Chapter 1
What Is Software Freedom?

Study of the GNU General Public License (herein, abbreviated as GNU GPL or just GPL) must begin by first considering the broader world of software freedom. The GPL was not created in a vacuum. Rather, it was created to embody and defend a set of principles that were set forth at the founding of the GNU Project and the Free Software Foundation (FSF) – the preeminent organization that upholds, defends and promotes the philosophy of software freedom. A prerequisite for understanding both of the popular versions of the GPL (GPLv2 and GPLv3) and their terms and conditions is a basic understanding of the principles behind them. The GPL family of licenses are unlike nearly all other software licenses in that they are designed to defend and uphold these principles.

1.1 The Free Software Definition

The Free Software Definition is set forth in full on FSF’s website at philosophy/free-sw.html. This section presents an abbreviated version that will focus on the parts that are most pertinent to the GPL.

A particular user has software freedom with respect to a particular program if that user has the following freedoms:

The focus on “a particular user” is particularly pertinent here. It is not uncommon for a subset of a specific program’s user base to have these freedoms, while other users of the same version the program have none or only some of these freedoms. Section 12.2 talks in detail about how this can unfortunately happen even if a program is released under the GPL.

Many people refer to software with these freedoms as “Open Source.” Besides having a different political focus from those who call such software by the name “Free Software”,1, those who call the software “Open Source” are often focused on a side issue. Specifically, user access to the source code of a program is a prerequisite to make use of the freedom to modify. However, the important issue is what freedoms are granted in the license that applies to that source code.

Software freedom is only complete when no restrictions are imposed on how these freedoms are exercised. Specifically, users and programmers can exercise these freedoms noncommercially or commercially. Licenses that grant these freedoms for noncommercial activities but prohibit them for commercial activities are considered non-free. The Open Source Initiative (OSI) (the arbiter of what is considered “Open Source”) also regards such licenses as inconsistent with its “Open Source Definition”.

In general, software for which any of these freedoms are restricted in any way is called “nonfree” software. Some use the term “proprietary software” more or less interchangeably with “nonfree software”. The FSF published a useful explanation of various types of software and how they relate to one another.

Keep in mind that none of the terms “software freedom”, “open source” and “free software” are known to be trademarked or otherwise legally restricted by any organization in any jurisdiction. As such, it’s quite common that these terms are abused and misused by parties who wish to bank on the popularity of software freedom. When one considers using, modifying or redistributing a software package that purports to be Open Source or Free Software, one must verify that the license grants software freedom.

Furthermore, throughout this text, we generally prefer the term “software freedom”, as this is the least ambiguous term available to describe software that meets the Free Software Definition. For example, it is well known and often discussed that the adjective “free” has two unrelated meanings in English: “free as in freedom” and “free as in price”. Meanwhile, the term “open source” is even more confusing, because it appears to refer only to the “freedom to study”, which is merely a subset of one of the four freedoms.

The remainder of this section considers each of each component of software freedom in detail.

1.1.1 The Freedom to Run

The first tenet of software freedom is the user’s fully unfettered right to run the program. The software’s license must permit any conceivable use of the software. Perhaps, for example, the user has discovered an innovative use for a particular program, one that the programmer never could have predicted. Such a use must not be restricted.

It was once rare that this freedom was restricted by even proprietary software; but such is quite common today. Most End User License Agreements (EULAs) that cover most proprietary software typically restrict some types of uses. Such restrictions of any kind are an unacceptable restriction on software freedom.

1.1.2 The Freedom to Change and Modify

Perhaps the most useful right of software freedom is the users’ right to change, modify and adapt the software to suit their needs. Access to the source code and related build and installation scripts are an essential part of this freedom. Without the source code, and the ability to build and install the binary applications from that source, users cannot effectively exercise this freedom.

Programmers directly benefit from this freedom. However, this freedom remains important to users who are not programmers. While it may seem counterintuitive at first, non-programmer users often exercise this freedom indirectly in both commercial and noncommercial settings. For example, users often seek noncommercial help with the software on email lists and in user groups. To make use of such help they must either have the freedom to recruit programmers who might altruistically assist them to modify their software, or to at least follow rote instructions to make basic modifications themselves.

More commonly, users also exercise this freedom commercially. Each user, or group of users, may hire anyone they wish in a competitive free market to modify and change the software. This means that companies have a right to hire anyone they wish to modify their Free Software. Additionally, such companies may contract with other companies to commission software modifications.

1.1.3 The Freedom to Copy and Share

Users share Free Software in a variety of ways. Software freedom advocates work to eliminate a fundamental ethical dilemma of the software age: choosing between obeying a software license and friendship (by giving away a copy of a program to your friend who likes the software you are using). Licenses that respect software freedom, therefore, permit altruistic sharing of software among friends.

The commercial environment also benefits from this freedom. Commercial sharing includes selling copies of Free Software: that is, Free Software can be distributed for any monetary price to anyone. Those who redistribute Free Software commercially also have the freedom to selectively distribute (i.e., you can pick your customers) and to set prices at any level that redistributor sees fit.

Of course, most people get copies of Free Software very cheaply (and sometimes without charge). The competitive free market of Free Software tends to keep prices low and reasonable. However, if someone is willing to pay billions of dollars for one copy of the GNU Compiler Collection, such a sale is completely permitted.

Another common instance of commercial sharing is service-oriented distribution. For example, some distribution vendors provide immediate security and upgrade distribution via a special network service. Such distribution is not necessarily contradictory with software freedom.

(Section 12.2 of this tutorial talks in detail about some common Free Software business models that take advantage of the freedom to share commercially.)

1.1.4 The Freedom to Share Improvements

The freedom to modify and improve is somewhat empty without the freedom to share those improvements. The software freedom community is built on the pillar of altruistic sharing of improved Free Software. Historically it was typical for a Free Software project to sprout a mailing list where improvements would be shared freely among members of the development community.2 Such noncommercial sharing is the primary reason that Free Software thrives.

Commercial sharing of modified Free Software is equally important. For commercial support to exist in a competitive free market, all developers – from single-person contractors to large software companies – must have the freedom to market their services as augmenters of Free Software. All forms of such service marketing must be equally available to all.

For example, selling support services for Free Software is fully permitted. Companies and individuals can offer themselves as “the place to call” when software fails or does not function properly. For such a service to be meaningful, the entity offering that service needs the right to modify and improve the software for the customer to correct any problems that are beyond mere user error.

Software freedom licenses also permit any entity to distribute modified versions of Free Software. Most Free Software programs have a “standard version” that is made available from the primary developers of the software. However, all who have the software have the “freedom to fork” – that is, make available nontrivial modified versions of the software on a permanent or semi-permanent basis. Such freedom is central to vibrant developer and user interaction.

Companies and individuals have the right to make true value-added versions of Free Software. They may use freedom to share improvements to distribute distinct versions of Free Software with different functionality and features. Furthermore, this freedom can be exercised to serve a disenfranchised subset of the user community. If the developers of the standard version refuse to serve the needs of some of the software’s users, other entities have the right to create a long- or short-lived fork to serve that sub-community.

1.2 How Does Software Become Free?

The previous section set forth key freedoms and rights that are referred to as “software freedom”. This section discusses the licensing mechanisms used to enable software freedom. These licensing mechanisms were ultimately created as a community-oriented “answer” to the existing proprietary software licensing mechanisms. Thus, first, consider carefully why proprietary software exists in the first place.

The primary legal regime that applies to software is copyright law. Proprietary software exists at all only because copyright law governs software.3 Copyright law, with respect to software, typically governs copying, modifying, and redistributing that software (For details of this in the USA, see  106 and  117 of Title 17 of the United States Code).4 By law (in the USA and in most other jurisdictions), the copyright holder (most typically, the author) of the work controls how others may copy, modify and/or distribute the work. For proprietary software, these controls are used to prohibit these activities. In addition, proprietary software distributors further impede modification in a practical sense by distributing only binary code and keeping the source code of the software secret.

Copyright is not a natural state, it is a legal construction. In the USA, the Constitution permits, but does not require, the creation of copyright law as federal legislation. Software, since it is an “original work of authorship fixed in any tangible medium of expression ... from which they can be perceived, reproduced, or otherwise communicated, either directly or with the aid of a machine or device” (as stated in 17 USC  102), is thus covered by the statute, and is copyrighted by default.

However, software, in its natural state without copyright, is Free Software. In an imaginary world with no copyright, the rules would be different. In this world, when you received a copy of a program’s source code, there would be no default legal system to restrict you from sharing it with others, making modifications, or redistributing those modified versions.5

Software in the real world is copyrighted by default and is automatically covered by that legal system. However, it is possible to move software out of the domain of the copyright system. A copyright holder can often disclaim their copyright. (For example, under USA copyright law it is possible for a copyright holder to engage in conduct resulting in abandonment of copyright.) If copyright is disclaimed, the software is effectively no longer restricted by copyright law. Software not restricted by copyright is in the “public domain.”

1.2.1 Public Domain Software

In the USA and other countries that are parties to the Berne Convention on Copyright, software is copyrighted automatically by the author when she fixes the software in a tangible medium. In the software world, this usually means typing the source code of the software into a file.

Imagine if authors could truly disclaim those default controls of copyright law. If so, the software is in the public domain — no longer covered by copyright. Since copyright law is the construction allowing for most restrictions on software (i.e., prohibition of copying, modification, and redistribution), removing the software from the copyright system usually yields software freedom for its users.

Carefully note that software truly in the public domain is not licensed in any way. It is confusing to say software is “licensed for the public domain,” or any phrase that implies the copyright holder gave express permission to take actions governed by copyright law.

Copyright holders who state that they are releasing their code into the public domain are effectively renouncing copyright controls on the work. The law gave the copyright holders exclusive controls over the work, and they chose to waive those controls. Software that is, in this sense, in the public domain is conceptualized by the developer as having no copyright and thus no license. The software freedoms discussed in Section 1.1 are all granted because there is no legal system in play to take them away.

Admittedly, a discussion of public domain software is an oversimplified example. Because copyright controls are usually automatically granted and because, in some jurisdictions, some copyright controls cannot be waived (see Section 1.2.4 for further discussion), many copyright holders sometimes incorrectly believe a work has been placed in the public domain. Second, due to aggressive lobbying by the entertainment industry, the “exclusive Right” of copyright, that was supposed to only exist for “Limited Times” according to the USA Constitution, appears to be infinite: simply purchased on the installment plan rather than in whole. Thus, we must assume no works of software will fall into the public domain merely due to the passage of time.

Nevertheless, under USA law it is likely that the typical disclaimers of copyright or public domain dedications we see in the Free Software world would be interpreted by courts as copyright abandonment, leading to a situation in which the user effectively receives a maximum grant of copyright freedoms, similar to a maximally-permissive Free Software license.

The best example of software known to truly be in the public domain is software that is published by the USA government. Under 17 USC 101  105, all works published by the USA Government are not copyrightable in the USA.

1.2.2 Why Copyright Free Software?

If simply disclaiming copyright on software yields Free Software, then it stands to reason that putting software into the public domain is the easiest and most straightforward way to produce Free Software. Indeed, some major Free Software projects have chosen this method for making their software Free. However, most of the Free Software in existence is copyrighted. In most cases (particularly in those of FSF and the GNU Project), this was done due to very careful planning.

Software released into the public domain does grant freedom to those users who receive the standard versions on which the original author disclaimed copyright. However, since the work is not copyrighted, any nontrivial modification made to the work is fully copyrightable.

Free Software released into the public domain initially is Free, and perhaps some who modify the software choose to place their work into the public domain as well. However, over time, some entities will choose to proprietarize their modified versions. The public domain body of software feeds the proprietary software. The public commons disappears, because fewer and fewer entities have an incentive to contribute back to the commons. They know that any of their competitors can proprietarize their enhancements. Over time, almost no interesting work is left in the public domain, because nearly all new work is done by proprietarization.

A legal mechanism is needed to redress this problem. FSF was in fact originally created primarily as a legal entity to defend software freedom, and that work of defending software freedom is a substantial part of its work today. Specifically because of this “embrace, proprietarize and extend” cycle, FSF made a conscious choice to copyright its Free Software, and then license it under “copyleft” terms. Many, including the developers of the kernel named Linux, have chosen to follow this paradigm.

Copyleft is a strategy of utilizing copyright law to pursue the policy goal of fostering and encouraging the equal and inalienable right to copy, share, modify and improve creative works of authorship. Copyleft (as a general term) describes any method that utilizes the copyright system to achieve the aforementioned goal. Copyleft as a concept is usually implemented in the details of a specific copyright license, such as the GNU General Public License (GPL) and the Creative Commons Attribution Share Alike License (the latter of which is the license of this work itself). Copyright holders of creative work can unilaterally implement these licenses for their own works to build communities that collaboratively share and improve those copylefted creative works.

Copyleft uses functional parts of the copyright system to achieve an unusual result (legal protection for free sharing). Copyleft modifies, or “hacks” copyright law, which is usually employed to strengthen the rights of authors or publishers, to strengthen instead the rights of users. Thus, Copyleft is a legal strategy and mechanism to defend, uphold and propagate software freedom. The basic technique of copyleft is as follows: copyright the software, license it under terms that give all the software freedoms, but use the copyright law controls to ensure that all who receive a copy of the software have equal rights and freedom. In essence, copyleft grants freedom, but forbids others to forbid that freedom to anyone else along the distribution and modification chains.

Copyleft’s “reciprocity” or “share and share alike” rule protects both developers, who avoid facing a “prioritized” competitor of their project, and users, who can be sure that they will have all four software freedoms — not only in the present version of the program they use, but in all its future improved versions.

Copyleft is a general concept. Much like ideas for what a computer might do must be implemented by a program that actually does the job, so too must copyleft be implemented in some concrete legal structure. “Share and share alike” is a phrase that is used often enough to explain the concept behind copyleft, but to actually make it work in the real world, a true implementation in legal text must exist, written as a “copyright license”. The GPL implements the concept of copyleft for software-oriented and other functional works of a technical nature. The “CC BY SA” license implements copyleft for works of textual, musical and visual authorship, such as this tutorial.

Copyleft advocates often distinguish between the concept of a “strong copyleft” or a “weak copyleft”. However, “strong vs. weak” copyleft is not a dichotomy, it’s a spectrum. The strongest copylefts strive to the exclusive rights that copyright grants to authors as extensively as possible to maximize software freedom. As a copyleft gets “weaker”, the copyleft license typically makes “trade offs” that might impede software freedom, but reach other tactic goals for the community of users and developers of the work.

In other words, strong copyleft licenses place the more requirements on how “the work” is licensed. The unit of copyright law is “the work”. In that sense, the “work” referenced by the licenses is anything that can be copyrighted or will be subject to the terms of copyright law. Strong copyleft licenses exercise their scope fully. Anything which is “a work” or a “work based on a work” licensed under a strong copyleft is subject to its requirements, including the requirement of complete, corresponding source code6. Thus, copyleft licenses, particularly strong ones, seek to ensure the same license covers every version of “work based on the work”, as recognized by local copyright law, and thereby achieve the specific strategic policy aim of ensuring software freedom for all users, developers, authors, and readers who encounter the copylefted work.

1.2.3 Software and Non-Copyright Legal Regimes

The use, modification and distribution of software, like many endeavors, simultaneously interacts with multiple different legal regimes. As was noted early via footnotes, copyright is merely the most common way to restrict users’ rights to copy, share, modify and/or redistribute software. However, proprietary software licenses typically use every mechanism available to subjugate users. For example:

Thus, most proprietary software restricts users via multiple interlocking legal and technological means. Any license that truly respect the software freedom of all users must not only grant appropriate copyright permissions, but also prevent restrictions from other legal and technological means like those listed above.

1.2.4 Non-USA Copyright Regimes

Generally speaking, copyright law operates similarly enough in countries that have signed the Berne Convention on Copyright, and software freedom licenses have generally taken advantage of this international standardization of copyright law. However, copyright law does differ from country to country, and commonly, software freedom licenses like the GPL must be considered under the copyright law in the jurisdiction where any licensing dispute occurs.

Those who are most familiar with the USA’s system of copyright often are surprised to learn that there are certain copyright controls that cannot be waived nor disclaimed. Specifically, many copyright regimes outside the USA recognize a concept of moral rights of authors. Typically, moral rights are fully compatible with respecting software freedom, as they are usually centered around controls that software freedom licenses generally respect, such as the right of an authors to require proper attribution for their work.

1.3 A Community of Equality

The previous section described the principles of software freedom, a brief introduction to mechanisms that typically block these freedoms, and the simplest ways that copyright holders might grant those freedoms to their users for their copyrighted works of software. The previous section also introduced the idea of copyleft: a licensing mechanism to use copyright to not only grant software freedom to users, but also to uphold those rights against those who might seek to curtail them.

Copyleft, as defined in  1.2.2, is a general term for this mechanism. The remainder of this text will discuss details of various real-world implementations of copyleft – most notably, the GPL.

This discussion begins first with some general explanation of what the GPL is able to do in software development communities. After that brief discussion in this section, deeper discussion of how GPL accomplishes this in practice follows in the next chapter.

Simply put, though, the GPL ultimately creates a community of equality for both business and noncommercial users.

1.3.1 The Noncommercial Community

A GPL’d code base becomes a center of a vibrant development and user community. Traditionally, volunteers, operating noncommercially out of keen interest or “scratch an itch” motivations, produce initial versions of a GPL’d system. Because of the efficient distribution channels of the Internet, any useful GPL’d system is adopted quickly by noncommercial users.

Fundamentally, the early release and quick distribution of the software gives birth to a thriving noncommercial community. Users and developers begin sharing bug reports and bug fixes across a shared intellectual commons. Users can trust the developers, because they know that if the developers fail to address their needs or abandon the project, the GPL ensures that someone else has the right to pick up development. Developers know that the users cannot redistribute their software without passing along the rights granted by the GPL, so they are assured that every one of their users is treated equally.

Because of the symmetry and fairness inherent in GPL’d distribution, nearly every GPL’d package in existence has a vibrant noncommercial user and developer base.

1.3.2 The Commercial Community

By the same token, nearly all established GPL’d software systems have a vibrant commercial community. Nearly every GPL’d system that has gained wide adoption from noncommercial users and developers eventually begins to fuel a commercial system around that software.

For example, consider the Samba file server system that allows Unix-like systems (including GNU/Linux) to serve files to Microsoft Windows systems. Two graduate students originally developed Samba in their spare time and it was deployed noncommercially in academic environments.9 However, very soon for-profit companies discovered that the software could work for them as well, and their system administrators began to use it in place of Microsoft Windows NT file-servers. This served to lower the cost of running such servers by orders of magnitude. There was suddenly room in Windows file-server budgets to hire contractors to improve Samba. Some of the first people hired to do such work were those same two graduate students who originally developed the software.

The noncommercial users, however, were not concerned when these two fellows began collecting paychecks off of their GPL’d work. They knew that because of the nature of the GPL that improvements that were distributed in the commercial environment could easily be folded back into the standard version. Companies are not permitted to proprietarize Samba, so the noncommercial users, and even other commercial users are safe in the knowledge that the software freedom ensured by the GPL will remain protected.

Commercial developers also work in concert with noncommercial developers. Those two now-long-since graduated students continue to contribute to Samba altruistically, but also get paid work doing it. Priorities change when a client is in the mix, but all the code is contributed back to the standard version. Meanwhile, many other individuals have gotten involved noncommercially as developers, because they want to “cut their teeth on Free Software,” or because the problems interest them. When they get good at it, perhaps they will move on to another project, or perhaps they will become commercial developers of the software themselves.

No party is a threat to another in the GPL software scenario because everyone is on equal ground. The GPL protects rights of the commercial and noncommercial contributors and users equally. The GPL creates trust, because it is a level playing field for all.

1.3.3 Law Analogy

In his introduction to Stallman’s Free Software, Free Society, Lawrence Lessig draws an interesting analogy between the law and Free Software. He argues that the laws of a free society must be protected much like the GPL protects software. So that I might do true justice to Lessig’s argument, I quote it verbatim:

A “free society” is regulated by law. But there are limits that any free society places on this regulation through law: No society that kept its laws secret could ever be called free. No government that hid its regulations from the regulated could ever stand in our tradition. Law controls. But it does so justly only when visibly. And law is visible only when its terms are knowable and controllable by those it regulates, or by the agents of those it regulates (lawyers, legislatures).

This condition on law extends beyond the work of a legislature. Think about the practice of law in American courts. Lawyers are hired by their clients to advance their clients’ interests. Sometimes that interest is advanced through litigation. In the course of this litigation, lawyers write briefs. These briefs in turn affect opinions written by judges. These opinions decide who wins a particular case, or whether a certain law can stand consistently with a constitution.

All the material in this process is free in the sense that Stallman means. Legal briefs are open and free for others to use. The arguments are transparent (which is different from saying they are good), and the reasoning can be taken without the permission of the original lawyers. The opinions they produce can be quoted in later briefs. They can be copied and integrated into another brief or opinion. The “source code” for American law is by design, and by principle, open and free for anyone to take. And take lawyers do—for it is a measure of a great brief that it achieves its creativity through the reuse of what happened before. The source is free; creativity and an economy is built upon it.

This economy of free code (and here I mean free legal code) doesn’t starve lawyers. Law firms have enough incentive to produce great briefs even though the stuff they build can be taken and copied by anyone else. The lawyer is a craftsman; his or her product is public. Yet the crafting is not charity. Lawyers get paid; the public doesn’t demand such work without price. Instead this economy flourishes, with later work added to the earlier.

We could imagine a legal practice that was different — briefs and arguments that were kept secret; rulings that announced a result but not the reasoning. Laws that were kept by the police but published to no one else. Regulation that operated without explaining its rule.

We could imagine this society, but we could not imagine calling it “free.” Whether or not the incentives in such a society would be better or more efficiently allocated, such a society could not be known as free. The ideals of freedom, of life within a free society, demand more than efficient application. Instead, openness and transparency are the constraints within which a legal system gets built, not options to be added if convenient to the leaders. Life governed by software code should be no less.

Code writing is not litigation. It is better, richer, more productive. But the law is an obvious instance of how creativity and incentives do not depend upon perfect control over the products created. Like jazz, or novels, or architecture, the law gets built upon the work that went before. This adding and changing is what creativity always is. And a free society is one that assures that its most important resources remain free in just this sense.10

In essence, lawyers are paid to service the shared commons of legal infrastructure. Few citizens defend themselves in court or write their own briefs (even though they are legally permitted to do so) because everyone would prefer to have an expert do that job.

The Free Software economy is a market ripe for experts. It functions similarly to other well established professional fields like the law. The GPL, in turn, serves as the legal scaffolding that permits the creation of this vibrant commercial and noncommercial Free Software economy.

1The political differences between the Free Software Movement and the Open Source Movement are documented on FSF’s Web site at

2This is still commonly the case, though today there are additional ways of sharing Free Software.

3This statement is admittedly an oversimplification. Patents and trade secrets can cover software and make it effectively non-Free, and one can contract away their rights and freedoms regarding software, or source code can be practically obscured in binary-only distribution without reliance on any legal system. However, the primary control mechanism for software is copyright, and therefore this section focuses on how copyright restrictions make software proprietary.

4Copyright law in general also governs “public performance” of copyrighted works. There is no generally agreed definition for public performance of software and both GPLv2 and GPLv3 do not restrict public performance.

5Note that this is again an oversimplification; the complexities with this argument are discussed in Section 1.2.3.

6Copyleft communities’ use of the term “strong copyleft” is undoubtedly imprecise. For example, most will call the GNU GPL a “strong copyleft” license, even though the GPL itself has various exceptions, such as the GPLv3’s system library exception written into the text of the license itself. Furthermore, the copyleft community continues to debate where the a license cross the line from “strong copyleft” to “license that fails to respect software freedom”, although ultimately these debates are actually regarding whether the license fits Free Software definition at all.

7See  6, 7.5, 9.14 for more discussion on how the patent system interacts with copyleft, and read Richard M. Stallman’s essay, Let’s Limit the Effect of Software Patents, Since We Can’t Eliminate Them for more information on the problems these patents present to society.

8See  9.5 for more information on how GPL deals with this issue.

9See Andrew Tridgell’s “A bit of history and a bit of fun”

10This quotation is Copyright 2002, Lawrence Lessig. It is licensed under the terms of the “Attribution License” version 1.0 or any later version as published by Creative Commons.