Two Kinds of “Dual Licensing”a license operator and a business model
This post is part of a series, Overloaded.
“Dual licensing” is the inclusive-or operator for free, public license terms. It lets us glue two forms together and stick them to one project.
“Dual licensing” is also a business model involving not-free, one-off licenses. It’s one of the oldest commercial models for “open”.
These meanings are just close and far enough to make “dual licensing” more a question in itself than any useful answer, absent heaps of clarifying context. And various kinds of dual licensing are common enough to trip up nearly everyone on their path through the industry, somewhere along the line.
If I say my new project is “dual-licensed”, all you’re given to know is that more than one set of license terms is potentially involved. Compared to “knock yourself out, we’re MIT!”, “it’s dual-licensed” is the “It’s Complicated” of software. Even if the picture isn’t really that complicated. Even though half the complexity is usually narrowing down which “dual licensing” is involved.
Slice through this confusion by distinguishing two kinds of dual licensing: choice-of-terms and free-and-paid.
Choice-of-Terms Dual Licensing
Choice-of-open dual-licensed projects offer everyone the choice of one or more free-of-charge licenses, like “MIT or GPLv2” or “BSD or Apache 2”.
All the licenses are costless and public, but they are not necessarily “open”. A choice-of-terms dual-licensed project could also offer a choice of more restrictive terms, like “CC-BY-NC or CC-BY-NoDerivs” or “PolyForm Small Business or PolyForm Free Trial”.
Regardless of what kinds of licenses stand on offer, if you do what’s required by one of them, you aren’t infringing copyright in the project, even if you’re not doing what’s required by another. In practice, that means you get the most that each license allows, the union set. Offering a choice of free, public licenses only means more permission.
A project licensed “MIT or GPLv2” is in essence MIT licensed. MIT allows more than GPLv2 does, so anyone charged with a violation will show compliance with the more permissive terms. Similarly, a project licensed “LGPLv2 or GPLv2” would in essence be LGPL-licensed. LGPL is a “weaker”—more permissive—copyleft license than GPL. Expressing these kinds of choices is practically pointless, which is why you won’t see it much.
Why would a project ever want this complication?
Some projects offer choice-of-open intentionally, to avoid “compatibility” problems with other licenses, especially copyleft ones. The Free Software Foundation has long said that Apache 2-licensed code can’t be included and distributed under GPLv2 terms, but can be under GPLv3—that Apache 2 is “compatible with” GPLv3 but “incompatible with” GPLv2. So the Rust people, who wanted to make sure their code could be used anywhere, offered both MIT, which FSF admits is “GPLv2-compatible”, and Apache 2, which nearly everyone admits has clearer patent language. If you work at a big company that gets sued for patent infringement using Rust, you can “choose” Apache 2 and its patent grant. If you’re developing a GPLv2 project and want to reuse some Rust code, you can opt for MIT and avoid the debate about Apache 2.
Some projects end up choice-of-open dual licensing when they license old releases under some new set of terms. For example, projects upgrading from GPLv2 to GPLv3 by getting permission from all copyright holders don’t replace or take back the GPLv2 licenses for their old releases. They merely license those releases under GPLv3, as well. Others building on those old releases can then comply with copyleft by offering and licensing their code under GPLv3, rather than GPLv2. The GPLv2 licenses for those releases specifically require GPLv2, but users can ignore GPLv2’s requirements if they comply with GPLv3’s.
I’ve sometimes heard choice-of-terms dual licensing called “multi-licensing”. “Multi” is so close to “dual” in meaning that it really doesn’t get us anywhere. We could split hairs about “there are two licenses” versus “there’s more than one license”, but neither says anything about the kinds of licenses involved or any differences between them. “Multi” doesn’t relieve the overloading.
Free-and-Paid Dual Licensing
Free-and-paid dual-licensed projects come with free-of-charge licenses that permit everyone some, but not all, uses. Would-be customers can then buy licenses that allow some or all of what the free terms don’t.
The free license might allow noncommercial use, while paid licenses cover use in business. Or the free license might require “sharing alike”, while paid licenses allow use in closed products and services. Anything the free license withholds permission to do, the paid licenses can permit for a price.
The canonical example of free-and-paid dual licensing in software remains MySQL. If you can meet the requirements of the project’s GPLv2 copyleft license or the extra permission they give for FOSS, you don’t need to pay Oracle anything. If you want to distribute MySQL as part of a closed project, or to make changes to MySQL and not share them under GPLv2 with your users, you can buy an “OEM” license to do that and ignore GPLv2.
The Free Software Foundation has long called this “selling exceptions”, but as far as I can tell, we’re still far more likely to read and hear “dual licensing”, even specifically for the free-and-paid kind.
I personally tried using “public-private licensing”. That speaks right to the heart of the distinction. But it’s also double-stuffed with jargon, way too late, and objectively doomed.
Other Kinds, Other Ways
This isn’t the only way to divide up all we call “dual licensing”. But in my experience, it’s the most useful way that maps to short, approachable terms. As business and licensing practices change, there may come a day when a different heuristic takes over. Language is ever a ship at sea.
In the meantime, life doesn’t owe us a reality that’s fun or easy to think about. Edge cases will bust the distinctions I’ve made and coupled here—free-of-charge versus paid, public versus private—or blur them. We’ve already seen licenses that apply to everyone, automatically, so long as they send money or give something else in return, on their own—free, public license offers, rather than free, public licenses. We’ve also seen terms that apply to one and all…except particular people or organizations. But not many. Not yet.
This isn’t science. It’s tactics. The overloading of “dual licensing” has charged us tolls for decades now. Spreading that load between choice-of-terms and free-paid makes things understandable and actionable again.
Your thoughts and feedback are always welcome by e-mail.