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 to answer a set of three yes-or-no questions, two combinations are off the table because an author cannot choose both “No Derivatives” (derivative works are forbidden) and “Share Alike” (derivative works are permitted so long as they are distributed under the same license terms). The remaining six possible combinations, accordingly, describe the basic family of Creative Commons licenses from which creators may choose: (1) Attribution only (BY); (2) Attribution-Share Alike (BY-SA); (3) Attribution-No Derivatives (BY-ND); (4) Attribution-Non-Commercial (BY-NC); (5) Attribution-Non-Commercial-Share Alike (BY-NC-SA); and (6) Attribution-Non-Commercial-No Derivatives (BY-NC-ND). Web sites, photographs, instructional materials, scholarly research, comic strips, maps, sound recordings, motion pictures, and many other works—numbering in the hundreds of millions —have been published under Creative Commons licenses.

All six of the standard Creative Commons licenses permit users to copy and distribute the licensed works, although the three “NC” licenses disallow copying and distribution for commercial purposes. Four of the licenses (all except the two “ND” variants) also permit users to create and distribute modified works based on the licensed content, although the two “NC” variants again restrict commercial uses, and the two “SA” variants require retransmission of the same set of licensed freedoms to users of any such derivative works. The combined effect of all these alternatives is to give the licensor fine-grained control over the various policy decisions implicated in the other open-content licensing arrangements discussed above. Whether to allow derivative works, whether to require licensing reciprocity, whether to