingly awkward title: Pictures Showing What Happens on Each Page of Thomas Pynchon's Novel Gravity's Rainbow.

So what makes an adaptation a violation of copyright? Does it depend on what one steals, or perhaps even on who's doing the stealing? We asked Circuit Court Judge Richard Posner — author of the forthcoming Little Book of Plagiarism — to help us make sense of the charges flying around.

Boldtype: What is the difference between copyright infringement and plagiarism?

Judge Richard Posner: If there is actual copying, conscious or unconscious, of a copyrighted work, that is (with minor exceptions) infringement unless the copier has a license from the copyright holder. Plagiarism, however, is not a legal concept. If you copy a non-copyrighted work (maybe the copyright had expired) then you have not violated a law. But if you fail to acknowledge the copying, you may be branded a plagiarist, which will injure your reputation, perhaps irrevocably.

BT: What does copyright law protect when it comes to literature?

JRP: Generally, it protects only the form of expression, particular wordings, and unique characters. It does not protect familiar themes, plots, or genres.

BT: Looking at the evidence, did Ian McEwan violate copyright?

JRP: The issue in his case isn't copyright, but rather plagiarism. The question is whether he took so much from the earlier work that he could be said to have copied and therefore must acknowledge it. If so, was his acknowledgment adequate?

It seems like this one is between McEwan and his conscience, not the law. While copyright violation could land you in court, plagiarism is more likely to earn you infamy, or just dirty stares at parties.

-Toby Warner