No one would confuse cyber-lawyer Lawrence Lessig with Homer Simpson – symbol for all that is dumb about America. But Lessig, a professor of law at Stanford University in Palo Alto, CA, has spent a good deal of time lately trying to figure out how to resolve a “doh!” moment of his own: realizing that the various intellectual property licenses that he helped design over recent years to encourage the sharing of intellectual property – a movement collectively known as “copyleft,” in contrast to copyright – may actually prevent it.

The problem is that the copyleft licenses, like the “free software” licenses from which they’re drawn, require that derivative works be licensed under identical terms. And those terms differ from license to license. So the collections (or “mash-ups”) of free text, audio, and video that Lessig and others have championed as the vanguard of a new “free culture” can’t combine works created under different licenses – even if all of the licenses are meant to encourage wide sharing. For example, text from Wikipedia, which uses a license called the Free Documentation License (FDL), could not be used as narration in a documentary film designed to be shared under a Creative Commons license.

In 2001, Lessig was one of the founders of Creative Commons, which was started to create flexible versions of copyright that would make it easier to share elements of creative works, such as text, video, and audio. The idea came out of the free software movement spearheaded by former MIT computer scientist Richard Stallman, who developed the free GNU operating system. Under Stallman’s definition, software is free if it can be modified and distributed freely. The best-known example of free software is Linux, a version of GNU that includes a core or “kernel” written by Linus Torvalds and his followers.

People who want to share their creative works under more flexible terms than those allowed with traditional copyright can now choose from six main versions of the Creative Commons license, ranging from the permissive “attribution only” license, which allows anyone to use your creation for any purpose, as long as you receive credit for it, to the “attribution noncommercial no derivative” license, which allows reuse, but not modifications or commercial use. Creative Commons also has several niche licenses covering things like audio sampling.

Although Creative Commons does not track how many writers, artists, and others are using its licenses, it does count “linkbacks” to its site – many of which come from the sites of writers, publishers, or artists using the group’s licenses. There are now 45 million such linkbacks, up more than tenfold from a year ago.

But the Creative Commons licenses are not the only copyleft licenses in widespread use. The FDL, used by Wikipedia and written by Stallman’s Free Software Foundation, differs from the Creative Commons not only in language but also in intent; it was designed primarily to protect manuals accompanying free software, and applies mainly to textual information.

Like the Creative Commons license, it requires that derivative works be distributed under the same terms – which can be burdensome even if one isn’t doing a mash-up. “If we had a photo on the site and you wanted to use it to make a postcard, you’d have to put the license on the back, and it runs eight pages,” says Jimmy Wales, co-founder of Wikipedia and chair of the board of Wikimedia in St. Petersburg, FL.

Wales expects that the compatibility problem will become larger as more video and audio is developed for sharing. Ultimately, says Lessig, the issue could lead to lawsuits over content misuse, particularly if a large institution, such as a university, were found to have violated license agreements by hosting or facilitating collaborations that mix licenses.

Right now, those are hypothetical problems, and the issues are more annoyances than potential torts. Lessig said that when he realized the problem, while speaking with Wales at a conference in Barcelona, Spain, last summer, “it was a Homer Simpson moment.” He said the issue took him back to the early days of mainframe computers, when machines built by IBM or Remington Rand couldn’t exchange data. And he says it’s happening now because legal culture is still stuck in the equivalent of the computer mainframe era. “We need to apply the principles of networks to law,” Lessig says.

That may be easier said than done. One part of the fix may be simple, says Eben Moglen, a professor at Columbia Law School and founder of the Software Freedom Law Center. “It’s comparatively easy to adjust the license language” to allow people to mix certain kinds of copyleft without compromising their original licenses, Moglen says. But without a common legal framework for all copyleft licenses, works that inadvertently mix licenses might become unshareable.

Creative Commons is working to address exactly that issue. Lessig says he expects to announce new language for appropriate Creative Commons licenses in January 2006, language that will allow one-way compatibility with the Free Documentation License – meaning people creating works under the FDL would be free to use Creative Commons-licensed content. (In this case, the relevant Creative Commons licenses needing modification are the “attribution by” and “attribution share-alike” licenses.)

Lessig says the language is currently circulating among Creative Commons advisers in draft form. Wales, meanwhile, is lobbying the Free Software Foundation to make accommodations in its language so that FDL-licensed content can be incorporated into Creative Common-licensed content.

Lessig and colleagues at Creative Commons are also trying to start a legal advisory board called CC: Lab, comprised of six to eight experts in licensing, who would become a standards body for copyleft licenses, giving guidance on how to structure licenses so that content meant to be shared can actually be shared. Lessig says Creative Commons will provide seed funding for the board, but he’s also looking for a grant over the longer term. He hopes to see this board launched in the spring of 2006.

Lessig thinks the design flaw in copyleft has been caught early enough that the license questions can be resolved before any major intellectual-property lawsuit crops up. However, he acknowledges that the issue is a tricky one . “It’s not easy to address, but it’s certainly possible,” he says. ”It will take some careful legal craft and some willingness on the part of people who have developed other free content licenses.”