RMS was the primary author of GPLv3, but he listened to feedback from all

sorts of individuals and even for-profit companies.  Nevertheless, in

attempting to understand GPLv3 after the fact, the materials available from

the GPLv3 process have a somewhat ``drinking from the firehose'' effect.

This chapter seeks to explain GPLv3 to newcomers, who perhaps are familiar

with GPLv2 and who did not participate in the GPLv3 process.

Those who wish to drink from the firehose and take a diachronic approach to

GPLv3 study by reading the step-by-step public drafting process of the GPLv3 (which

occurred from Monday 16 January 2006 through Monday 19 November 2007) should

visit \url{http://gplv3.fsf.org/}.

\section{Understanding GPLv3 As An Upgraded GPLv2}

Ultimately, GPLv2 and GPLv3 co-exist as active licenses in regular use.  As

discussed in Chapter~\ref{tale-of-two-copylefts}, GPLv1 was never regularly

used alongside GPLv2.  However, given GPLv2's widespread popularity and

existing longevity by the time GPLv3 was published, it is not surprising that

some licensors still prefer GPLv2-only or GPLv2-or-later.  GPLv3 gained major

adoption by many projects, old and new, but many projects have not upgraded

due to (in some cases) mere laziness and (in other cases) policy preference

for some of GPLv2's terms and/or policy opposition to GPLv3's terms.

Given this ``two GPLs world'' is reality, it makes sense to consider GPLv3 in

terms of how it differs from GPLv2.  Also, most of the best GPL experts in

the world must deal regularly with both licenses, and admittedly have decades

of experience with GPLv2 while the most experience with GPLv3 that's possible

is by default less than a decade.  These two factors usually cause even new

students of GPL to start with GPLv2 and move on to GPLv3, and this tutorial

follows that pattern.

Overall, the changes made in GPLv3 admittedly \textit{increased} the

complexity of the license.  The FSF stated at the start of the GPLv3 process

that they would have liked to oblige those who have asked for a simpler and

shorter GPL\@.  Ultimately, the FSF gave priority to making GPLv3 a better

copyleft license in the spirit of past GPL's.  Obsession for concision should

never trump software freedom.

The FSF had many different, important goals in seeking to upgrade to GPLv3.

However, one important goal that is often lost in the discussion of policy

minutia is a rather simple but important issue.  Namely, FSF sought to assure

that GPLv3 was more easily internationalized than GPLv2.  In particular, the

FSF sought to ease interpretation of GPL in other countries by replacement of

USA-centric\footnote{See Section~\ref{non-usa-copyright} of this tutorial for

  a brief discussion about non-USA copyright systems.}  copyright phrases and

wording with neutral terminology rooted in description of behavior rather

than specific statute.  As can be seen in the section-by-section discussion of

GPLv3 that follows, nearly every section had changes related to issues of

internationalization.

\section{GPLv3~\S0: Giving In On ``Defined Terms''}

\label{GPLv3s0}

One of lawyers' most common complaints about GPLv2 is that defined terms in

the document appear throughout.  Most licenses define terms up-front.

However, the GPL was always designed both as a document that should be easily

understood both by lawyers and by software developers: it is a document

designed to give freedom to software developers and users, and therefore it

should be comprehensible to that constituency.

Interestingly enough, one coauthor of this tutorial who is both a lawyer and

a developer pointed out that in law school, she understood defined terms more

quickly than other law students precisely because of her programming

background.  For developers, having \verb0#define0 (in the C programming

language) or other types of constants and/or macros that automatically expand

in the place where they are used is second nature.  As such, adding a defined

terms section was not terribly problematic for developers, and thus GPLv3

adds one.  Most of these defined terms are somewhat straightforward and bring

forward better worded definitions from GPLv2.  Herein, this tutorial

discusses a few of the new ones.

GPLv3~\S0 includes definitions of five new terms not found in any form in

GPLv2: ``modify'' ``covered work'', ``propagate'', ``convey'', and

``Appropriate Legal Notices''. 

\subsection{Modify and the Work Based on the Program}

%  FIXME: I think we actually need to research the claim below that

%  ``derivative work'' as a term is unique to USA copyright law.  I have

%  heard German lawyers, for example, use the term extensively.  Is it also a

%  term perhaps under German law?  -- bkuhn

GPLv2 included a defined term, ``work based on the Program'', but also used

the term ``modify'' and ``based on'' throughout the license.  GPLv2's ``work

based on the Program'' definition made use of a legal term of art,

``derivative work'', which is peculiar to USA copyright

law.\footnote{(Ironically, most criticism of USA-specific legal

terminology in GPLv2's ``work based on the Program'' definition historically

came not primarily from readers outside the USA, but from those within

it.  The FSF noted in that it did not generally agree with these

  views, and expressed puzzlement by the energy with which they were

  expressed, given the existence of many other, more difficult legal issues

  implicated by the GPL.  Nevertheless, the FSF argued that it made sense to

  eliminate usage of local copyright terminology to good effect.}  GPLv2

always sought to cover all rights governed by relevant copyright law, in the

USA and elsewhere.

Even though differently-labeled concepts corresponding to the

derivative work are recognized in all copyright law systems, these

counterpart concepts might differ to some degree in scope and breadth from

the USA derivative work.  GPLv3 therefore takes the task of

internationalizing the license further by removing references to derivative

works and by providing a more globally useful definition.

GPLv3 drops all reference to USA ``derivative works'' and returns

to the base concept only: GPL covers the licensed work and all works where

copyright permission from the licensed work's copyright holder.

The new definitions returns to the common elements of copyright law.  Copyright

holders of works of software have the exclusive right to form new works by

modification of the original --- a right that may be expressed in various

ways in different legal systems.  GPLv3 operates to grant this right to

successive generations of users (particularly through the copyleft conditions

set forth in GPLv3~\S5, as described later in this tutorial in its

\S~\ref{GPLv3s5}).  Here in GPLv3~\S0, ``modify'' refers to basic copyright

rights, and then this definition of ``modify'' is used to define ``modified

version of'' and ``work based on'' as synonyms.

\subsection{The Covered Work}

GPLv3 uses a common license drafting technique of building upon simpler

definitions to make complex ones.  The Program is a defined term found

throughout GPLv2, and the word ``covered'' and the phrase ``covered by this

license'' are used in tandem with the Program in GPLv2, but not as part of a

definition.  GPLv3 offers a single term ``covered work'', which enables some

of the wording in GPLv3 to be simpler and clearer than its GPLv2

counterparts.

Next, to avoid locking GPLv3 into specific copyright statues, the GPLv3

defines two terms that are otherwise exotic to the language of international

copyright.

\subsection{Propagate}

To ``propagate'' a work covered by the license means any activity in a locale

that requires permission of copyright holders in that locale's legal system.

However, personal use or modification for personal use are activities explicitly

excluded from ``propagation'' \textit{regardless} of domestic copyright law.

The term ``propagate'' serves two purposes.  First, ``propagate'' provides a

simple and convenient means for distinguishing between the kinds of uses of a

work that GPL imposes conditions on and the kinds of uses that GPL does not

(for the most part) impose conditions on.

Second, ``propagate'' helps globalize GPL in its wording and effect:

``derivative work'' was in fact not the only term commonly used by local

copyright statutes.  A term like ``distribute'' (or its equivalent in

languages other than English) is also used in several national copyright

statutes.  Practical experience with GPLv2 revealed the awkwardness of using

the term ``distribution'' in a license intended for global use: the scope of

``distribution'' in the copyright context can differ from country to country.

The GPL never necessarily intended the specific meaning of ``distribution''

that exists under USA (or any other country's) copyright law.

Indeed, even within a single country and language, the term distribution may

be ambiguous; as a legal term of art, distribution varies significantly in

meaning among those countries that recognize it.  For example, comments

during GPLv3's drafting process indicated that in at least one country,

distribution may not include network transfers of software but may include

interdepartmental transfers of physical copies within an organization.

Meanwhile, the copyright laws of many countries, as well as certain

international copyright treaties, recognize ``making available to the

public'' or ``communication to the public'' as one of the exclusive rights of

copyright holders.

Therefore, the GPLv3 defines the term ``propagate'' by reference to activities

that require permission under ``applicable copyright law'', but excludes

execution and private modification from the definition.  GPLv3's definition

also gives examples of activities that may be included within ``propagation''

but it also makes clear that, under the copyright laws of a given country,

``propagation'' may include other activities as well.

Thus, propagation is defined by behavior, and not by categories drawn from

some particular national copyright statute.  This helps not only with

internationalization, but also factually-based terminology aids in

developers' and users' understanding of the GPL\@.

As a further benefit, because ``propagation'' includes all

exclusive rights granted under any particular copyright regime, the term

automatically  accounts for all exclusive rights under that regime.

\subsection{Convey}

Next, GPLv3 defines a subset of propagate --- ``convey''.

Conveying includes activities that constitute propagation of copies to

others.  As with the definition of propagate, GPLv3 thus addresses transfers

of copies of software in behavioral rather than statutory terms.  

Any propagation that enables other parties to receive or make copies of the

work, is called ``conveying''.  Usually, conveying is the activity that

triggers most of the other obligations of GPLv3.

\subsection{Appropriate Legal Notices}

GPLv2 used the term ``appropriate copyright notice and disclaimer of

GPLv2 and other licenses that grant software freedom showed throughout the

1990s that the scope of types of notices that need preservation upon

conveyance were more broad that merely the copyright notices.  The

Appropriate Legal Notice definition consolidates the material that GPLv2

traditionally required preserved into one definition.

\subsection{Other Defined Terms}

Note finally that not all defined terms in GPLv3 appear in GPLv3~\S0.

Specifically, those defined terms that are confined in use to a single

section are defined in the section in which they are used, and GPLv3~\S1

contains those definitions focused on source code.  In this tutorial, those

defined terms are discussed in the section where they are defined and/or

used.

\section{GPLv3~\S1: Understanding CCS}

\label{GPLv3s1}

Ensuring that users have the source code to the software they receive and the

freedom to modify remains the paramount right embodied in the Free Software

Definition (found in \S~\ref{Free Software Definition} of this tutorial).  As

such, GPLv3~\S1 is likely one of the most important sections of GPLv3, as it

contains all the defined terms related to this important software freedom.

\subsection{Source Code Definition}

First, GPLv3~\S1 retains GPLv2's definition of ``source code'' and adds an

explicit definition of ``object code'' as ``any non-source version of a

work''.  Object code is not restricted to a narrow technical meaning and is

understood broadly to include any form of the work other than the preferred

form for making modifications to it.  Object code therefore includes any kind

of transformed version of source code, such as bytecode or minified

Javascript.  The definition of object code also ensures that licensees cannot

escape their obligations under the GPL by resorting to shrouded source or

obfuscated programming.

\subsection{CCS Definition}

\label{CCS Definition}

The definition of CCS,\footnote{Note that the preferred term for those who

  work regularly with both GPLv2 and GPLv3 is ``Complete Corresponding

  Source'', abbreviated to ``CCS''.  Admittedly, the word ``complete'' no

  longer appears in GPLv3 (which uses the word ``all'' instead).  However,

  both GPLv2 and the early drafts of GPLv3 itself used the word ``complete'',

  and early GPLv3 drafts even called this defined term ``Complete

  Corresponding Source''.  Meanwhile, use of the acronym ``CCS'' (sometimes,

  ``C\&CS'') was so widespread among GPL enforcers that its use continues

  even though GPLv3-focused experts tend to say just the defined term of

  ``Corresponding Source''.} or, as GPLv3 officially calls it,

``Corresponding Source'' in GPLv3~\S1\P4 is possibly the most complex

definition in the license.

The CCS definition is broad so as to protect users' exercise of their rights

under the GPL\@.  The definition includes with particular examples to remove

any doubt that they are to be considered CCS\@.  GPLv3 seeks to make it

completely clear that a licensee cannot avoid complying with the requirements

of the GPL by dynamically linking a subprogram component to the original

version of a program.  The example also clarifies that the shared libraries

and dynamically linked subprograms that are included in Corresponding Source

are those that the work is ``specifically'' designed to require, which

clarifies that they do not include libraries invoked by the work that can be

readily substituted by other existing implementations.  While copyleft

advocates never doubted this was required under GPLv2's definition of CCS,

GPLv3 makes it abundantly clear with an extra example.

The GPL, as always, seeks to ensure users are truly in a position to install and

run their modified versions of the program; the CCS definition is designed to

be expansive to ensure this software freedom.  However, although the

definition of CCS is expansive, it is not sufficient to protect users'

freedoms in many circumstances.  For example, a GPL'd program, or a modified

version of such a program, might be locked-down and restricted.  The

requirements in GPLv3~\S6 (discussed in Section~\ref{GPLv3s6} of this

tutorial) handle that issue.  (Early drafts of GPLv3 included those

requirements in the definition of CCS; however, given that the lock-down

issue only comes up in distribution of object code, it is more logical to

place those requirements with the parts of GPLv3 dealing directly with object

code distribution).

The penultimate paragraph in GPLv3\S2 notes that GPLv3's CCS definition does

not require source that can be automatically generated.  Many code

generators, preprocessors and take source code as input and sometimes even

have output that is still source code.  Source code should always be whatever

the original programmer preferred to modify.

GPLv3\S1's final paragraph removes any ambiguity about what should be done on

source-only distributions.  Specifically, the right to convey source code

that does not compile, does not work, or otherwise is experimental

in-progress work is fully permitted, \textit{provided that} no object code

form is conveyed as well.  Indeed, when combined with the permissions in

GPLv3\S~5, it is clear that if one conveys \textit{only} source code, one can

never be required to provide more than that.  One always has the right to

modify a source code work by deleting any part of it, and there can be no

requirement that free software source code be a whole functioning program.

\subsection{The System Library Exception}

\label{GPLv3-system-library-exception}

The previous section skipped over one part of the CCS definition, the

so-called system library exception.  The ``System Libraries'' definition (and

the ``Standard Interface'' and ``Major Component'' definitions, which it

includes) are designed as part

to permit certain distribution arrangements that are considered reasonable by

copyleft advocates.  The system library exception is designed to allow

copylefted software to link with these libraries when prohibition of that linking would hurt

software freedom more than it would hurt proprietary software.

The system library exception has two parts.  Part (a) rewords the GPLv2

exception for clarity replacing GPLv2's words ``unless that component itself

accompanies the executable'' with ``which is not part of the Major

Component''.  The goal here is to not require disclosure of source code of

certain libraries, such as necessary Microsoft Windows DLLs (which aren't

part of Windows' kernel but accompany it) that are required for functioning

of copylefted programs compiled for Windows.

However, in isolation, (a) would be too permissive, as it would sometimes

allowing distributors to evade important GPL requirements.  Part (b) reigns

in (a).  Specifically, (b) specifies only a few functionalities that a

system library may provide and still qualify for the exception.  The goal is

to ensure system libraries are truly adjunct to a major essential operating

system component, compiler, or interpreter.  The more low-level the

functionality provided by the library, the more likely it is to be qualified

for this exception.

Admittedly, the system library exception is a frequently discussed topic of

obsessed GPL theorists.  The amount that has been written on the system

library exception (both the GPLv2 and GPLv3 versions of it), if included

herein,  could easily increase this section of the tutorial to a length

greater than all the others.

Like any exception to the copyleft requirements of GPL, would-be GPL

violators frequently look to the system library exception as a potential

software freedom circumvention technique.  When considering whether or not a

library qualifies for the system library exception, here is a pragmatic

thesis to consider, based on the combined decades of experience in GPL

interpretation of this tutorial's authors: the harder and more strained the

reader must study and read the system library exception, the more likely it

is that the library in question does not qualify for it.

\section{GPLv3~\S2: Basic Permissions}

\label{GPLv3S2}

GPLv3~\S2 can roughly be considered as an equivalent to GPLv2~\S0 (discussed

in \S~\ref{GPLv2s0} of this tutorial).  However, the usual style of

improvements found in GPLv3 are found here as well.  For example, the first

sentence of GPLv3~\S2 furthers the goal internationalization.  Under the

copyright laws of some countries, it may be necessary for a copyright license

to include an explicit provision setting forth the duration of the rights

being granted. In other countries, including the USA, such a provision is

unnecessary but permissible.

GPLv3~\S2\P1 also acknowledges that licensees under the GPL enjoy rights of

copyright fair use, or the equivalent under applicable law.  These rights are

compatible with, and not in conflict with, the freedoms that the GPL seeks to

protect, and the GPL cannot and should not restrict them.

However, note that (sadly to some copyleft advocates) the unlimited freedom

to run is confined to the \textit{unmodified} Program.  This confinement is

unfortunately necessary since Programs that do not qualify as a User Product

in GPLv3~\S6 (see \S~\ref{user-product} in this tutorial) might have certain

unfortunate restrictions on the freedom to run.\footnote{See

  \S~\ref{freedom-to-run} of this tutorial for the details on ``the freedom to

  run''.}

GPLv3~\S2\P2 distinguishes between activities of a licensee that are

permitted without limitation and activities that trigger additional

requirements.  Specifically, GPLv3~\S2\P2 guarantees the basic freedoms of

privately modifying and running the program.  While these basic freedoms were

generally considered a standard part of users' rights under GPLv2 as well,

the GPLv3 states them herein more explicitly.  In other words, there is no

direct analog to the first sentence of GPLv3~\S2\P2 in GPLv2

(See \S~\ref{gplv2-private-modification} of this tutorial for more on this issue.)

Also, GPLv3~\S2\P2 gives an explicit permission for a client to provide a

copy of its modified software to a contractor exclusively for that contractor

to modify it further, or run it, on behalf of the client.  However, the

client can \textit{only} exercise this control over its own copyrighted

changes to the GPL-covered program.  The parts of the program it obtained

from other contributors must be provided to the contractor with the usual GPL

freedoms.  Thus, GPLv3 permits users to convey covered works to contractors

operating exclusively on the users' behalf, under the users' direction and

control, and to require the contractors to keep the users' copyrighted

changes confidential, but \textit{only if} the contractor is limited to acting

on the users' behalf (just as the users' employees would have to act).

The strict conditions in this ``contractors provision'' are needed so that it

cannot be twisted to fit other activities, such as making a program available

to downstream users or customers.  By making the limits on this provision

very narrow, GPLv3 ensures that, in all other cases, contractor gets the

full freedoms of the GPL that they deserve.

The FSF was specifically asked to add this ``contractors provisions'' by

large enterprise users of Free Software, who often contract with non-employee