Copyleft is a particular legal tool whose name is a play on the term copyright; where the term “right” recalls the concept of legal right and right side, the term “left” recalls the concept of permission and left side: its effect is in fact a true reversal of copyright.
In practice, its application guarantees the persistence of the rights structure given by the author towards licensees and/or sub-licensees of the n-th generation. This means that every licensee who redistributes the programme to third parties must do so without arrogating the right to operate any kind of restriction: all those who receive the licence will have the same rights granted by the original author, regardless of intermediate steps.
In this sense it is often said that open licences with copyleft are “viral”, to the point that the structure desired by the author will apply not only when distributing copies of the original (the so-called verbatim copy), but also in the case of works that are the result of re-elaboration. Thus, the rights management guaranteed by the licence of the original product must also be applied to the derivative product.
In particular cases, however, specifically identified by the licence, modifications made to the code may be released under another structure, thereby interrupting propagation: this depends strongly on the type of copyleft chosen.
A licence with strong copyleft requires that derivative works also be released under the same licence (for example: the GPL); other licences with weak copyleft (for example LGPL and MPL) require the application of the original licence only in certain cases, so that in the others the “virus” does not transmit. Beyond practical effects, it is also necessary, however, to address copyleft from a strictly legal point of view. Doing so, we can affirm that it represents an obligation to do, on the basis of which the licensee’s compliance can be measured.
The author subordinates the effectiveness of the licence contract to the fulfilment of the obligation to propagate under the same conditions.
Indeed, the most legally elaborated licences — such as the GPL (art. 8, termination), the LGPL (art. 8), and the MPL (art. 8, termination) — contain veritable express resolutive clauses, attributable to the general case provided for by art. 1456 of the Italian Civil Code. Therefore, where the licensee in redistributing the programme — or a derivative of it — does not fulfil the obligation, contract termination occurs (for a case of breach linked to the GPL licence in Europe, see Netfilter vs. Sitecom in German case law of the District Court of Munich).
For this clause to produce its effects in the Italian legal system, the party with an interest in invoking it must communicate that intention to the other (art. 1456, paragraph 2, of the Civil Code).
This last provision is undoubtedly achievable in practice if the relationship takes place in a commercial context, where the licensee’s identifiability by the licensor is presupposed.
In cases of release of the software to the community, however, monitoring the use of the licence and the possibility of communicating the intention to invoke the resolutive clause in case of violation is hardly feasible, given the tendential unidentifiability of the licensees who came into possession of the source code (in order to obtain effectively achievable protection, the Free Software Foundation was established, which, with the permission of the copyright holder, acts to obtain protection of the author’s rights even in the most complicated cases, for example similar to the one described).
In summary, copyleft produces effects between the parties thanks to the licence contract under the rule of art. 1372, paragraph 1, of the Civil Code.
And with regard to third-party sub-licensees? How can the author protect themselves against them, given that there are no contractual relations between them?
The licence, being a contract, is effective only towards the parties, while it does not produce effects on third parties (Art. 1372, paragraph 2, of the Civil Code).
In this case, therefore, contractual protection will no longer be applicable, but it will be necessary to resort to the protection tools of copyright.
A third party who behaves in conflict with the copyleft clause therefore commits, not a contractual offence, but a violation of copyright law. Against them, therefore, the author may not request termination of the contract but will instead seek the application of articles 158 et seq. of the copyright law (Italian Law 633/1941 as subsequently amended). In conclusion, it is noted how the copyleft tool is particularly flexible and functional and allows the aggregation in itself of contractual protection and the protection provided by articles 158 et seq., so that they may support and integrate each other in relation to the conduct held by the licence recipients.