| Revision as of 09:35, 2 April 2002 editAxelBoldt (talk | contribs)Administrators44,506 edits +viral license← Previous edit | Revision as of 09:42, 2 April 2002 edit undoAxelBoldt (talk | contribs)Administrators44,506 editsNo edit summaryNext edit → | ||
| Line 14: | Line 14: | ||
| This differs from some other ] licenses which allow proprietary works to be made from the software. | This differs from some other ] licenses which allow proprietary works to be made from the software. | ||
| Copyleft is sometimes referred to as a |
Copyleft is sometimes (often by opponents) referred to as a ] 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 simply prohibit creating derivative works. | Advocates of copyleft point out that most proprietary licenses simply prohibit creating derivative works. | ||
Revision as of 09:42, 2 April 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. 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.
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. This differs from some other open source licenses which allow proprietary works to be made from the software.
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 simply prohibit creating derivative works.
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 Q Public License. The simple permissive licenses of BSD and X Window System are not copyleft licenses because they do not restrict distribution of derivative works without source code. 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.