The New York Times has an interesting story on a copyright case involving a possible sequel to The Catcher in the Rye:

The judge, Deborah A. Batts of United States District Court in Manhattan, granted a 10-day temporary restraining order forbidding publication in the United States of a new book by a Swedish author that contains a 76-year-old version of Holden Caulfield while she considers arguments in a copyright-infringement case filed by Mr. Salinger.

His lawyers contend that the new work is too derivative and that the characters in "Catcher" are protected by copyright. . . .

"I'll issue a written decision as quickly as I can," she said, adding that until then, her order would prevent publication here of the new book, "60 Years Later: Coming Through the Rye," by J. D. California, a pseudonym for the Swedish writer, Fredrik Colting. . . .

Mr. Colting's book, which was published in England, describes itself as "An Unauthorized Fictional Examination of the Relationship Between J. D. Salinger and his Most Famous Character." His American lawyer, Edward Rosenthal, called the book a critique that describes an aged Holden Caulfield — in the persona of a character called Mr. C — as "a lonely old man," and depicts Mr. Salinger as a prisoner of his own achievements who is haunted by his famous creation.

Characters in Mr. Colting's book and Mr. Salinger's inhabit parallel worlds, visiting Grand Central Terminal, the Museum of Natural History and the carousel in Central Park. Both Holden Caulfield and Mr. C despise the word "grand" and both like the phrase "to tell you the truth."

Supporting characters from "The Catcher in the Rye" also surface in Mr. Colting's book. There are references to Mr. Spencer, a teacher from Pencey Prep, and to a student, Stradlater, who in the new book confesses to having stolen a pair of gloves that Holden Caulfield wondered about in Mr. Salinger's book.

Holden Caulfield's younger sister, Phoebe, shows up in the book by Mr. Colting too, having aged into a drug user suffering from dementia.

Mr. Rosenthal argued that his client's book, which includes several new characters, qualified as a form of literary criticism because it provoked questions about the nature of Mr. Salinger's book. "I believe that this work significantly comments on 'Catcher in the Rye,' " he told the judge.

But Marcia Paul, a lawyer for Mr. Salinger, said the book has assumed the appearance of a sequel.

While all this sounds bad for the author of the new work, there was one line of argument offered by Salinger's lawyers that seems off base, even though it might or might not be supported by case law:

Mr. Salinger's lawyers have said that Mr. Colting is trying to exploit the popularity of "The Catcher in the Rye," a classic coming-of-age novel that has sold 35 million copies . . . .

"They described and sold this book," she said, "in order to trade on 'Catcher in the Rye.' "

It is absolutely routine for one work to spawn imitators that "trade on" or "exploit the popularity" of the more successful work. Very successful works create their own subgenres.

And books, movies, plays, and TV shows are often referred to or marketed as being attractive to those who liked an earlier work. I did a quick Westlaw news search for the phrases "Star Wars meets" or "meets Star Wars" and found 461 examples, such as "'Star Wars' meets 'The Ten Commandments'" or "Monty-Python-meets-'Star-Wars.'"

In a Westlaw search, I found 252 examples of "'Jaws' meets" or "meets Jaws."

There were 62 examples of "from the studio that brought you" and 21 examples of "from the producers who brought you."

Though most of these examples of trading on another work's success were made by third-party commentators, some were made by marketers of the new works.

I understand why the law of copyright might want to restrict the writing of actual sequels or prequels using the same characters. I offer no argument on that issue, though I would want to give a broader protection for commentary in novel form on earlier works than current law probably affords for modern works (e.g., I think that the many reinterpretations of Sherlock Holmes are a pleasant and useful addition to modern literature).

My comments here are not really about existing copyright law, which is not one of my areas of expertise. Rather, it is about where, in my opinion, the law should draw the line. If in J.D. California's novel no characters had been repeated, I would see nothing wrong with the rest of what is complained of. Building on other people's accomplishments and appealing to existing fans of copyrighted and trademarked work is how knowledge, art, and commerce advance.