The Free Software Definition is set forth in full on the FSF's website at

\item The freedom to study how the program works, and to modify it.

\item The freedom to distribute copies of modified versions to others.

issue.  Though user access to the source code of a program is a

prerequisite to make use of the freedom to modify, the important

software, but this is quite common today. Most End User License Agreements

freely among members of the development community.\footnote{This is often

 still the case, though today there are additional ways of

Copyright is not a natural state; it is a legal construction. In the USA, the

% Potential re-write: 

% +-----------------+ 

Software, in a state of nature, is Free Software.

In an imaginary world without copyright, when you receive 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}.}

% Come back to this. The idea that software has a copyright-less natural 

% state contradicts copyright law as it exists, which assumes copyright 

% (as stated in the prev. paragraph.) Not even sure if my rewrite is correct.

Software in the real world is copyrighted by default and is automatically covered by 

such a 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 United States 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} 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 \emph{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~\ref{Free Software Definition} 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~\ref{non-usa-copyright} 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, which was supposed to only exist for ``Limited Times'' according to the 

United States 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 United States government.  Under 

\href{http://www.law.cornell.edu/uscode/text/17/105}{17 USC 101 \S~105}, all works 

published by the United States Government are not copyrightable in the USA.

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 \emph{is} copyrighted. In most cases (particularly in those of 

FSF and the GNU Project), this was done due to very careful planning.

Free Software released into the public domain is only guaranteed to be initially Free, and

perhaps some who modify the software might choose to place their work into the

proprietarize their modified versions. The public domain body of software then

extend'' cycle found in software released to the public domain, 

the FSF made a conscious choice to copyright its Free Software,

and to then license it under ``copyleft'' terms. Many, including the

modify, and improve creative works of authorship.  Copyleft (as a general

the copyright law's controls to ensure that all who receive a copy of the

not a dichotomy, it's a spectrum.  The strongest copylefts use the

exclusive rights that copyright  grants authors as extensively as possible

but reach other tactical goals for the community of users and developers of the

In other words, strong copyleft licenses place more requirements on how

  the license fits the \hyperref[Free Software Definition]{Free Software

earlier via footnotes, copyright is merely the \textit{most common way} to

  legally prohibits users from circumventing some of these DRM systems.

legal and technological means.  Any license that truly respects the software

but must also \textit{prevent} restrictions from other legal and technological

such as the right of an author to require proper attribution for their work.

introduced the idea of \textit{copyleft}: a licensing mechanism which uses

those rights against the actions of those who might seek to curtail them.

in this section, deeper discussion of how the GPL accomplishes this in practice

    ``A bit of history and a bit of fun''.}}  However, very

that because of the nature of the GPL, improvements that were

Samba, so noncommercial users, and even other commercial users, are