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 reused, but also how derivatives of the work may be licensed. The GPL thus effectively forbids proprietary or commercial adaptations of GPL-licensed code. The LGPL falls somewhere between, but still effectively permits commercial reuse via linking to an LGPL-licensed library. These three paradigms raise essential questions, such as whether or not attribution should be required, whether derivative works should be required to be licensed under similar terms, and whether commercial reuse of the licensed content ought to be allowed. These questions recur in open-content licensing even outside the software context. The issue is thus not whether to constrain users’ behavior, for all licenses constrain (even if only by maintaining extrinsic constraints imposed by copyright law), but rather which constraints a licensor finds best to effectuate her intent.

The same group of licenses might also be evaluated not for how they affect individual users, but for how they affect the commons. BSD-style licenses are essentially agnostic on the question of growing the commons. Developers may add software to the pool, but anyone else is free to incorporate the licensed content into a proprietary product and need not make their own contributions available for others to reuse. In contrast, the GPL’s reciprocity provision demands that what is borrowed from the commons be returned to the commons: modified versions of GPL-licensed software may be distributed only under the GPL (with source code) for universal copying and