www/licenses license-compatibility.html

[Richard M. Stallman]

CVSROOT:        /web/www
Module name:    www
Changes by:     Richard M. Stallman <rms>       20/11/20 11:15:07

Modified files:
        licenses       : license-compatibility.html 

Log message:
        Clarify points about version incompatibility.
        Correct statement about CC-BY-SA.
        Cite PHP example.

CVSWeb URLs:
http://web.cvs.savannah.gnu.org/viewcvs/www/licenses/license-compatibility.html?cvsroot=www&r1=1.9&r2=1.10

Patches:
Index: license-compatibility.html
===================================================================
RCS file: /web/www/www/licenses/license-compatibility.html,v
retrieving revision 1.9
retrieving revision 1.10
diff -u -b -r1.9 -r1.10
--- license-compatibility.html  15 Dec 2018 14:02:37 -0000      1.9
+++ license-compatibility.html  20 Nov 2020 16:15:06 -0000      1.10
@@ -77,17 +77,21 @@
 incompatible unless they have explicit compatibility provisions.  This
 is not due to a mistake in the details; it's inherent in the idea of
 copyleft.  The idea of copyleft is that &ldquo;Modified and extended
-versions must be under the same license.&rdquo;  If license A says extended
-programs must be under license A, and license B says extended programs
-must be under license B, they have an irreconcilable disagreement; the
-license of the combined program would have to be A, <em>and</em> it would
-have to be B.  This is why GPL version 2 is incompatible with GPL
-version 3; it could not be avoided.  Likewise, the conditions of
-CC-BY-SA 4.0 would be inherently incompatible with those of CC-BY-SA
-3.0, and the authors could not have avoided this.</p>
+versions must be under the same license.&rdquo; If license A (on
+program P) says extended programs must be under license A, and license
+B (on program Q) says extended programs must be under license B, they
+have an irreconcilable disagreement; the license of the combined
+program which includes code from P plus code from Q would have to be
+A, <em>and</em> it would have to be B.</p>
+
+<p>This is why GPL version 2 is
+incompatible with GPL version 3; it could not be avoided.  Likewise,
+the conditions of CC-BY-SA 4.0 would be inherently incompatible with
+those of CC-BY-SA 3.0, and the authors could not have avoided
+this.</p>
 
-<p>There are two approaches for smoothing out the incompatibility
-inherent in new versions of copyleft licenses.</p>
+<p>There are two approaches for avoiding the incompatibility problem
+caused by different versions of copyleft licenses.</p>
 
 <p>The FSF uses the approach of asking people to release programs under
 &ldquo;GNU GPL version N or any later version.&rdquo;  This licensing is
@@ -102,11 +106,11 @@
 releasing your code under GNU GPL 3 or later, you permit your code to
 upgrade to GNU GPL version 4 if we ever need one.</p>
 
-<p>The other approach is to make each version of the license explicitly
-allow upgrading to later versions.  This is what Creative Commons
-does: for instance, CC-BY-SA version 4.0 (the current version)
-explicitly permits any user to upgrade to later versions of CC-BY-SA
-once those exist.  The Mozilla Foundation also uses this approach.</p>
+<p>The other approach is to make each version of the license
+explicitly allow upgrading to later versions.  The Mozilla Foundation
+uses this approach, as does PHP.  Creative Commons, uses it for
+CC-BY-SA: version 4.0 (the current version) explicitly permits any
+user to upgrade to later versions of CC-BY-SA for modified works.</p>
 
 <p>Only the GNU licenses give authors a choice about whether to permit
 upgrades to future license versions.  When I wrote the first version
@@ -119,8 +123,9 @@
 <p>Since then, I have come to question the wisdom of that decision.
 Programs such as Linux, which allow only one GNU GPL version and
 reject license upgrades, cause practical
-incompatibility.<a href="#f4">(****)</a>  Perhaps we should include an
-upgrade clause in GPL version 4, if we ever need a version 4.</p>
+incompatibility.<a href="#f4">(****)</a>  If we ever make a GPL version
+4, perhaps we should include an upgrade clause that automatically
+permits relicensing to higher-numbered versions, 5 and up.</p>
 
 <p>Some copyleft licenses allow cross-copyleft combinations with an
 explicit relicensing clause giving permission to put the code under a
@@ -354,7 +359,7 @@
 
 <p class="unprintable">Updated:
 <!-- timestamp start -->
-$Date: 2018/12/15 14:02:37 $
+$Date: 2020/11/20 16:15:06 $
 <!-- timestamp end -->
 </p>
 </div>