> One can't conditionally license some code under GPL.

You can release code under however many incompatible licenses as you'd like, as long as you own all of the code in question.

I think they were referring to the "GPL for non-profit" part of the comment. You either don' release it as GPL at all or you release it as GPL for everyone, which means that for-profit companies can use the software free of charge (as long as they obey the terms of the license).

Yeah, you are correct that you can't add a non-commercial clause to the GPL and have it remain the GPL (or compatible with the GPL in either direction).

You could choose to only grant GPL licenses directly to non-profits. They would be free to pass along the same rights to commercial entities, if they chose. It's possible that in a practical sense this would present enough of a hurdle for larger companies to prefer to pay (but plenty possible that it would not).

It is also possible to grant other licenses for situations where the GPL prevents some particular for-profit activity - that kind of approach is presently making some people some money, although the incentives can be weird.

If you own the software, you can grant specific people and institutions a GPL license for your software, and grant other people and institutions a commercial license (and refuse to grant them a GPL license for your software).

However, everyone who has received your software under the GPL can sublicense it to the people who you denied the GPL to. You can't forbid it, but they don't have to, and you can nicely ask them to never sublicense it.

You're kind of correct in a pedantic nitpicky way. If you release code under the GPL you can't prevent anyone, such as an Enterprise, from using it under that license. But what you can do is also offer it under a commercial license, that commercial customers might be more comfortable with, and let the user choose which license they want to use it under. This is very common and it certainly seemed clear to me that this is what the poster meant.

Well, that enterprise has to receive the software under the GPL license first, and you can absolutely refuse to grant them that, in which case they have to find someone else who has received it under the GPL, and ask that party to sublicense it to the enterprise under the GPL.

Two libraries used by Octave, FFTW and SuiteSparse, both do exactly this - GPL for open source usage, or commercial paid licenses for inclusion in proprietary software (like Matlab).

Selling software via a proprietary license to an enterprise can be bad for open source because it means that the enterprise doesn't need to obey the terms of the GPL. They are free to modify and adapt the code without contributing the changes back to the community, which kind of ruuing the point of the GPL in the first place.

This method also only works if the copyright if fully owned by a single person or entity, with all code contributors signing a contributor licensing agreement to give away their copyrights to a single entity. This is problematic because now there is the possibility that this single entity gets bought out by an evil corporation (say, Oracle), which can choose to continue developing the project without releasing the modifications under an open source license.

>They are free to modify and adapt the code without contributing the changes back to the community, which kind of ruuing the point of the GPL in the first place.

As they are with the GPL so long as they don't distribute the modified code outside of the organization.

If they receive a copy of the software under a non-GPL license they might also be allowed to redistribute modified versions without releasing the source code. (This is usually the whole point of having the proprietary dual-licensing scheme).

Selling commercial license also gives you cold hard cash, with which you can buy ramen so that you can continue developing said software.

Contributing to the community is all good, but you know, eating is slightly higher on the priority list.