The following was contributed by anonymous trolls in 2004. It is rather amazing that it was not ported into this wiki from its predecessor rather than continuing to be enhanced. An exact definition of this concept is one of the foundations of CC itself.
The CC concept of Share Alike means strictly and only "share with (some) others on the same terms they have shared with you". It does not require that this sharing be with "everyone" as in "copyleft". Though that is an option (the CC-by-sa for instance) in the CC parametric license regime it is not a universal: the CC-by-nc-sa for instance does not share with commercial parties. In this sense it is like a sort of nonprofit consortium license.
Its general concept of sharing might include for instance a:
- shareware license where all who have paid a certain license fee might have the right to source code, but all others not.
- science license where all who have followed the scientific method may be able to make derivative works, but others would be subject to a NoDerivs restriction, as their derivative works would not advance science.
- CC-by-sa-fd which would enable sharing of GFDL corpus into the Common Content base. Note: CC-wiki does this to some degree.
not all Common Content is SA
Share Alike is orthogonal to Common Content as the latter includes both SA and non-SA terms on that content.
open content, free software are SA
- open content requires more careful specific attribution
- Free Software requires sharing with literally everyone
Accordingly it is possible to bring both of these ultimately into the parametric license regime both as SA licenses.
open source is not SA
Open source requires sharing with literally everyone but does not require them to share back with you - they can make their own proprietary extensions and enhancements and can withhold them. Accordingly open source is simply not SA but is more like the CC-by - though open source does not in many cases guarantee credit or any means of creator validation. It is a simple gift to everyone that can be used against its creator, or against its creator's values.