What is the difference between free software and open-source?

Free software and open-source software both involve sharing source code, but they emphasize different values and goals. Free software, defined by the Free Software Foundation (FSF), prioritizes user freedoms. The term “free” refers to liberty, not price, and centers on four essential freedoms: to run the software for any purpose, study and modify its code, redistribute copies, and distribute modified versions. Licenses like the GNU General Public License (GPL) enforce these freedoms through copyleft, ensuring derivative works also remain free. For example, the Linux kernel uses the GPL, requiring any modifications to stay open. Open-source software, defined by the Open Source Initiative (OSI), focuses on collaborative development and practical benefits like reliability and innovation. Permissive licenses like MIT or Apache allow code reuse in proprietary projects, as seen in Microsoft’s VS Code, which builds on the open-source Electron framework.

The philosophical divide is key. Free software advocates view non-free software as unethical, framing access and modification as moral imperatives. The FSF’s GPL ensures these freedoms are preserved across derivatives, prioritizing user rights over developer convenience. In contrast, open-source proponents emphasize technical and business advantages, such as faster innovation or cost reduction. For example, companies like Google adopt open-source (e.g., Android’s AOSP) to leverage community contributions without imposing strict licensing. While the GPL’s copyleft ensures freedom, permissive licenses like Apache 2.0 prioritize flexibility, allowing proprietary forks like Amazon’s Elasticsearch. This distinction reflects differing priorities: ethics versus pragmatism.

Practically, most free software qualifies as open-source (meeting OSI criteria), but not all open-source software is free. For instance, the FSF considers Apache 2.0 compliant with free software principles, but some OSI-approved licenses, like the JSON License, impose restrictions incompatible with freedom (e.g., prohibiting use for evil). Developers choose between models based on goals: those prioritizing user rights opt for GPL, while others prefer permissive licenses for broader adoption. Projects like GCC (GPL) enforce freedom, while tools like React (MIT) thrive in commercial ecosystems. Understanding these differences helps developers align their work with ethical or practical goals, even as the technical overlap remains significant.