Copyleft

Excerpt
Copyleft is a general method for making a program (or other work) freely available to the public while ensuring that all derivatives of the work are also open and free. It is a play on the word "copyright," with a twist: instead of restricting the use of a work, copyleft aims to promote freedom and sharing by ensuring that any modified versions of a work must also be distributed under the same open terms. Copyleft is a fundamental principle in free and open-source software licensing, particularly in the GNU General Public License (GPL).

Summary
Copyleft is a licensing technique used primarily in free software to ensure that the freedoms granted to users to run, modify, and share software are preserved in derivative works. Unlike traditional copyright, which allows creators to restrict the use and distribution of their work, copyleft requires that any modified versions of the work be licensed under the same terms as the original. This concept promotes the idea that the freedom to use, share, and improve software should be preserved for all users, ensuring that software remains free and open for future generations.

Deep Dive

Key Features of Copyleft

1. Freedom to Use
   Copyleft ensures that users have the right to use the software for any purpose, without any restrictions on how it can be used.
2. Freedom to Modify
   Users can modify the software, whether to improve it, adapt it to their needs, or learn from the source code. This is a cornerstone of the copyleft philosophy, promoting customization and innovation.
3. Freedom to Share
   Copyleft guarantees the right to distribute copies of the original software or its modified versions. This freedom ensures that software can be shared with others, contributing to the open-source ecosystem.
4. Derivative Works Must Be Copylefted
   The most crucial aspect of copyleft is that any derivative works (i.e., modifications or adaptations of the software) must be distributed under the same copyleft terms as the original. This prevents proprietary forks and ensures that future versions of the software remain open and free.

Copyleft vs. Copyright

• Copyright: Traditionally, copyright grants the creator of a work exclusive rights to its use and distribution, including the right to prevent others from modifying or distributing the work. Copyright is intended to protect the creator's economic interests, allowing them to control how their work is used.
• Copyleft: In contrast, copyleft uses the framework of copyright law but flips its intent. Instead of granting exclusive rights, it ensures that the freedoms to use, modify, and share the work are preserved. Copyleft licenses explicitly require that any modifications or redistributed versions of the software carry the same freedoms.

Copyleft Licenses

The most famous copyleft license is the GNU General Public License (GPL), created by Richard Stallman for the Free Software Foundation. Under the GPL, any software released must allow users to freely copy, modify, and distribute the software, but if the software is modified and redistributed, it must be under the same GPL license.

Other copyleft licenses include:

• GNU Lesser General Public License (LGPL): A more permissive version of the GPL, allowing proprietary software to link to LGPL-licensed libraries under certain conditions.
• Affero General Public License (AGPL): Similar to the GPL but with a clause that requires modifications to be made available to users who interact with the software over a network (e.g., web applications).
• Mozilla Public License (MPL): A more flexible copyleft license that allows proprietary software to use portions of MPL-licensed code while ensuring that any changes to the MPL-licensed code itself are released under the same license.

Advantages of Copyleft

• Preservation of Freedom: Copyleft ensures that software remains free and open, fostering a culture of sharing and collaboration. It prevents software from becoming closed-source after being modified.
• Encouraging Innovation: By ensuring that modifications to software remain open and free, copyleft encourages the community to innovate, improve, and build upon existing software.
• Community Empowerment: Copyleft licenses empower users by ensuring that they have control over the software, allowing them to contribute to its development and share improvements with others.

Challenges of Copyleft

• Restrictiveness: Some developers or businesses find copyleft licenses too restrictive, especially if they want to incorporate open-source software into proprietary products. Copyleft requires that modifications to the original work be open-sourced, which can be a barrier for companies that wish to keep their adaptations proprietary.
• Legal Complexity: Copyleft licenses, particularly the GPL, can be legally complex, requiring organizations to carefully ensure that they comply with the terms when using or redistributing copylefted software. Violations can result in legal action, which may deter some users from adopting copyleft-licensed software.
• Compatibility Issues: Copylefted software may be incompatible with other licenses. This can cause challenges when combining software from different projects, particularly if one uses a strong copyleft license like the GPL and another uses a permissive license like the MIT License.

Copyleft in the Software Industry

Copyleft has played a significant role in the development of free and open-source software (FOSS). It has been a cornerstone of many high-profile open-source projects, including the Linux kernel, the GNU operating system, and many others. The GPL has ensured that software like the Apache HTTP Server, LibreOffice, and MySQL remains free and open, benefiting both individuals and organizations.

While copyleft licenses may not be as commonly used in proprietary software, they have been vital for many large-scale projects, particularly those that operate within the open-source ecosystem. The copyleft model allows for a thriving community-driven development model, where developers can freely contribute to projects without fear of having their work closed off by commercial interests.

The Ethical and Philosophical Basis of Copyleft

Copyleft is rooted in the ideals of free software, which emphasize the ethical aspects of software development. Richard Stallman, the founder of the Free Software Foundation, argued that software should be a tool for empowerment, not exploitation. Copyleft is designed to ensure that users retain control over software, preventing it from becoming proprietary or locked away by companies looking to profit from its use.

Stallman’s vision of software freedom is based on the idea that users should have the freedom to:

• Run the software for any purpose.
• Study the software and adapt it to their needs.
• Distribute copies of the software to help others.
• Improve the software and share those improvements with the community.

Copyleft and Other Creative Works

Although copyleft is most commonly associated with software, the principles have been extended to other forms of creative works, such as art, literature, and music. The Creative Commons licenses, for example, allow creators to apply open terms to their works while retaining control over certain aspects, like attribution. Some Creative Commons licenses incorporate copyleft principles, ensuring that derivative works are also made available under the same terms.

Related Concepts

• Free Software: Software that is free to use, modify, and distribute, often associated with the copyleft movement but not always linked to it. Copyleft specifically ensures that derivatives remain open.
• Open Source: While open source shares many principles with copyleft, open-source licenses may be less restrictive about derivative works becoming proprietary. Copyleft ensures that software remains free in perpetuity.
• Permissive Licenses: Licenses such as the MIT License and the Apache License allow for greater flexibility in how software can be modified and distributed, including the possibility of incorporating the software into proprietary applications.
• Public Domain: Works in the public domain are no longer under copyright protection and can be freely used, modified, and distributed, without requiring any form of copyleft.

Conclusion
Copyleft represents a unique approach to software licensing, emphasizing freedom, collaboration, and the preservation of open access to software. It ensures that any improvements to a work remain accessible to everyone, preventing proprietary forks from locking away software and knowledge. While it can be seen as restrictive to businesses and developers who want to use software in closed-source projects, it has played a pivotal role in fostering innovation and creating a robust, community-driven software ecosystem.