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GNU Home / Philosophy / Essays & articles / About free software /
Principles /
What is Free Software?
"Free software" means software that respects users' freedom and
community. Roughly, it means that the users have the freedom to run,
copy, distribute, study, change and improve the software. Thus, "free
software" is a matter of liberty, not price. To understand the concept,
you should think of "free" as in "free speech," not as in "free beer."
We sometimes call it "libre software," borrowing the French or Spanish
word for "free" as in freedom, to show we do not mean the software is
gratis.
You may have paid money to get copies of a free program, or you may
have obtained copies at no charge. But regardless of how you got your
copies, you always have the freedom to copy and change the software,
even to sell copies.
We campaign for these freedoms because everyone deserves them. With
these freedoms, the users (both individually and collectively) control
the program and what it does for them. When users don't control the
program, we call it a "nonfree" or "proprietary" program. The nonfree
program controls the users, and the developer controls the program;
this makes the program an instrument of unjust power.
"Open source" is something different: it has a very different
philosophy based on different values. Its practical definition is
different too, but nearly all open source programs are in fact free. We
explain the difference in Why "Open Source" misses the point of Free
Software.
__________________________________________________________________
Table of contents
* The Free Software Definition
+ The four essential freedoms
+ Free software can be commercial
* Clarifying the Boundary Between Free and Nonfree
+ The freedom to run the program as you wish
+ The freedom to study the source code and make changes
+ The freedom to redistribute if you wish: basic requirements
+ Copyleft
+ Rules about packaging and distribution details
+ Export regulations
+ Legal considerations
+ Contract-based licenses
* The Free Software Definition in Practice
+ How we interpret these criteria
+ Get help with free licenses
+ Use the right words when talking about free software
* Beyond Software
* History
Have a question about free software licensing not answered here? See
our other licensing resources, and if necessary contact the FSF
Compliance Lab at licensing@fsf.org.
__________________________________________________________________
The Free Software Definition
The free software definition presents the criteria for whether a
particular software program qualifies as free software. From time to
time we revise this definition, to clarify it or to resolve questions
about subtle issues. See the History section below for a list of
changes that affect the definition of free software.
The four essential freedoms
A program is free software if the program's users have the four
essential freedoms: [1]
* The freedom to run the program as you wish, for any purpose
(freedom 0).
* The freedom to study how the program works, and change it so it
does your computing as you wish (freedom 1). Access to the source
code is a precondition for this.
* The freedom to redistribute copies so you can help others (freedom
2).
* The freedom to distribute copies of your modified versions to
others (freedom 3). By doing this you can give the whole community
a chance to benefit from your changes. Access to the source code is
a precondition for this.
A program is free software if it gives users adequately all of these
freedoms. Otherwise, it is nonfree. While we can distinguish various
nonfree distribution schemes in terms of how far they fall short of
being free, we consider them all equally unethical.
In any given scenario, these freedoms must apply to whatever code we
plan to make use of, or lead others to make use of. For instance,
consider a program A which automatically launches a program B to handle
some cases. If we plan to distribute A as it stands, that implies users
will need B, so we need to judge whether both A and B are free.
However, if we plan to modify A so that it doesn't use B, only A needs
to be free; B is not pertinent to that plan.
Free software can be commercial
"Free software" does not mean "noncommercial." On the contrary, a free
program must be available for commercial use, commercial development,
and commercial distribution. This policy is of fundamental
importance--without this, free software could not achieve its aims.
We want to invite everyone to use the GNU system, including businesses
and their workers. That requires allowing commercial use. We hope that
free replacement programs will supplant comparable proprietary
programs, but they can't do that if businesses are forbidden to use
them. We want commercial products that contain software to include the
GNU system, and that would constitute commercial distribution for a
price. Commercial development of free software is no longer unusual;
such free commercial software is very important. Paid, professional
support for free software fills an important need.
Thus, to exclude commercial use, commercial development or commercial
distribution would hobble the free software community and obstruct its
path to success. We must conclude that a program licensed with such
restrictions does not qualify as free software.
A free program must offer the four freedoms to any would-be user that
obtains a copy of the software, who has complied thus far with the
conditions of the free license covering the software in any previous
distribution of it. Putting some of the freedoms off limits to some
users, or requiring that users pay, in money or in kind, to exercise
them, is tantamount to not granting the freedoms in question, and thus
renders the program nonfree.
Clarifying the Boundary Between Free and Nonfree
In the rest of this article we explain more precisely how far the
various freedoms need to extend, on various issues, in order for a
program to be free.
The freedom to run the program as you wish
The freedom to run the program means the freedom for any kind of person
or organization to use it on any kind of computer system, for any kind
of overall job and purpose, without being required to communicate about
it with the developer or any other specific entity. In this freedom, it
is the user's purpose that matters, not the developer's purpose; you as
a user are free to run the program for your purposes, and if you
distribute it to someone else, she is then free to run it for her
purposes, but you are not entitled to impose your purposes on her.
The freedom to run the program as you wish means that you are not
forbidden or stopped from making it run. This has nothing to do with
what functionality the program has, whether it is technically capable
of functioning in any given environment, or whether it is useful for
any particular computing activity.
For example, if the code arbitrarily rejects certain meaningful
inputs--or even fails unconditionally--that may make the program less
useful, perhaps even totally useless, but it does not deny users the
freedom to run the program, so it does not conflict with freedom 0. If
the program is free, the users can overcome the loss of usefulness,
because freedoms 1 and 3 permit users and communities to make and
distribute modified versions without the arbitrary nuisance code.
"As you wish" includes, optionally, "not at all" if that is what you
wish. So there is no need for a separate "freedom not to run a
program."
The freedom to study the source code and make changes
In order for freedoms 1 and 3 (the freedom to make changes and the
freedom to publish the changed versions) to be meaningful, you need to
have access to the source code of the program. Therefore, accessibility
of source code is a necessary condition for free software. Obfuscated
"source code" is not real source code and does not count as source
code.
Source code is defined as the preferred form of the program for making
changes in. Thus, whatever form a developer changes to develop the
program is the source code of that developer's version.
Freedom 1 includes the freedom to use your changed version in place of
the original. If the program is delivered in a product designed to run
someone else's modified versions but refuse to run yours--a practice
known as "tivoization" or "lockdown," or (in its practitioners'
perverse terminology) as "secure boot"--freedom 1 becomes an empty
pretense rather than a practical reality. These binaries are not free
software even if the source code they are compiled from is free.
One important way to modify a program is by merging in available free
subroutines and modules. If the program's license says that you cannot
merge in a suitably licensed existing module--for instance, if it
requires you to be the copyright holder of any code you add--then the
license is too restrictive to qualify as free.
Whether a change constitutes an improvement is a subjective matter. If
your right to modify a program is limited, in substance, to changes
that someone else considers an improvement, that program is not free.
One special case of freedom 1 is to delete the program's code so it
returns after doing nothing, or make it invoke some other program.
Thus, freedom 1 includes the "freedom to delete the program."
The freedom to redistribute if you wish: basic requirements
Freedom to distribute (freedoms 2 and 3) means you are free to
redistribute copies, either with or without modifications, either
gratis or charging a fee for distribution, to anyone anywhere. Being
free to do these things means (among other things) that you do not have
to ask or pay for permission to do so.
You should also have the freedom to make modifications and use them
privately in your own work or play, without even mentioning that they
exist. If you do publish your changes, you should not be required to
notify anyone in particular, or in any particular way.
Freedom 3 includes the freedom to release your modified versions as
free software. A free license may also permit other ways of releasing
them; in other words, it does not have to be a copyleft license.
However, a license that requires modified versions to be nonfree does
not qualify as a free license.
The freedom to redistribute copies must include binary or executable
forms of the program, as well as source code, for both modified and
unmodified versions. (Distributing programs in runnable form is
necessary for conveniently installable free operating systems.) It is
OK if there is no way to produce a binary or executable form for a
certain program (since some languages don't support that feature), but
you must have the freedom to redistribute such forms should you find or
develop a way to make them.
Copyleft
Certain kinds of rules about the manner of distributing free software
are acceptable, when they don't conflict with the central freedoms. For
example, copyleft (very simply stated) is the rule that when
redistributing the program, you cannot add restrictions to deny other
people the central freedoms. This rule does not conflict with the
central freedoms; rather it protects them.
In the GNU project, we use copyleft to protect the four freedoms
legally for everyone. We believe there are important reasons why it is
better to use copyleft. However, noncopylefted free software is ethical
too. See Categories of Free Software for a description of how "free
software," "copylefted software" and other categories of software
relate to each other.
Rules about packaging and distribution details
Rules about how to package a modified version are acceptable, if they
don't substantively limit your freedom to release modified versions, or
your freedom to make and use modified versions privately. Thus, it is
acceptable for the license to require that you change the name of the
modified version, remove a logo, or identify your modifications as
yours. As long as these requirements are not so burdensome that they
effectively hamper you from releasing your changes, they are
acceptable; you're already making other changes to the program, so you
won't have trouble making a few more.
Rules that "if you make your version available in this way, you must
make it available in that way also" can be acceptable too, on the same
condition. An example of such an acceptable rule is one saying that if
you have distributed a modified version and a previous developer asks
for a copy of it, you must send one. (Note that such a rule still
leaves you the choice of whether to distribute your version at all.)
Rules that require release of source code to the users for versions
that you put into public use are also acceptable.
A special issue arises when a license requires changing the name by
which the program will be invoked from other programs. That effectively
hampers you from releasing your changed version so that it can replace
the original when invoked by those other programs. This sort of
requirement is acceptable only if there's a suitable aliasing facility
that allows you to specify the original program's name as an alias for
the modified version.
Export regulations
Sometimes government export control regulations and trade sanctions can
constrain your freedom to distribute copies of programs
internationally. Software developers do not have the power to eliminate
or override these restrictions, but what they can and must do is refuse
to impose them as conditions of use of the program. In this way, the
restrictions will not affect activities and people outside the
jurisdictions of these governments. Thus, free software licenses must
not require obedience to any nontrivial export regulations as a
condition of exercising any of the essential freedoms.
Merely mentioning the existence of export regulations, without making
them a condition of the license itself, is acceptable since it does not
restrict users. If an export regulation is actually trivial for free
software, then requiring it as a condition is not an actual problem;
however, it is a potential problem, since a later change in export law
could make the requirement nontrivial and thus render the software
nonfree.
Legal considerations
In order for these freedoms to be real, they must be permanent and
irrevocable as long as you do nothing wrong; if the developer of the
software has the power to revoke the license, or retroactively add
restrictions to its terms, without your doing anything wrong to give
cause, the software is not free.
A free license may not require compliance with the license of a nonfree
program. Thus, for instance, if a license requires you to comply with
the licenses of "all the programs you use," in the case of a user that
runs nonfree programs this would require compliance with the licenses
of those nonfree programs; that makes the license nonfree.
It is acceptable for a free license to specify which jurisdiction's law
applies, or where litigation must be done, or both.
Contract-based licenses
Most free software licenses are based on copyright, and there are
limits on what kinds of requirements can be imposed through copyright.
If a copyright-based license respects freedom in the ways described
above, it is unlikely to have some other sort of problem that we never
anticipated (though this does happen occasionally). However, some free
software licenses are based on contracts, and contracts can impose a
much larger range of possible restrictions. That means there are many
possible ways such a license could be unacceptably restrictive and
nonfree.
We can't possibly list all the ways that might happen. If a
contract-based license restricts the user in an unusual way that
copyright-based licenses cannot, and which isn't mentioned here as
legitimate, we will have to think about it, and we will probably
conclude it is nonfree.
The Free Software Definition in Practice
How we interpret these criteria
Note that criteria such as those stated in this free software
definition require careful thought for their interpretation. To decide
whether a specific software license qualifies as a free software
license, we judge it based on these criteria to determine whether it
fits their spirit as well as the precise words. If a license includes
unconscionable restrictions, we reject it, even if we did not
anticipate the issue in these criteria. Sometimes a license requirement
raises an issue that calls for extensive thought, including discussions
with a lawyer, before we can decide if the requirement is acceptable.
When we reach a conclusion about a new issue, we often update these
criteria to make it easier to see why certain licenses do or don't
qualify.
Get help with free licenses
If you are interested in whether a specific license qualifies as a free
software license, see our list of licenses. If the license you are
concerned with is not listed there, you can ask us about it by sending
us email at <licensing@gnu.org>.
If you are contemplating writing a new license, please contact the Free
Software Foundation first by writing to that address. The proliferation
of different free software licenses means increased work for users in
understanding the licenses; we may be able to help you find an existing
free software license that meets your needs.
If that isn't possible, if you really need a new license, with our help
you can ensure that the license really is a free software license and
avoid various practical problems.
Use the right words when talking about free software
When talking about free software, it is best to avoid using terms like
"give away" or "for free," because those terms imply that the issue is
about price, not freedom. Some common terms such as "piracy" embody
opinions we hope you won't endorse. See Confusing Words and Phrases
that are Worth Avoiding for a discussion of these terms. We also have a
list of proper translations of "free software" into various languages.
Another group uses the term "open source" to mean something close (but
not identical) to "free software." We prefer the term "free software"
because, once you have heard that it refers to freedom rather than
price, it calls to mind freedom. The word "open" never refers to
freedom.
Beyond Software
Software manuals must be free, for the same reasons that software must
be free, and because the manuals are in effect part of the software.
The same arguments also make sense for other kinds of works of
practical use--that is to say, works that embody useful knowledge, such
as educational works and reference works. Wikipedia is the best-known
example.
Any kind of work can be free, and the definition of free software has
been extended to a definition of free cultural works applicable to any
kind of works.
History
From time to time we revise this Free Software Definition. Here is the
list of substantive changes, along with links to show exactly what was
changed.
* Version 1.169: Explain more clearly why the four freedoms must
apply to commercial activity. Explain why the four freedoms imply
the freedom not to run the program and the freedom to delete it, so
there is no need to state those as separate requirements.
* Version 1.165: Clarify that arbitrary annoyances in the code do not
negate freedom 0, and that freedoms 1 and 3 enable users to remove
them.
* Version 1.153: Clarify that freedom to run the program means
nothing stops you from making it run.
* Version 1.141: Clarify which code needs to be free.
* Version 1.135: Say each time that freedom 0 is the freedom to run
the program as you wish.
* Version 1.134: Freedom 0 is not a matter of the program's
functionality.
* Version 1.131: A free license may not require compliance with a
nonfree license of another program.
* Version 1.129: State explicitly that choice of law and choice of
forum specifications are allowed. (This was always our policy.)
* Version 1.122: An export control requirement is a real problem if
the requirement is nontrivial; otherwise it is only a potential
problem.
* Version 1.118: Clarification: the issue is limits on your right to
modify, not on what modifications you have made. And modifications
are not limited to "improvements"
* Version 1.111: Clarify 1.77 by saying that only retroactive
restrictions are unacceptable. The copyright holders can always
grant additional permission for use of the work by releasing the
work in another way in parallel.
* Version 1.105: Reflect, in the brief statement of freedom 1, the
point (already stated in version 1.80) that it includes really
using your modified version for your computing.
* Version 1.92: Clarify that obfuscated code does not qualify as
source code.
* Version 1.90: Clarify that freedom 3 means the right to distribute
copies of your own modified or improved version, not a right to
participate in someone else's development project.
* Version 1.89: Freedom 3 includes the right to release modified
versions as free software.
* Version 1.80: Freedom 1 must be practical, not just theoretical;
i.e., no tivoization.
* Version 1.77: Clarify that all retroactive changes to the license
are unacceptable, even if it's not described as a complete
replacement.
* Version 1.74: Four clarifications of points not explicit enough, or
stated in some places but not reflected everywhere:
+ "Improvements" does not mean the license can substantively
limit what kinds of modified versions you can release. Freedom
3 includes distributing modified versions, not just changes.
+ The right to merge in existing modules refers to those that
are suitably licensed.
+ Explicitly state the conclusion of the point about export
controls.
+ Imposing a license change constitutes revoking the old
license.
* Version 1.57: Add "Beyond Software" section.
* Version 1.46: Clarify whose purpose is significant in the freedom
to run the program for any purpose.
* Version 1.41: Clarify wording about contract-based licenses.
* Version 1.40: Explain that a free license must allow to you use
other available free software to create your modifications.
* Version 1.39: Note that it is acceptable for a license to require
you to provide source for versions of the software you put into
public use.
* Version 1.31: Note that it is acceptable for a license to require
you to identify yourself as the author of modifications. Other
minor clarifications throughout the text.
* Version 1.23: Address potential problems related to contract-based
licenses.
* Version 1.16: Explain why distribution of binaries is important.
* Version 1.11: Note that a free license may require you to send a
copy of versions you distribute to previous developers on request.
There are gaps in the version numbers shown above because there are
other changes in this page that do not affect the definition or its
interpretations. For instance, the list does not include changes in
asides, formatting, spelling, punctuation, or other parts of the page.
You can review the complete list of changes to the page through the
cvsweb interface.
Footnote
1. The reason they are numbered 0, 1, 2 and 3 is historical. Around
1990 there were three freedoms, numbered 1, 2 and 3. Then we
realized that the freedom to run the program needed to be mentioned
explicitly. It was clearly more basic than the other three, so it
properly should precede them. Rather than renumber the others, we
made it freedom 0.
__________________________________________________________________
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