GPL with the Classpath exception - clarification needed

John Cowan cowan at
Wed Mar 25 07:08:07 UTC 2009

Blake White scripsit:

> But the Classpath library says that "If you modify this library,
> you may extend this exception to your version of the library, but you
> are not obligated to do so."
> So by that line, if I'm a third party and I modify the library,
> can't I extend the exception to my modified library, effectively making
> "this library" now mean the modified version?

Yes, you can, and that helps your downstream users -- but it does not
help you.  The GPL still forbids you to distribute proprietary software
with your modified library in it.

You could in theory escape this by collusion.  Bob could take Alice's
GPL+CP library, modify it, and pass it under GPL+CP to Charlie -- who
makes a deal with Bob to take Bob's proprietary software and distribute
it it under his own name but for Bob's benefit.  Judges, however, look
with great disapproval on such scams -- they will interpret the terms
according to Alice's intentions.

John Cowan       cowan at
                if if = then then then = else else else = if;

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