vs CC BY-SA 4.0

[Bradley M. Kuhn]

Winston de Greef wrote:
> I was wondering why I might consider this license instead of something like
> CC Attribution-ShareAlike 4.0 International.

The key reason that I recommend avoiding CC-BY-SA-4.0 is that it is *not* a
true copyleft.  Specifically, CC-BY-SA-4.0 (and other CC “share alike”s makes
basically no effort to assure that downstream recipients can *effectively*
take advantage of their right to modify.

Traditionally, software-focused copylefts always included some specific
description of what materials and rights must be provided downstream to allow
users/consumers to make *effective* use of their rights.  For example, GPLv2
talks about “complete, corresponding source code” which includes “scripts
used to control compilation and installation of the executable”.  A different
copyleft license, GPLv3, also has a lengthy definition for its defined term
“Corresponding Source”.

IMO, this material is the heart of what it means to be copyleft: if you can't
use the license to demand the artifacts you need *easily* engage in your
right to modify and/or install the software, then you don't really have a
copyleft license.

CC-BY-SA (any version) has never any real equivalent of a “source code
provision”.  The argument CC always made about this was that it's too hard to
define what “source code” is for works other than software (e.g., movies).

*But* there are some quite obvious activities that CC-BY-SA seems to allow
which are clearly not make it non-copyleft.  For example, CC-BY-SA [0] allows
licensees to take a CC-BY-SA'd high-quality SVG, turn it into a tiny PNG,
incorporate it into another work, but not provide the original SVG to
downstream.  In fact, they can do all their development in SVG and only
distribute the PNGs.

This is an obvious case where, if you're doing graphics editing as vector
images, the “corresponding source code” is clearly the SVG files you edited
in, say, Inkscape, not some PNG you exported at the end.

While copyleft-next is primarily going to be a software license, we
are actively thinking about this issues.

[0] To my knowledge, I'm not as expert in CC-BY-SA so if I'm mistaken, I
    welcome correction from others.


    -- bkuhn (he/them)