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I was interested in the recent conversation about whether WordPress themes need to be licenced under the GPL or whether they can be closed source. The video can be reached from matts blog and my favourite discussion about it is Dave Winers blog post.

My question is - am I allowed to license my theme under the aGPL? or is this the same argument as if I wanted to use a closed source license?

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There's a podcast about this: mixergy.com/chris-pearson-matt-mullenweg -- Chris Pearson and Matt Mullenweg talking about the issue. –  artlung Aug 11 '10 at 19:41

4 Answers 4

up vote 12 down vote accepted

Since WordPress is licensed as GPLv2, you can license any addition (i.e. theme) with a license that's compatible with version 2 of the GPL. Now here's the unfortunate part ... version 1 of the aGPL is not compatible with any version of the GPL. Version 3, however, is compatible with GPLv3 ... but not GPLv2.

Short answer: no, you can't license a WordPress theme with aGPL because neither version of the aGPL is compatible with WordPress' license (GPLv2).

Link to license compatibility chart for reference ...


Strictly speaking, yes. WordPress themes are considered derivative works, so they must be licensed in a fashion compatible with the core project. WP is licensed as GPLv2+, so you can (if you want to) upgrade it to GPLv3 for distribution.

That's important, because the only version of the aGPL that's compatible with the GPL is version 3 ... so your theme must be aGPLv3.

That said, you're under no expectation to redistribute WordPress on your own ... I'm just pointing out the compatibility here. But to keep things simple, I will always advise against using the aGPL. In practice, it doesn't lend well for WordPress themes (feel free to ask me why, but that's beyond the scope of this question).

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super info - thanks a lot. –  Tom Aug 11 '10 at 19:54
I see a way to do anyway, it's sort of a gray area: You can re-distribute wordpress under GPL v3 and then in a friendly manner rely to the comment on compability of the FSF regarding GPLv3 and aGPLv3. Sort of both are compatible so to say then. And hell no, it's not the same as with closed source. –  hakre Aug 17 '10 at 13:53
@hakre Yes, that's a potential workaround ... but it requires you to be willing and able to redistribute WordPress ... –  EAMann Aug 17 '10 at 14:22
.. which should not be a problem. The grey area is not the redistribution of wordpress, that's pretty well defined, the grey area is to say aGPL is compatible to GPL. But I think it's always good to not have a too narrow view, so I think it's valid. –  hakre Aug 18 '10 at 8:00
+1 for the useful link. Thanks –  Jonathan Day Sep 1 '10 at 0:06

Adding a reference to updated @EAMann's answer: I've asked similar question to license@fsf.org.

My exact question was:

Could you please clarify what does it mean to release source code under "GPLv2 (or later)" and if so, if it allows to release derivate works under aGPL v3.

And the answer that came:

By licensing their work under GPLv2 (or later), which I will refer to in this email as GPLv2+, the copyright holders of Wordpress have explicitly permitted you to further distribute their work under any later version of the GPL. By upgrading you can further distribute their work under GPLv3, GPLv3+, GPLv4 (doesn't exist yet, but if it did you could choose it), GPLv4+, etc. This is spelled out in section 9 of GPLv2 and section 14 of GPLv3.

Once you've upgraded the work to GPLv3 (you update the license version number and include a copy of GPLv3, add your own copyright notices as needed, but otherwise keep the original copyright notices and license notices intact), two things will happen: First, the work becomes incompatible with GPLv2-only code; both GPLv2 and GPLv3 are strong copyleft licenses and they cannot both be satisfied at the same time. Second, and more important for you is that under section 13 of GPLv3, and section 13 of AGPLv3, you will now have a narrow compatibility with works licensed under AGPLv3. Which is to say that while you cannot re-license the work, as a whole, from GPLv3 to AGPLv3, you will be able to further distribute the combination of GPLv3 code (the upgraded Wordpress code) and AGPLv3 code (your additional code).

Yoni Rabkin, volunteer at the FSF GPL Compliance Lab

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Yes, you are allowed to license your theme under any license you see fit. Some might not be appropriate for redistribution then. But first of all you are free to choose. It's free software, extend as you wish.

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"Some might not be appropriate for redistribution then" - Which then means that you cannot distribute the theme to anyone, not even a customer, since distributed themes must be released under GPL or a GPL-compatible license. –  Emil Vikström Jan 24 '14 at 13:33

One sentence summary from Matt Mullenweg : PHP in WordPress themes must be GPL, artwork and CSS may be but are not required.

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Please don't always pull Matt Mullenweg out of the pocket. He's no studied lawyer, just has his own opinion. –  kaiser Feb 15 '11 at 15:29
@kaiser: Agreed. Although I've only been hanging around WP for about 6 months, I've noticed a disturbing similarity between how some people refer to "Matt" and how Scientologists refer to "Ron" or "LRH". Matt did some good work and is very powerful within the world of WP, but he's not God. –  Peter Rowell Mar 8 '11 at 3:24
I very much like your thought process and nobody should be seen godlike. That said I think Matt has consulted lawyers on that and that statement is credible. If he was just about abusing the community and it's blind following he would have said all needs to be 100% GPL. It also makes 100% sense since themes need WP core php functions to work. They not necessary need the few css classes it creates. But if you would see it very strict (opinion) you might even say if they use CSS to style .alignright and .wp-caption the CSS is also build upon WordPress core code ^^ –  James Mitch Apr 28 '13 at 23:00

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