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From FreeBSD License:

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

1.Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

2.Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

I think this means the license should be reproduced on redistributions(with or without modifications) of original work but not on the entire derived work which makes it like a weak copyleft license. then why it is considered to be a permissive license?

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As I understand them, the two terms "copyleft license" and "permissive license" are not exclusive.

A "permissive license" is any license which permits use without specific individual permission from the user CC-By and CC-0 are permissive licenses, because they permit people to reuse the content without directly askign for permission. They also permit many other things as well. I would call even the CC-BY-NC-ND license permissive, although it forbids commercial use and the making or derivative works.

A copyleft license specifically requires reusers to grant to others permission on the same terms as they have been granted. The CC-BY-SA is a copyleft license in this sense. Many copyleft licenses also require that if a work under the license is incorporated into a larger work, the entire work must be distrusted under the same license. These are sometimes called "viral" licenses. The GPL is of this sort. Some people only use the term "copyleft" for this sort of license.

In any case, I think pretty much all copyleft licenses are also permissive, but not all permissive licenses are also copyleft. It might with some work be possible to create a copyleft license that was not permissive, but I don't know of any, and it would seem rather pointless.

However the Wikipedia article Permissive software license defines a "Permissive software license" as one that grants reuse rights, and also allows a user the right to re-license the work including placing it under a proprietary license, nd cites the BSD license. By this definition no copyleft license is permissive.

The FreeBSD or 2-clause BSD license requires that a copyright notice and the 2 condition's be included when a work is redistributed. It does not require that the work be distributed under the FreeBSD license, or a similar license.

The FreeBSD project has said that software releases under the FreeBSD license may be re-licensed under a proprietary license. "Why you should use a BSD style license for your Open Source Project - GPL Advantages and Disadvantages" by Bruce Montague includes the statement:

In contrast to the GPL, which is designed to prevent the proprietary commercialization of Open Source code, the BSD license places minimal restrictions on future behavior. This allows BSD code to remain Open Source or become integrated into commercial solutions, as a project's or company's needs change.

This is not a copyleft license at all.

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  • Thanks. so FreeBSD license allows re-licensing but target license must be compatible with FreeBSD (i.e. "retain the list of conditions") ?
    – pixo
    Dec 25 '21 at 18:25
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    @pixo as I understand it you must under the FreeBSD retain the copyright notice and the list of conditions, but you may freely add other restrictions, including one that prohibit further sharing. modification, or re-use, an "all rights reserved" license. I am not sure how any license would fail to be "compatible" with that. Dec 25 '21 at 18:30
  • so it's not necessary to retain "Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met" ?
    – pixo
    Dec 25 '21 at 18:42
  • because I think retaining that means further sharing and modification will be allowed.
    – pixo
    Dec 25 '21 at 18:43
  • @pixo Apparently not. That is not one of the following conditions. This seems to be by design Dec 25 '21 at 18:44
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OSI has a definition of 'permissive'

A "permissive" license is simply a non-copyleft open source license — one that guarantees the freedoms to use, modify, and redistribute, but that permits proprietary derivative works.

and a definition of 'copyleft'

"Copyleft" refers to licenses that allow derivative works but require them to use the same license as the original work.

This is agreed by the community.

The Free BSD License is essentially equivalent to the 2-clause BSD license (in some citations there is an additional disclaimer) and it is clearly permissive. The language "must retain the above copyright notice" does by no means imply that the distribution of code needs to be under the same license.

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  • Thanks. my question was mostly about "this list of conditions" in "must retain the above copyright notice, this list of conditions and the following disclaimer" not the copyright notice. David Siegel answer and comments clarified it for me. But I agree with you about definitions of permissive and copyleft licenses.
    – pixo
    Dec 26 '21 at 13:25
  • @pixo To be honest, how much can you trust in an answer of someone who started with... "As I understand them, the two terms "copyleft license" and "permissive license" are not exclusive." , as this is completely wrong. Your initial question indicated that you had doubts/questions about the nature and criteria of a permissive license. If you have specific questions about the list of conditions w.r.t. the BSD-2 license, then you can find a lot of answers on this site. Dec 26 '21 at 20:40
  • sorry I just saw your comment. You are right my question was indeed about the nature and criteria of a permissive license. More specifically I thought that the requirement of the license to retain the two conditions of the license on derived works violates the nature of permissive license and thus I must be wrong somewhere. I understand that marking currently accepted answer as accepted is not good for StackExchange in general. so if I see another answer that answers my main concern I will accept that one instead.
    – pixo
    Dec 29 '21 at 21:48

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