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diff --git a/content/learn/participate/derived-works.md b/content/learn/participate/derived-works.md index 8e10229..d135a50 100644 --- a/content/learn/participate/derived-works.md +++ b/content/learn/participate/derived-works.md @@ -2,3 +2,73 @@ title: Re-using free software weight: 90 --- + +One of the great advantages of free software is its potential for re-use. You +can incorporate code from other free software projects into new projects, saving +time and allowing you to build on the shoulders of giants. Of course, you have +to respect the original project's work, and that means complying with their free +software license terms. + +{{< tip "warning" >}} +Always read the license carefully when incorporating someone else's work into +your own software. +{{< /tip >}} + +## Incorporating permissive software into new works + +The main appeal of permissive software licenses is the ability to incorporate it +into anything with relatively little obligation towards the copyright holders. +Most permissive licenses require only that you include the license text, or even +just a copyright statement, in your product. For free software projects which +incorporate permissively licensed code into their work, meeting these +obligations is is usually as straightforward as including an additional license +with your source code. + +When incorporating permissively licensed free software into non-free works, you +must distribute the free software license and/or copyright attribution with your +software. Many commercial users of permissively licensed free software include a +menu somewhere in their product which enumerates the applicable software +licenses, or include a printed version with the product. You will need to come +up with a similar approach. + +## Incorporating copyleft software into new works + +{{< tip "warning" >}} +Copyleft software **cannot** be incorporated into non-free software. +{{< /tip >}} + +Most free software can be incorporated into copyleft software, and vice versa, +if the licenses are **compatible**. As a general rule, most popular permissive +licenses -- but not all -- are compatible with most popular copyleft licenses. +*Some* copyleft licenses are compatible with other copyleft licenses (for +instance, the Mozilla Public License 2.0 is compatible with the GNU family of +licenses), but many are not. Any two projects which use the *same* copyleft +license are compatible with each other and may share code freely. + +{{< tip >}} +GNU maintains a list of licenses which are compatible and incompatible with the +GPL family of copyleft licenses [here][0]. + +[0]: https://www.gnu.org/licenses/license-list.html +{{< /tip >}} + +Incorporating permissive code into a copyleft project is straightforward if the +licenses are compatible: see the previous section. + +{{< tip "warning" >}} +The inverse, incorporating copyleft software into a permissively licensed +software project, is less straightforward. In this case, the combined work +becomes subject to the terms of the copyleft license. Managing a mix of +permissive and copyleft licenses in a single work is possible, but has important +and meaningful implications for your project. This is strongly advised against +for non-experts: don't mix copyleft code into a permissive project unless you +are prepared for the project to [switch to a copyleft +license](/learn/participate/copyright-ownership/#changing-a-projects-license). +{{< /tip >}} + +## Managing many licenses and copyrights in one project + +Larger and more complex projects may incorporate software from many different +sources with many different licenses and copyright holders. If this describes +your project, we recommend that you consider applying the +[REUSE](https://reuse.software/) specification to your work. |