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| to ensure the perpetual availability to the public of a certain piece of information and all its derivative works. | to ensure the perpetual availability to the public of a certain piece of information and all its derivative works. | ||
| Initially only designed for ] distribution, the concept is now also being used for other types of material. | Initially only designed for ] distribution, the concept is now also being used for other types of material. | ||
| In copyleft, the copyright holder grants an irrevocable ] to the recipient of a copy, permitting the redistribution (including sale) of possibly modified further copies, under the condition that all those | In copyleft, the copyright holder grants an irrevocable ] to the recipient of a copy, permitting the redistribution (including sale) of possibly modified further copies, under the condition that all those | ||
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| The concept of copyleft arose | The concept of copyleft arose | ||
| when Stallman was working on a ] interpreter. ] asked to | when Stallman was working on a ] interpreter. ] asked to | ||
| use the |
use the LISP interpreter, and Stallman agreed to supply them with a | ||
| public domain version of his work. Symbolics extended and improved | public domain version of his work. Symbolics extended and improved | ||
| the |
the LISP interpreter, but when Stallman wanted access to the improvements | ||
| that Symbolics had made to his interpreter, Symbolics refused. Stallman | that Symbolics had made to his interpreter, Symbolics refused. Stallman | ||
| then proceeded to create a software license that would prevent this behavior. | then proceeded to create a software license that would prevent this behavior. | ||
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| The term "Copyleft" comes from the phrase "Copyleft--all rights reversed", which ] wrote in a message to Stallman in 1984 and which is intended as a double pun on the phrase "Copyright--all rights reserved". | The term "Copyleft" comes from the phrase "Copyleft--all rights reversed", which ] wrote in a message to Stallman in 1984 and which is intended as a double pun on the phrase "Copyright--all rights reserved". | ||
| ] which are examples of copyleft licenses include the ], the ], the ], and the ]. | ] which are examples of copyleft licenses include the ], the ], the ], and the ]. | ||
| Copyleft licenses for publications include the ], and the ]. The latter is being used for the contents of this ]. | Copyleft licenses for publications include the ], and the ]. The latter is being used for the contents of this ]. | ||
Revision as of 01:54, 29 May 2002
Copyleft refers to a concept invented by Richard Stallman of the Free Software Foundation in 1984: the application of copyright laws to ensure the perpetual availability to the public of a certain piece of information and all its derivative works. Initially only designed for software distribution, the concept is now also being used for other types of material.
In copyleft, the copyright holder grants an irrevocable license to the recipient of a copy, permitting the redistribution (including sale) of possibly modified further copies, under the condition that all those
copies carry the same license and are made available in a form which facilitates modification.
Some other open source licenses, such as those used by BSD and the X Window System, are not copyleft licenses because they do not extend to derivative works and include no requirement to make source code available. It is a matter of debate whether these licenses (and public domain material) provide a larger or smaller degree of freedom than copyleft licenses. While the former licenses attempt to maximize the freedom of the initial recipient, the latter licenses try to maximize the freedom of all potential recipients in the future.
Copyleft is sometimes (often by opponents) referred to as a virus or a viral license because any works based on a copylefted work must themselves be copylefted. Advocates of copyleft point out that most proprietary licenses prohibit creating derivative works altogether.
The concept of copyleft arose when Stallman was working on a LISP interpreter. Symbolics asked to use the LISP interpreter, and Stallman agreed to supply them with a public domain version of his work. Symbolics extended and improved the LISP interpreter, but when Stallman wanted access to the improvements that Symbolics had made to his interpreter, Symbolics refused. Stallman then proceeded to create a software license that would prevent this behavior.
The term "Copyleft" comes from the phrase "Copyleft--all rights reversed", which Don Hopkins wrote in a message to Stallman in 1984 and which is intended as a double pun on the phrase "Copyright--all rights reserved".
Free software licenses which are examples of copyleft licenses include the GNU General Public License, the GNU Lesser General Public License, the Mozilla Public License, and the Qt Public License. Copyleft licenses for publications include the Open Content License, and the GNU Free Documentation License. The latter is being used for the contents of this encyclopedia.