Chapter 2
A Tale of Two Copyleft Licenses

While determining the proper methodology and criteria to yield an accurate count remains difficult, the GPL is generally considered one of the most widely used Free Software licenses. For most of its history — for 16 years from June 1991 to June 2007 — there was really only one version of the GPL, version 2.

However, the GPL had both earlier versions before version 2, and, more well known, a revision to version 3.

2.1 Historical Motivations for the General Public License

The earliest license to grant software freedom was likely the Berkeley Software Distribution (“BSD”) license. This license is typical of what are often called lax, highly permissive licenses. Not unlike software in the public domain, these non-copyleft licenses (usually) grant software freedom to users, but they do not go to any effort to uphold that software freedom for users. The so-called “downstream” (those who receive the software and then build new things based on that software) can restrict the software and distribute further.

The GNU’s Not Unix (“GNU”) project, which Richard M. Stallman (“RMS”) founded in 1984 to make a complete Unix-compatible operating system implementation that assured software freedom for all. However, RMS saw that using a license that gave but did not assure software freedom would be counter to the goals of the GNU Project. RMS invented “copyleft” as an answer to that problem, and began using various copyleft licenses for the early GNU Project programs.1

2.2 Proto-GPLs And Their Impact

The earliest copyleft licenses were specific to various GNU programs. For example, The Emacs General Public License was likely the first copyleft license ever published. Interesting to note that even this earliest copyleft license contains a version of the well-known GPL copyleft clause:

You may modify your copy or copies of GNU Emacs …provided that you also …cause the whole of any work that you distribute or publish, that in whole or in part contains or is a derivative of GNU Emacs or any part thereof, to be licensed at no charge to all third parties on terms identical to those contained in this License Agreement.

This simply stated clause is the fundamental innovation of copyleft. Specifically, copyleft uses the copyright holders’ controls on permission to modify the work to add a conditional requirement. Namely, downstream users may only have permission to modify the work if they pass along the same permissions on the modified version that came originally to them.

These original program-specific proto-GPLs give an interesting window into the central ideas and development of copyleft. In particular, reviewing them shows how the text of the GPL we know has evolved to address more of the issues discussed earlier in  1.2.3.

2.3 The GNU General Public License, Version 1

In January 1989, the FSF announced that the GPL had been converted into a “subroutine” that could be reused not just for all FSF-copyrighted programs, but also by anyone else. As the FSF claimed in its announcement of the GPLv1:2

To make it easier to copyleft programs, we have been improving on the legalbol architecture of the General Public License to produce a new version that serves as a general-purpose subroutine: it can apply to any program without modification, no matter who is publishing it.

This, like many inventive ideas, seems somewhat obvious in retrospect. But, the FSF had some bright people and access to good lawyers when it started. It took almost five years from the first copyleft licenses to get to a generalized, reusable GPLv1. In the context and mindset of the 1980s, this is not surprising. The idea of reusable licensing infrastructure was not only uncommon, it was virtually nonexistent! Even the early BSD licenses were simply copied and rewritten slightly for each new use.3 The GPLv1’s innovation of reusable licensing infrastructure, an obvious fact today, was indeed a novel invention for its day.4

2.4 The GNU General Public License, Version 2

The GPLv2 was released two and a half years after GPLv1, and over the following sixteen years, it became the standard for copyleft licensing until the release of GPLv3 in 2007 (discussed in more detail in the next section).

While this tutorial does not discuss the terms of GPLv1 in detail, it is worth noting below the three key changes that GPLv2 brought:

The next chapter discusses GPLv2 in full detail, and readers who wish to dive into the section-by-section discussion of the GPL should jump ahead now to that chapter. However, the most interesting fact to note here is how GPLv2 was published with little fanfare and limited commentary. This contrasts greatly with the creation of GPLv3.

2.5 The GNU General Public License, Version 3

RMS began drafting GPLv2.2 in mid-2002, and FSF ran a few discussion groups during that era about new text of that license. However, rampant violations of the GPL required more immediate attention of FSF’s licensing staff, and as such, much of the early 2000’s was spent doing GPL enforcement work.5 In 2006, FSF began in earnest drafting work for GPLv3.

The GPLv3 process began in earnest in January 2006. It became clear that many provisions of the GPL could benefit from modification to fit new circumstances and to reflect what the entire community learned from experience with version 2. Given the scale of revision it seems proper to approach the work through public discussion in a transparent and accessible manner.

The GPLv3 process continued through June 2007, culminating in publication of GPLv3 and LGPLv3 on 29 June 2007, AGPLv3 on 19 November 2007, and the GCC Runtime Library Exception on 27 January 2009.

All told, four discussion drafts of GPLv3, two discussion drafts of LGPLv3 and two discussion drafts of AGPLv3 were published and discussed. Ultimately, FSF remained the final arbiter and publisher of the licenses, and RMS himself their primary author, but input was sought from many parties, and these licenses do admittedly look and read more like legislation as a result. Nevertheless, all of the “v3” group are substantially better and improved licenses.

GPLv3 and its terms are discussed in detail in Chapter 9.

2.6 The Innovation of Optional “Or Any Later” Version

An interesting fact of all GPL licenses is that there are ultimately multiple choices for use of the license. The FSF is the primary steward of GPL (as discussed later in  8.1 and  9.17). However, those who wish to license works under GPL are not required to automatically accept changes made by the FSF for their own copyrighted works.

Each licensor may chose three different methods of licensing, as follows:

Oddly, this flexibility has received (in the opinion of the authors, undue) criticism, primarily because of the complex and oft-debated notion of “license compatibility” (which is explained in detail in  9.10). Copyleft licenses are generally incompatible with each other, because the details of how they implement copyleft differs. Specifically, copyleft works only because of its requirement that downstream licensors use the same license for combined and modified works. As such, software licensed under the terms of “GPLv2-only” cannot be combined with works licensed “GPLv3-or-later”. This is admittedly a frustrating outcome.

Other copyleft licenses that appeared after GPL, such as the Creative Commons “Attribution-Share Alike” licenses, the Eclipse Public License and the Mozilla Public License require all copyright holders choosing to use any version of those licenses to automatically allow use of their copyrighted works under new versions.7 Of course, Creative Commons, the Eclipse Foundation, and the Mozilla Foundation (like the FSF) have generally served as excellent stewards of their licenses. Copyright holders using those licenses seems to find it acceptable to fully delegate all future licensing decisions for their copyrights to these organizations without a second thought.

However, note that FSF gives herein the control of copyright holders to decide whether or not to implicitly trust the FSF in its work of drafting future GPL versions. The FSF, for its part, does encourage copyright holders to chose by default “GPLvX-or-later” (where X is the most recent version of the GPL published by the FSF). However, the FSF does not mandate that a choice to use any GPL requires a copyright holder ceding its authority for future licensing decisions to the FSF. In fact, the FSF considered this possibility for GPLv3 and chose not to do so, instead opting for the third-party steward designation clause discussed in Section 9.17.

2.7 Complexities of Two Simultaneously Popular Copylefts

Obviously most GPL advocates would prefer widespread migration to GPLv3, and many newly formed projects who seek a copyleft license tend to choose a GPLv3-based license. However, many existing copylefted projects continue with GPLv2-only or GPLv2-or-later as their default license.

While GPLv3 introduces many improvements — many of which were designed to increase adoption by for-profit companies — GPLv2 remains a widely used and extremely popular license. The GPLv2 is, no doubt, a good and useful license.

However, unlike GPLv1 before it, GPLv2 remains an integral part of the copyleft licensing infrastructure. As such, those who seek to have expertise in current topics of copyleft licensing need to study both the GPLv2 and GPLv3 family of licenses.

Furthermore, GPLv3 is more easily understood by first studying GPLv2. This is not only because of their chronological order, but also because much of the discussion material available for GPLv3 tends to talk about GPLv3 in contrast to GPLv2. As such, a strong understanding of GPLv2 helps in understanding most of the third-party material found regarding GPLv3. Thus, the following chapter begins a deep discussion of GPLv2.

1RMS writes more fully about this topic in his essay entitled simply The GNU Project. For those who want to hear the story in his own voice, speech recordings of his talk, The Free Software Movement and the GNU/Linux Operating System are also widely available

2The announcement of GPLv1 was published in the GNU’s Bulletin, vol 1, number 6 dated January 1989. (Thanks very much to Andy Tai for his consolidation of research on the history of the pre-v1 GPL’s.)

3It remains an interesting accident of history that the early BSD problematic “advertising clause” (discussion of which is somewhat beyond the scope of this tutorial) lives on into current day, simply because while the University of California at Berkeley gave unilateral permission to remove the clause from its copyrighted works, others who adapted the BSD license with their own names in place of UC-Berkeley’s never have.

4We’re all just grateful that the FSF also opposes business method patents, since the FSF’s patent on a “method for reusable licensing infrastructure” would have not expired until 2006!

5More on GPL enforcement is discussed in Part II of this tutorial.

6The shorthand of “GPLX+” is also popular for this situation. The authors of this tutorial prefer “-or-later” syntax, because it (a) mirrors the words “or” and “later from the licensing statement, (b) the X+ doesn’t make it abundantly clear that X is clearly included as a license option and (c) the + symbol has other uses in computing (such as with regular expressions) that mean something different.

7CC-BY-SA-2.0 and greater only permit licensing of adaptations under future versions; 1.0 did not have any accomodation for future version compatibility.