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 the following clause (versions of which also appeared in GPLv1 and GPLv2) explaining the function of the license: “Developers that use the GNU GPL protect your rights with two steps: (1) assert copyright on the software, and (2) offer you this License giving you legal permission to copy, distribute and/or modify it.”

Every version of the GPL grants users of the licensed software the rights to engage in the otherwise-infringing acts of copying, modifying, and redistributing the licensed work. Like all open-content licenses, however, the GPL attaches conditions that limit the scope of the authorization the license confers. A licensee’s exercise of one of the rights granted by the license (to copy, modify, or redistribute the work) without observing the applicable conditions exceeds the licensee’s authority, and renders that use unauthorized (and, thus, infringing).

Many of the GPL’s conditions exist to inform downstream users about the legal status of the work and to provide them with the resources necessary to execute the rights granted under the license. To ensure that licensees are able to exercise their power to alter the software, the GPLv3 mandates that the software’s source code also be made available whenever the software is distributed in executable or binary form.