What are the pros and cons of copyleft vs permissive licenses?

For copyleft licenses, the source code must be made available when distributing binaries. There are certain conditions on how the code can be used. These licenses are often selected when you don’t want your code made proprietary by someone else. A weak copyleft license imposes fewer restrictions, such as the MPL 2.0, EPL, and CDDL. A strong copyleft license enforces stricter conditions, requiring that the license also apply to derivative works or any project using the licensed code, as seen with the GNU GPL 3.0 and AGPL. It's estimated that just over 20% of open source software projects use a copyleft license (with the rest using a permissive license).

Les licences copyleft obligent à partager les modifications du logiciel sous la même licence libre. Cela garantit que le code source reste ouvert et modifiable par tous. Exemples: GPL, LGPL, MPL.

Permissive Licenses: Pros: Permissive licenses, such as MIT or Apache, offer flexibility, allowing extensive use and modification without imposing stringent conditions. This fosters wide adoption, encourages collaboration, and facilitates integration into commercial projects. Cons: While these licenses promote broad usage, they may not provide strong protection against proprietary exploitation. Developers may contribute to your project without being obligated to share modifications, potentially impacting your control over the project's evolution. Balancing openness with project sustainability is crucial when considering permissive licenses.

While copyleft licenses come in neatly boxed categories such as “strong” and “weak”, permissive licenses tend to have their own peculiarities. Examples: The MIT License is known for its conciseness, ease of use, and flexibility. BSL is similar but does not require the inclusion of a copyright notice or license text unlike the MIT License. BSD 3 is another license of the same family but prohibits the use of the project name or contributor to market the derivate work without explicit permission

Les licences permissives autorisent l'utilisation, la modification et la distribution du logiciel open source sans obligation de partager le code source modifié. Cela permet l'intégration dans des produits propriétaires. Exemples: MIT, Apache, BSD.

Copyleft licenses, like GPL, enforce reciprocity, ensuring that modifications and derivative works are also open source. This maintains a strong commitment to open collaboration and prevents proprietary appropriation of the codebase.

Les licences copyleft garantissent que le logiciel reste libre et ouvert, permettant à tous de bénéficier des améliorations. Elles favorisent la collaboration, la transparence et protègent contre l'exploitation commerciale en interdisant les restrictions supplémentaires.

The strong reciprocity requirement can be a deterrent for commercial entities looking to integrate or distribute the software in proprietary products. It may limit broader adoption but ensures that modifications to the codebase remain open, preserving the project's open nature. Balancing between openness and commercial viability is a consideration with copyleft licenses.

Copyleft licenses require that modified open source software must also release the source code of that program. Not ideal for large software enterprises looking to keep their IP under wraps

Les licences copyleft imposent des obligations strictes qui peuvent limiter la flexibilité des développeurs. Elles créent des problèmes de compatibilité entre licences et découragent certaines entreprises de contribuer pour protéger leur code propriétaire.

Pros of Permissive Licenses: 1. Flexibility: Offers maximum freedom for code use. 2. Commercial Adoption: Attracts businesses due to fewer restrictions. 3. Community Collaboration: Encourages diverse contributions. 4. Integration: Facilitates open-source integration into proprietary projects. 5. Reduced Legal Complexity: Simplicity in terms reduces legal complexities. 6. Accelerated Development: Lowers barriers, fostering a collaborative environment.

One thing I've found helpful is to understand the difference between a piece of code that you are going to use or attribute to your work and a working collection of code such as a permissively licensed software library. The permissive license gives you the right to extend, refactor, or just use a portion of the licensed software. This is a pro for the use of permissively licensed software but, I don't see the con where the software may not always be there or taken down from public availability because it wasn't written just for you initially. I discount any cons of permissive licensed software.

Permissive licenses offer great flexibility in that there is little restriction how others use your source code and reshare the software. They also include a high level of combability allowing to combine different pieces of software and distribute them together

Les licences permissives offrent liberté et flexibilité aux développeurs en permettant l'utilisation, la modification et la distribution sans restriction. Elles encouragent l'innovation, l'adoption et la compatibilité avec d'autres licences et produits.

Permissive licenses should be mentioned first, since they are much more popular and practical. Also, note that in practice, copyleft licenses are often subverted as part of a dual-licensing scheme whereby the free and open-source version is effectively crippled with a copyleft license, and then the owner sells expensive proprietary licenses for those who need more flexibility. It must be emphasized that many companies and developers will in general do their best to stay far away from copylefted code, if only to avoid gratuitously imposing impractical restrictions on their (potential) downstream users. Adopting a copyleft license should never be taken lightly, despite a few big success stories such as the Linux kernel.

The appropriate Open Source License will very much depend on the use case and circumstances. 1. What is the intention of adopting Open Source; to use but not modify it, or alter and redistribute? A large enterprise company with a lot of Intellectual Property within its apps may prefer licenses that enable them to keep their code under wraps. 2. Are you looking to contribute to or just leverage Open Source? e.g. a permissive license allows users to change code, adopt it in their proprietary software without releasing the code. If the code is destined for commercial distribution, then this will narrow down the number of appropriate licenses.