I released my project under GPL. Can I still use it in my commercial app?

Question

So I have this super sweet library I'm working on. Let's say I release it into the wild under GPL. In tandem I'm working on a commercial piece of software, and I'd like to use this library in it.

Since I made the library in the first place (even though I made it GPL), is it safe to assume I can use it in the commerical app?

Now that it's released as GPL, lets say some people make some awesome updates to it. Their work is also under GPL. Therefore I cannot include their changes in my commercial app, unless I wanted to make my commerical app GPL as well (which I don't). In that scenario, the safest thing to do would be to use my library as it was originally released when it was 100% my own code.

Is the above correct? If so, would releasing my library under LGPL be a better idea so I can re-incorporate changes to it into my commercial app since I'll just be linking to the DLL?

Edit after Thomas' answer:

To add a bit about the dual licensing option, it does open up the world of being able to commercially sell my library. On the other hand, I really want to bring in other developers to improve it (if they want), which kind mucks up the commercial licensing aspect. What is more important? For me, I'd rather have a better library than make a couple bucks off of it (it's not THAT impressive), so Thomas' point about going with LGPL is perfect. That allows me to both solicit assistance, and to take advantage of other contributors I can simply link to the DLL inside of having the original code baked into my solution file. The important bit is that I can use this improved code in my main commercial app and I won't worry about commercializing a subset of it (this library).

Answer 1

Yes, you can release the portions that you own (in this case, the library before modifications were made by other contributors) under one or more other licenses. Those other licenses could be anything that you want, from other open source licenses to specific licenses to other people or organizations.

If you are producing a library that is meant to be linked to, then releasing it under the LGPL would probably be better. It would ensure that modifications to your library remain open and free, while letting people link to the library in closed-source applications.

It's easiest to make licensing decisions before you release the software to the public, and definitely before other people have contributed. Once other people contribute, you can't simply change the license on someone else's work.

Answer 2

Yes, as @ThomasOwens said, you can use the portions that you own (that you wrote) in a closed-source, non-gpl app.

I think what clarifies this, but hasn't been mentioned, is the distinction between license and copyright. You, the author of the code, own its copyright despite licensing the code under gpl. In fact, you should immediately, if not sooner, go to http://www.copyright.gov and set up an account. Then register your copyright (Form TX) online. This is especially important when you intend to use that code commercially. If copyright matters ever come under dispute, courts look very favorably on you if you've registered the copyright before infringement occurs.

As for gpl, that's just a license issued by the copyright holder. And the gpl specifically prohibits using licensed code in closed-source projects. But you're not a licensee. You're the copyright owner. So you can do what you want. But, exactly like you said, you won't own the copyright to contributions to your codebase from other programmers. You'll be a licensee to their copyrighted code, and they'll be a licensee to your copyrighted code.

Again, go to http://www.copyright.gov and register the copyright to your code. Even if you don't intend to use it commercially, it just costs a few bucks, and it concretely establishes you as the copyright holder. In principle, you own the copyright to anything you write the moment it's on paper. But, like I said, in practice, if the matter comes under dispute, courts look very favorably on you if you've registered the copyright before infringement occurs. P.S. I'm not a lawyer (and I don't play one on tv:)