What is Copyleft

Copyleft is an approach to managing intellectual property rights, particularly in the realm of software development. As we have seen, it is a distinct departure from the traditional copyright model, promoting freedom and openness instead of restriction and exclusivity.

At its most fundamental level, copyleft uses the framework of copyright law to guarantee that every person who receives a copy or derived version of a work can use, modify, and distribute both the work, and derived versions of the work. To accomplish this, copyleft attaches a condition to the work: that any derivative works be licensed under the same copyleft license. This ensures that future recipients of the software or work also have access to these freedoms.

However, it's essential to note that copyleft licenses do not reject copyright. On the contrary, they depend on copyright law to enforce their conditions. In fact, without copyright law, the terms of copyleft licenses couldn't be applied. This is why copyleft is often described as "hacking" the copyright system: it uses the legal mechanisms of copyright in a way that they were not originally intended to promote the free use, modification, and distribution of works.

Common Misconception of Copyleft

One common misconception about copyleft (and open source in general) is that it is against commercial use. This is not the case. Copyleft licenses allow commercial use and distribution just like any other license. However, they require that the source code remains available and that improvements are shared under the same terms.

Principles of Copyleft

While copyleft licenses can vary in their specifics, they generally share a set of core principles. These principles are rooted in the ethos of the free software movement, which advocates for the freedom to use, study, modify, and distribute software.

• Freedom to Use
  Copyleft licenses grant everyone the unconditional right to use the software for any purpose. This means that there are no restrictions on how, where, or why the software may be used. This freedom enables users to explore the full potential of the software without fear of legal repercussions.

• Freedom to Study
  A key aspect of copyleft is the commitment to transparency. Users have the right to access and study the source code. By allowing users to understand how the software works, this freedom supports education and enables users to make informed decisions about using and modifying the software.

• Freedom to Modify
  Copyleft licenses allow users to modify the software to suit their needs. This could include fixing bugs, adding new features, or altering the software in any other way. The freedom to modify is a significant driver of innovation, as it allows continuous improvement and adaptation of the software.

• Freedom to Distribute
  Lastly, copyleft licenses grant the freedom to distribute original or modified versions of the software. This could involve sharing the software with others, contributing modifications back to the community, or even selling copies of the software. The condition here is that any distribution of the software (whether in its original or modified form) must also be under the same copyleft license, ensuring that these freedoms are passed on to all recipients.

Types of Copyleft

While all copyleft licenses share the core principles of use, study, modification, and distribution, they can be categorized into two main types based on how strictly these principles are applied: strong copyleft and weak copyleft. This distinction is crucial in determining how the software can be used, particularly in the context of combining it with other software.

Strong Copyleft

Strong copyleft licenses are characterized by their strict enforcement of the copyleft principles. Under a strong copyleft license, any derivative work or modified version of the software must also be licensed under the same strong copyleft terms. This means that if you use a piece of software released under a strong copyleft license, and you modify it or incorporate it into your software, your entire software must also be released under the same strong copyleft license.

The most common example of a strong copyleft license is the GNU General Public License (GPL). The GPL ensures that all derivative works are also licensed under the GPL, thereby preserving the four freedoms for all subsequent users and developers. The GPL has been instrumental in the development of many significant open-source projects, including the Linux kernel.

Weak Copyleft

Weak copyleft licenses, on the other hand, are less restrictive. They allow more flexibility in combining the copyleft software with other software, including proprietary software. Under a weak copyleft license, portions of the original software can be used in new software without the new software having to adopt the same license. However, any modifications to the original copyleft software itself must still be released under the same weak copyleft license.

The Lesser General Public License (LGPL) is a well-known example of a weak copyleft license. The LGPL was created to allow developers to use certain libraries in their software without requiring the entire software to be released under the LGPL. This flexibility makes weak copyleft licenses more appealing to certain developers, particularly those developing proprietary software.

References

https://copyleft.org/
https://www.gnu.org/licenses/copyleft.en.html