Compatible Licenses

Posted on February 29, 2008

Open Source software is distributed under a variety of licenses each of which usually permits licensee to distribute and modify the software, provided that the licensee complies with a specified set of terms and conditions.

A question that can therefore arise, is a licensee legally permitted to create modifications which combine elements of two (or more) different existing works into a single work, and distribute the result?

The answer is that these types of combinations are generally only legally permitted if the licensee can comply with all the pertinent terms and conditions of all the licenses.

- In some cases, one license agreement may contain terms and conditions which can not simultaneously be satisfied with the terms and conditions of another, thus making compliance with all the terms and conditions impossible. Such licenses are therefore said to be “incompatible”. It is therefore not legally permissible to combine and distribute code which is under incompatible licenses - because you, as a licensee, will always be in breach of at least one, and possibly more, of the licenses.

- In other cases, it may be possible to simultaneously comply with each license agreement’s terms and conditions. Such licenses are therefore said to be “compatible”. It is therefore is legally permissible (assuming there are no other legal reasons to stop you) to combine and distribute code which is under compatible licenses - provided you, as a licensee, comply with all the pertinent obligations in all of the licenses.

Additionally, it is worth noting that compatibility may only be in one direction. For example:

- It is permissible to use software code which is under some variants of the BSD license in a GPL licensed project, and then to distribute the result under GPL.

- It is not permissible to use software code which is under the GPL license in a BSD licensed project, and then to distribute the result under the BSD license.

Finally, if you are the copyright holder of some code, it is should be possible for you to place your own code under whichever license you want (even if you have licensed it under a different license before - provided that was done a non-exclusive basis) - thus allowing you a lot more flexibility as to which other code you can combine with. Of course, you can not relicense other people’s code in this way - but if you are completely stuck, you do have the option of approaching the author and asking them whether they might consider dual licensing their code.

Please note: The author of this article is NOT a lawyer. This article is NOT intended as, NOR should be construed as legal or professional advice.

Orginally published at http://www.softwarelicenses.org/p1_open_source_glossary_compatible_licenses.php

For more articles and information about software licenses, please visit http://www.softwarelicenses.org/

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