Study of the GNU General Public License (herein, abbreviated as \defn{GNU

  GPL} or just \defn{GPL}) must begin by first considering the broader world

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

(GPLv2 and GPLv3) and their terms and conditions is a basic understanding of

other software licenses in that they are designed to defend and uphold these

principles.

Software,\footnote{The political differences between the Free Software

  Movement and the Open Source Movement are documented on FSF's Web site at

  {\tt http://www.fsf.org/licensing/essays/free-software-for-freedom.html}.}

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 of that source code.

these freedoms for noncommercial activities but prohibit them for commercial

activities are considered non-free.  Even the Open Source Initiative

(\defn{OSI}) (the arbiter of what is considered ``Open Source'') also rules

In general, software for which most or all of these freedoms are

restricted in any way is called ``non-Free Software.''  Typically, the

Microsoft's and Oracle's offerings).

Keep in mind that the none of the terms ``software freedom'', ``open source''

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

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

``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

\subsection{The Freedom to Run}

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

(EULAs) that cover most proprietary software typically restrict some types of

uses.  Such restrictions of any kind are an unacceptable restriction on

software freedom.

install the binary applications from that source, users cannot effectively

exercise 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

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

among friends.

The commercial environment also benefits of this freedom.  Commercial sharing

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.

The freedom to modify and improve is somewhat empty without the freedom to

share those improvements.  The Software freedom community is built on the

sharing is the primary reason that Free Software thrives.

Commercial sharing of modified Free Software is equally important.

\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

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,

sense by distributing only binary code and keeping the source code of the

software secret.

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

However, software, in its natural state without copyright, is Free

Software. In an imaginary world with no copyright, the rules would be

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

``public domain.''

\subsection{Public Domain Software}