My Personal Journey from MIT to GPL

It's really not about advancing ideologies but advancing your software. For software under with a Free license, the source code to any improvements someone else made to your software would have to be distributed along with it. Without it, they could keep any improvements they made to themselves.

So using a Free license provides a tangible, non-ideological benefit to your software, in so far as the source to any improvements will be distributed and can be integrated back in to it to make it better.

The one wrinkle is that the traditional GPL was not designed for situations where the software is never actually distributed -- ie. "web services"/SAAS and the like. In that case, even software under the traditional GPL that companies like, say, Google uses could be improved by them without having to distribute the source, as the software only runs on their servers and is never distributed anywhere.

This is where the AGPL comes in, and why Google forbids using AGPL software inhouse.

This is also why I license all my own software under the AGPL.

Let's put licenses for public software projects into three general categories: permissive, copyleft, and noncommercial. MIT is a classic permissive license. GPLv2 is a classic copyleft license. Prosperity (https://licensezero.com/licenses/prosperity) is a recent noncommercial license.

Heavily simplifying, and ignoring a lot of details and variations:

Permissive licenses allow you to do more or less whatever you please with the software, as long as you make sure that copies of the software you share with others come along with copies of the permissive license terms and the developer's copyright notices.

Copyleft licenses are permissive licenses plus one extra rule: In at least some circumstances, you have to share and license your own software work the same way. When you have to share, and what code you have to share, varies by specific copyleft license.

Noncommercial licenses are permissive licenses plus a different rule: You may not use the software for commercial purposes.

So what's the deal with developers releasing code under copyleft licenses, and then charging individual customers for "commercial licenses"? To understand that, we have to read the licenses in context. It's not just about what the licenses say, but about how that fits into the broader picture of the software industry.

Most companies producing software insist on keeping their software closed, rather than releasing it in the open. That way they can sell access and permission to use it. These companies will not share their work alike. So they intentionally avoid and reject software under copyleft licenses that would require them to do otherwise.

However, sometimes these firms really want to use software under a copyleft license in their products. If possible, they'll often try to buy a license from the developer that allows them to ignore the copyleft rule, so they can have it both ways.

Meanwhile, these firms often use tons and tons of permissively licensed software. They're free to do that, without paying anyone, so long as they follow the rules about copies of license terms and copyright notices.

Hopefully that gives you a broad picture to work from. Good luck with your project.

No, the MIT license requires attribution by including the original copyright notice with any distribution of the software. You can claim credit for the parts you build around it, but you can't claim to have written the MIT-licensed part.