Permissive software license facts for kids
A permissive software license is like a special set of rules for computer programs. These rules let people use, change, and share the software with very few limits. Think of it as a "do almost anything you want" pass for code!
Unlike some other licenses that have strict rules about sharing changes (called copyleft), permissive licenses are much more relaxed. They usually just ask you to keep the original copyright notice and don't hold the creators responsible if something goes wrong with the software.
Some well-known examples of these licenses include the MIT License, BSD licenses, and the Apache license. The MIT License is one of the most popular free software licenses used today.
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What is a Permissive License?
The Open Source Initiative (a group that promotes open-source software) says that a permissive license is a "non-copyleft license that guarantees the freedoms to use, modify and redistribute." This means you're free to do almost anything with the code.
GitHub's website, which helps people choose licenses, describes the popular MIT License as one that "lets people do anything they want with your code as long as they provide attribution back to you and don't hold you liable." This means you need to say who originally made the code, and you can't blame them if your project has problems.
Law experts at California Western School of Law explain that "BSD-like" licenses (like BSD, MIT, and Apache) are very flexible. They mostly ask you to give credit to the original creators in your own code or documents.
How Permissive Licenses Compare to Copyleft Licenses
Permissive licenses are quite different from copyleft licenses.
Copyleft Licenses: Sharing Changes
Copyleft licenses usually require that if you change a piece of software, you must share your changes under the same copyleft license. This helps make sure the software stays free and open for everyone to use and improve.
Permissive Licenses: More Freedom
Permissive licenses, on the other hand, don't try to force you to keep your changes open. They generally only ask that you keep the original copyright notice. This means that if someone takes software with a permissive license, they can change it and then sell their new version as a secret, private program.
For some developers, this freedom to use and even sell modified code is a big advantage. For others, it's important that their work always remains free and open for everyone.
Permissive licenses also make it easier to combine different pieces of software. This is because their rules are so flexible that they usually don't conflict with other licenses. Copyleft licenses can sometimes be tricky to mix and match because their sharing rules might clash.
Permissive Licenses vs. Public Domain
Sometimes people confuse permissive licenses with software that is in the public domain. However, they are not quite the same.
Public Domain: No Rules
When something is in the public domain, it means there are no copyright restrictions at all. Anyone can use it for any purpose without asking permission or giving credit. It's like it belongs to everyone.
Permissive Licenses: Small Rules
Permissive licenses usually have a few small requirements. For example, they often require you to give credit to the original authors (this is called attribution). While giving credit is often a good idea even for public domain works, it's usually a legal requirement for permissively licensed software.
Some experts even suggest using a permissive license instead of trying to put software directly into the public domain. This is because the rules about public domain can be different and complicated in various countries. So, a permissive license acts as a clear way to say, "You can use this freely, but here are a couple of small things to remember."
How Licenses Work Together
Generally, permissive licenses are very good at working with almost all other software licenses. This is called license compatibility.
Because they are not very strict, most permissive software licenses can even be used with copyleft licenses. This is a big deal because copyleft licenses are often hard to combine with other types of licenses.
Some older permissive licenses used to have rules that made them incompatible with copyleft licenses. For example, they might have required you to mention the copyright holder in advertising. But newer, popular permissive licenses like the MIT License and the 3-clause BSD license don't have these kinds of advertising rules, so they usually work well with copyleft licenses.
Other Names for Permissive Licenses
Non-Copyleft
Sometimes, people prefer to use the term "non-copyleft" instead of "permissive." This is because all free software licenses allow you to change and share the code, so in a way, they are all "permissive." But the real difference is whether they have the strict "copyleft" rule or not.
Copycenter
Copycenter is a fun term that was used to describe the BSD licenses. It's a play on the words "copyright" and "copyleft." A computer scientist named Marshall Kirk McKusick explained it by saying, "Berkeley had what we called 'copycenter,' which is 'take it down to the copy center and make as many copies as you want.'" It means you can make copies freely.
Pushover License
Richard Stallman, who started the GNU operating system, sometimes calls permissive licenses "pushover licenses." He compares them to people who "can't say no" because they allow others to take the software and make it private.
However, the Free Software Foundation (which Stallman founded) suggests that these "pushover licenses" can be good for very small programs (under 300 lines of code). For these tiny programs, the benefits of copyleft might not be worth the effort of making sure the license always goes with the software.
See also
In Spanish: Licencia permisiva para niños
- License-free software
- Public domain equivalent license
- Free-software license
- Comparison of free and open-source software licenses
- Free Software Foundation
