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[Savannah-hackers-public] Needing clarifications regarding compatibility
[Savannah-hackers-public] Needing clarifications regarding compatibility between the GPL and FreeType Project License
Tue, 08 Feb 2005 22:28:36 +0100
Mozilla Thunderbird 1.0 (Windows/20041206)
I'm the main author of the open-source FreeType font libraries, which is
released under both its own BSD-like license (called the FreeType Project
and the GPL. Note that the FTL can be retrieved from the following web page:
The reason for the dual licensing is historical:
* we initially released our code under the FTL only (a long time ago)
* some users told us that our license was not compatible with the GPL
due to our "advertising clause"
* as a consequence, we contacted Richard Stallman, which confirmed us
by email that, indeed, the two licenses were incompatible.
* we promptly decided to dual-release our code.
I must say that this move hasn't been very well understood by everyone,
we still receive regularly requests from users who do not understand the
dual icensing's purpose, though we try to explain it clearly on our
web pages and documentation.
However, in light of our recent migration to the Savannah servers, one of
admins had a look at the license, and informed us that he couldn't see
why the licenses were incompatible. We then started investigating the
topic ourselves, by carefully reading any information you're providing
regarding GPL compatible and incompatible licenses on the GNU web sites.
Our final conclusion is that, indeed, the FTL and GPL are compatible,
for reasons that I'll try to explain in more details below. We would
appreciate if you could give a second look to the license and confirm
what we've found, or enlighten us for any non-trivial incompatibility
that we could not really spot.
My belief is that the license was incorrectly judged incompatible because
it includes a clause related to advertising that can mistaken for the infamous
"advertising clause" of the original BSD license (which is not compatible).
However, our own clause is quite different, and clearly unrestrictive.
Your opinion on the subject would be deeply appreciated. We would like
to stop the dual-licensing and make it very clear that it is not needed
anymore (and never was in the first place)
- David Turner
- The FreeType Project
PS: An overview of the FTL, with comparison to the GPL:
The following refers to sections of the license available
at the following address:
this clause is used to define the scope of the license.
nothing unusual here.
FTL.1: No Warranty
this clause is a no-warranty disclaimer. It doesnt provide
permissions or restrictions.
this is made of two sub-clauses that are un-numbered in the
FTL.2.a: source re-distribution:
we believe this clause to be compatible with the GPL.
More specifically, clauses GPL.1 and GPL.2.a correspond
to the conditions described here
FTL.2.b: binary re-distribution:
we believe this clause compatible with the GPL.
More specifically, we believe that clauses GPL.2.b,
GPL.3.a correspond to the conditions described here
note that our binary redistribution clause is even
less restrictive than the one in the modified BSD
license, since we don't even ask for a complete
copy of the list of conditions in the product's
this clause is probably the reason for the initial confusion,
in our opinion. However, it is not worded as the original BSD
advertising clause. Indeed, it reads:
We suggest, but do not require, that you use one or more of the
following phrases to refer to this software in your documentation
or advertising materials: `FreeType Project', `FreeType Engine',
`FreeType library', or `FreeType Distribution'.
in other words, there is no advertising requirement associated
to this license.
well, no permissions or restrictions there as well, just some
Finally, notice that there exist several versions of the FTL. These
differ only in cosmetic attributes (e.g. typos); all versions correspond
to exactly the same set of permissions and restrictions, and should thus
be judged compatible as well (that is, unless you could prove us otherwise)
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