Add "Free software licenses"

1 files changed, 144 insertions, 0 deletions

diff --git a/content/learn/licenses.md b/content/learn/licenses.md
index 6d976d0..ed5dab2 100644
--- a/content/learn/licenses.md
+++ b/content/learn/licenses.md
@@ -2,3 +2,147 @@
 title: Free software licenses
 weight: -9
 ---
+
+The [four freedoms](/learn/four-freedoms/) are generally guaranteed through the
+use of a **free software license**. There are many different kinds of licenses
+with many different trade-offs to suit each software project's unique situation.
+
+## How a free software license works
+
+A free software license grants the necessary rights, perhaps subject to
+some caveats (such as attribution requirements), to establish the four freedoms
+for recipients of the software. Any software license can be a free software
+license if it upholds the four freedoms, but in practice most projects pick from
+one of a few licenses established for general use.
+
+Comments on specific general-purpose software licenses and how to choose between
+them for your own projects are addressed in
+[choosing a license](/learn/participate/choose-a-license/).
+
+Generally speaking you will encounter a free software license in the "LICENSE"
+or "COPYING" file in the software source code. Other projects, particularly
+those which pull together source code from many sources, have more intricate
+ways of explaining their licensing situation. A common approach to managing this
+is the [REUSE specification][0].
+
+[0]: https://reuse.software/
+
+If you want to know more about how free software licenses work in detail, read
+on. Otherwise:
+
+{{< button "/learn/participate" "Next: Getting started" "next-button" >}}
+
+## Common traits of free software licenses
+
+To understand your obligations under any particular license, you will have to
+read it (and perhaps consult a lawyer, especially if you represent a business).
+However, most free software licenses have some traits in common with others, and
+you get get a simple understanding of them by learning about a few essential
+traits. Here are some common features of free software licenses:
+
+### Attribution
+
+Attribution clauses require you to **attribute** the authors when distributing
+or reusing software based on a license with such a clause. This generally
+involves reproducing the license in full, or sometimes a simple copyright
+notice, when you distribute the software, modifications to it, or new software
+which incorporates some or all of the software.
+
+Here's an example from the [MIT license]:
+
+> Permission is hereby granted, free of charge, to any person obtaining a copy of
+> this software and associated documentation files (the “Software”), to deal in
+> the Software without restriction, including without limitation the rights to
+> use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+> the Software, and to permit persons to whom the Software is furnished to do so,
+> subject to the following conditions:
+> 
+> <strong style="color: var(--theme)">The above copyright notice and this permission
+> notice shall be included in all copies or substantial portions of the
+> Software.</strong>
+
+[MIT license]: https://mit-license.org
+
+### Disclaimer of warranty
+
+Free software is often provided as a gift. In exchange for this gift, you often
+are asked to agree to accept the software as-is, without any particular
+expectations of support or warranty from the publisher. This **disclaimer of
+warranty** is used to disclaim liability for free software, so the recipient is
+responsible for what they do with it.
+
+Here's an example from the [MIT license]:
+
+> THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+> IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+> FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+> AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+> LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+> OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+> SOFTWARE.
+
+### Use of trademarks and patents
+
+Software licenses generally deal with copyright-related rights, but commercial
+software publishers often hold other kinds of intellectual property, namely
+trademarks and patents. Free software licenses often incorporate clauses which
+address the relationship between the software's copyright grant and other <abbr
+title="Intellectual Property">IP</abbr>, for example agreeing that use of the
+software does not infringe on the copyright holder's patents, or forbidding the
+use of the copyright holder's trademarks.
+
+Here's an example from the [Apache 2.0 license]:
+
+> 3. **Grant of Patent License.** Subject to the terms and conditions of this
+>    License, each Contributor hereby grants to You a perpetual, worldwide,
+>    non-exclusive, no-charge, royalty-free, irrevocable (except as stated in
+>    this section) patent license to make, have made, use, offer to sell, sell,
+>    import, and otherwise transfer the Work, where such license applies only to
+>    those patent claims licensable by such Contributor that are necessarily
+>    infringed by their Contribution(s) alone or by combination of their
+>    Contribution(s) with the Work to which such Contribution(s) was submitted.
+>    If You institute patent litigation against any entity (including a
+>    cross-claim or counterclaim in a lawsuit) alleging that the Work or a
+>    Contribution incorporated within the Work constitutes direct or
+>    contributory patent infringement, then any patent licenses granted to You
+>    under this License for that Work shall terminate as of the date such
+>    litigation is filed.
+
+[Apache 2.0 license]: https://www.apache.org/licenses/LICENSE-2.0.html
+
+### Copyleft
+
+Some licenses don't just *permit* you to share your improvements, but *require*
+you to share your improvements. Such licenses are **copyleft** licenses, and if
+you make changes to them you are required to share those changes with others
+under the same free-software terms. Copyleft is a tool to protect free software
+from being incorporated into non-free works.
+
+Here's an example from the [Mozilla Public License 2.0]:
+
+> All distribution of Covered Software in Source Code Form, including any
+> Modifications that You create or to which You contribute, must be under the
+> terms of this License. You must inform recipients that the Source Code Form of
+> the Covered Software is governed by the terms of this License, and how they
+> can obtain a copy of this License. You may not attempt to alter or restrict
+> the recipients’ rights in the Source Code Form.
+
+[Mozilla Public License 2.0]: https://www.mozilla.org/en-US/MPL/2.0/
+
+{{< tip >}}
+Copyleft is covered in detail in [What is Copyleft?](/learn/copyleft)
+{{< /tip >}}
+
+### License compatibility & sublicensing
+
+The ability to combine many works together is an essential trait of the free
+software ecosystem, but the use of many different copyright licenses can make
+this work more difficult. This is where **sublicensing** and **license
+compatibility** comes in: many free software licenses make provisions wherein
+they can be extended by the terms of additional licenses. This allows you to
+combine software with two or more compatible licenses to produce new software
+subject to the license terms of both.
+
+Not all licenses have terms which are compatible with one another; in particular
+copyleft licenses tend to be less compatible with others. Software with
+incompatible licenses cannot be combined into one work.