Definition : Copyleft


Copyleft is a contractual technique, born in free software, by which the author authorises the copying, modification and redistribution of his or her work on condition that any derivative version is distributed under the same licence, with the same freedoms and the same access to the source code. It rests entirely on copyright: the author uses his or her exclusive right to require the perpetuation of the freedoms granted. Under French law, it falls within the framework of Articles L. 122-6 et seq. of the French Intellectual Property Code for software and of Article L. 122-7-1 IPC for making works available free of charge.

The mechanism and its degrees

Strong copyleft, embodied by the GNU General Public License, extends the reciprocity obligation to any derivative or combined work distributed to third parties. Weak copyleft, illustrated by the GNU Lesser General Public License or the Mozilla Public License, limits the obligation to modifications of the free component itself and allows its integration into a proprietary whole. At the other end, permissive licences, such as the MIT, BSD or Apache licences, allow reuse without requiring reciprocity. For non-software works, the share-alike clause of Creative Commons licences performs a similar function.

The regime under French law

A copyleft licence is a non-exclusive, royalty-free software licence, whose terms determine the rights granted and their conditions. It leaves intact moral rights, which remain inalienable, and its validity in the light of the formal requirements for assignments is generally accepted provided that the rights, their scope and their duration are specified. Whether a work incorporating a copyleft component is a derivative work, subject to the reciprocity obligation, depends on the mode of integration, dynamic linking and interfaces being the subject of unresolved technical and legal debate.

Litigation

Whether a breach of the conditions of a free licence sounds in contract or in infringement was long debated. The Court of Justice of the European Union holds that the exploitation of software beyond the terms of the licence constitutes an infringement of an intellectual property right falling within Directive 2004/48/EC, whatever the liability regime applicable under national law, and French case law has come round to admitting the action for software infringement in that case. The remedies are then those of infringement, namely an injunction, damages and the recall of products. In practice, the main risk lies in the uncontrolled integration of copyleft components into proprietary software, which may compel the publication of the source code or the rewriting of the component.

Key points

Copyleft makes the freedom to use a work conditional on the redistribution of derivative versions under the same licence, with varying intensity depending on whether the licence is strong or weak. Breaching it exposes the user to an infringement action. Before integrating any free component into a product, take an inventory of the licences involved, characterise the mode of linking and decide between compliance, substitution or rewriting.

This glossary entry is general in scope and does not constitute legal advice.

Dhenne Avocats is a patent litigation firm. Matters outside that field, such as trade marks, designs, copyright and IT contracts, are handled by practitioners the firm works with regularly, and by the firm itself when they arise in a patent dispute.

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