The BSD License Problem

The two major categories of free software license are copyleft [ http://www.gnu.org/copyleft/copyleft.html ] and non-copyleft [ http://www.gnu.org/philosophy/categories.html#Non-CopyleftedFreeSoftware ] . Copyleft licenses such as the GNU GPL [ http://www.gnu.org/copyleft/gpl.html ] insist that modified versions of the program must be free software as well. Non-copyleft licenses do not insist on this. We recommend copyleft, because it protects freedom for all users, but non-copylefted software is nonetheless useful to the free software community.

There are many different non-copyleft free software licenses, including the X10 license, the XFree86 license, and the FreeBSD license, and the BSD (Berkeley System Distribution) license.

Most of these non-copyleft licenses are equivalent except for details of wording, but the BSD license has a special problem: the ``obnoxious BSD advertising clause'', which leads to a kind of gridlock for advertising free software. The clause says that every advertisement mentioning the software must include a particular sentence:

3. All advertising materials mentioning features or use of this software
   must display the following acknowledgement:
     This product includes software developed by the University of
     California, Berkeley and its contributors.

If the obnoxious BSD advertising clause were used only in the Berkeley System Distribution, then it would not cause a major problem. Including one sentence in an ad is not a great practical difficulty. If other developers who use BSD-style licenses copied the BSD advertising clause verbatim--including the sentence that refers to the University of California--then they would not make the problem any bigger.

But that isn't what people do. Typically they change the required sentence, replacing ``University of California'' with their own institution or their own names. The result is a plethora of programs requiring a plethora of different sentences.

When people put many such programs together in an operating system, the result is a serious problem. Imagine if a software system required 75 different sentences, each one naming a different author or group of authors. You could not advertise that with less than a full-page ad.

This might seem like extrapolation ad absurdum, but it is simple fact. NetBSD comes with a long list of different sentences required for any advertisement; I counted 75 of them. That was in a manual I saw in 1997. I would not be surprised if the list has grown by now.

To address this problem, in my spare time I talk with developers who have used BSD-style licenses, asking them to remove the advertising clause. A couple of years ago I spoke with the developers of FreeBSD about this, and they decided to stop using the advertising clause on their own code. In May 1998 the developers of Flick, at the University of Utah, removed this clause. I am now talking with the University of California; maybe, just maybe, they will remove the obnoxious BSD advertising clause from BSD itself.

Addressing individual instances of this problem will help to solve it, but not if it keeps spreading. This problem is specific to the BSD license; other non-copyleft licenses don't add to it. So if you want to release a program as non-copylefted free software, please don't use a BSD-style license. By using some other non-copyleft license, such as the one used by XFree86 now, you can avoid spreading the problem.

When people refer to all non-copyleft free software licenses as ``BSD licenses'', that can lead new free software developers to spread this problem without even thinking about it. To encourage awareness of the issue, please don't describe a license ``BSD-style'' unless you mean specifically the BSD license with its troublesome advertising clause.

If you would like to cite one specific example of a non-copyleft licenses, and you have no particular preference, please pick an example which has no particular problem. For instance, if you suggest using an ``XFree86-style license'', you will encourage people to imitate XFree86 rather than BSD.

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