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 \textbf{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.

\subsection{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.

\subsection{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

modification.

\subsection{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 of this freedom.  Commercial sharing

includes selling copies of Free Software: that is, Free Software can

be distribted 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~\ref{Business Models} of this tutorial talks in detail about some

common Free Software business models that take advantage of the freedom to

share commercially.)

\subsection{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

commonly the case, though today there are other or additional ways of

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

improvers 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.

\section{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 mechanism 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.

Proprietary software exists at all only because it is governed by copyright

law.\footnote{This 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.} Copyright law, with respect to

software, typically governs copying, modifying, and redistributing that

software (For details of this in the USA, see

\href{http://www.copyright.gov/title17/92chap1.html#106}{\S~106} and

\href{http://www.copyright.gov/title17/92chap1.html#117}{\S~117} of

\href{http://www.law.cornell.edu/uscode/text/17}{Title 17} of the

\textit{United States Code}).\footnote{Copyright 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.} 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 US, the

Constitution permits, but does not require, the creation of copyright law as

federal legislation.  Software, since it is ``an original works 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

\href{http://www.law.cornell.edu/uscode/text/17/102}{17 USC \S~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.\footnote{Note that this is again an oversimplification; the

  complexities with this argument are discussed in

  Section~\ref{software-and-non-copyright}.}

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

\defn{disclaim} their copyright (for example, under US 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.''

\subsection{Public Domain Software}

Theoretically, an author can create public domain software by disclaiming all