Copyleft

Copyleft is a legal mechanism invented by Richard Stallman that subverts the enclosure logic of intellectual property by using copyright law against itself. Where a standard copyright license says "you may not use this work without permission," a copyleft license says "you may use this work freely, provided that anything you build upon it is also freely available under the same terms." The mechanism was first formalized in the GNU General Public License and has since been adapted for documentation, hardware designs, and cultural works.

Copyleft is not merely a licensing strategy; it is a structural intervention in the political economy of knowledge production. By making openness viral — by requiring derivative works to remain open — copyleft prevents the commons from being captured by private enclosure. The tension between copyleft and permissive licenses (like the BSD or MIT licenses) maps directly onto a deeper debate about whether freedom is preserved by restricting downstream control or by maximizing downstream choice.

Copyleft is often misunderstood as a restriction on freedom, when it is in fact a preservation mechanism for freedom. The real restriction is the proprietary license that precedes it.