Permissive software license facts for kids
A permissive software license is a special kind of software license that lets people use, change, and share computer programs with very few rules. Think of it like sharing your toys: you let your friends play with them, change them a bit, and even share them with others, as long as they don't claim they made the toy themselves or blame you if it breaks. These licenses are sometimes called "BSD-style" because some of the first ones came from the BSD operating system.
Unlike some other licenses that make sure the software always stays "free" (called copyleft licenses), permissive licenses allow others to take the code and use it in their own secret, paid programs. This means the software might not always stay open for everyone to see and change.
Some well-known permissive licenses include the MIT License, BSD licenses, and Apache license. The MIT License is one of the most popular free software licenses used today.
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What are Permissive Licenses?
Permissive licenses are designed to give developers and users a lot of freedom. They usually only ask for a few things:
- Attribution: You must mention the original creators of the software. It's like saying "Thanks to the person who made this!"
- Warranty Disclaimer: The original creators usually say they aren't responsible if something goes wrong with the software. This protects them from legal problems.
These licenses are very flexible. They let people use the code in many different ways, even in projects that are not open source.
How Permissive Licenses Compare to Other Licenses
Software licenses can be grouped by how much freedom they give.
Permissive vs. Copyleft Licenses
Copyleft licenses are different from permissive licenses. Copyleft licenses usually say that if you change a program and share it, your new version must also be shared under the same copyleft license. This helps make sure the software always stays free and open for everyone.
Permissive licenses don't have this rule. You can take software with a permissive license, change it, and then sell your new version without sharing its code. This can be good for businesses that want to use open-source code in their own products. However, it also means that a program that was once open and free could become a closed, paid program.
For example, imagine you have a recipe.
- A permissive license is like saying, "Here's my recipe. You can change it, sell the food you make, and you don't have to share your changes to the recipe."
- A copyleft license is like saying, "Here's my recipe. You can change it and sell the food, but if you share your changed recipe, you have to share it with everyone for free, just like I did."
Permissive vs. Public Domain
When something is in the public domain, it means there are no copyright rules at all. Anyone can do anything they want with it, without asking permission or giving credit.
Permissive licenses are not exactly the same as public domain. While they give a lot of freedom, they often still require you to give credit to the original authors. This is a small but important difference. In some places, it can be tricky to put software truly into the public domain, so permissive licenses are a clear way to share code with lots of freedom while still protecting the original creators a little bit.
Why License Compatibility Matters
When you combine different pieces of software that have different licenses, you need to make sure their rules don't clash. This is called license compatibility.
Permissive licenses are usually very compatible with most other software licenses. Because they have so few rules, it's often easy to mix code with a permissive license with code that has a different license, even copyleft licenses.
However, some older permissive licenses had a rule that said you had to mention the copyright holder in advertising materials. This made them incompatible with some copyleft licenses. Luckily, most modern permissive licenses, like the MIT License and the 3-clause BSD license, don't have this advertising rule, so they work well with many other licenses.
Other Ways to Describe Permissive Licenses
Sometimes, people use other words to talk about permissive licenses.
Non-copyleft
Since the main difference between permissive licenses and other free software licenses is that they don't have copyleft rules, some people simply call them "non-copyleft" licenses. This term clearly shows that they don't force you to share your changes.
Copycenter
This is a playful term that was used to describe the BSD licenses. It's a word play on "copyright" and "copyleft." It means you can "take it down to the copy center and make as many copies as you want." It highlights how easy it is to copy and share software under these licenses.
See also
- License-free software
- Public domain equivalent license
- Free-software license
- Comparison of free and open-source software licenses
- Free Software Foundation
