| Articles |
Copyright Issues
Open Source & Derivative Works
GPL Issues
GPL Validity
GPL Violations
WordPress & the GPL
Legal Cases
ProCD v. Zeidenberg
USL v. BSDi
| Glossary |
Advertising Clause
Click-Through License
Compatible Licenses
Copyleft
Derivative Works
Dual Licensing
EULA
FLOSS
FOSS
Free Software
Incompatible Licenses
OSD
OSI Certified
OSS
Permissive Licenses
Shrink Wrap License
Viral Licenses
| Open Source |
Licenses
AGPL
Apache
Apple
Artistic
BSD
CDDL
CPL
EPL
GPL v2
GPL v3
IPL
LGPL
MIT
Mozilla
SPL
X License
X11 License
Organizations
ASF
FSF
OSI
SFLC
People
Bruce Perens
Eben Moglen
Eric Raymond
Lawrence Lessig
Linus Torvalds
Richard Stallman
| Proprietary Licenses |
Licenses
Closed Source
Freeware
Shareware
Organizations
BSA
| Shared Source Licenses |
MS Community License
MS Permissive License
| Uncopyrighted |
Public Domain
| Further Reading |
Books
| Software Licenses > Glossary > Copyleft |
Copyleft
Copyleft is a licensing system, were copyright law is used to enforce the removal of restrictions on distributing copies and modified versions of a work (including software works). In copyleft licenses such as the GPL, the owner of a copyright permits others to distribute their work (in either unmodified or modified form) but only provided the distributor (licensee) also allows others receiving the work to exercise the same freedoms. For this reason copyleft licenses are also sometimes known as "reciprocal licenses".
Copyleft licenses are also sometimes described to as "viral" on the basis that once a work is placed under a copyleft license, then additions to the work are also usually placed under the same copyleft license and so on. On the whole, the viral description tends to be frequently used by critics of copyleft licenses, whereas proponents generally point to the fact that derivative works can usually only be legally created with the copyright-holder's explicit permission for proprietary licensed software.
A symbol of a reversed letter c in a full circle (as opposed to a normal
letter c in a full circle) is sometimes used to indicate that a work is
copyleft, although unlike the copyright symbol, the copyleft symbol doesn't
have a particular legal meaning or effect.
Copyleft licenses are sometimes subdivided into subcategories based on various criteria:
- "Strong Copyleft" licenses
(example: GPL)
, are licenses where all
derivative works
must be distributed under a copyleft license, whereas
"Weak Copyleft" licenses
(example: LGPL)
only require some
derivative works
to be distributed under a copyleft license.
- "Full Copyleft" licenses cover an entire work, whereas "Partial Copyleft" licenses only cover particular parts of a work.
