A license doesn't "relax" rights, it grants rights to others (and sometimes/in some jurisdictions also can limit how the copyright owner can make use of his rights)
If you give someone the right to do something and don't specify how you can take it away, you can't take it away again. Without termination clauses a license is a contract thats valid indefinitely.
And why can't you take it away? If I give someone a permit to cross my bridge, I can revoke it at any time. Usually when something is perpetual, you have to write in it: "perpetual" for it to actually be so.
Let's keep it with software. The bridge metaphor is more applicable to a service offering where you maintain infrastructure and adjust pricing based on the cost of maintaining it.
In software, the license is what you sell. I don't buy MS Windows or Photoshop, I buy a license for it. If you sell me a 3-seat license of software v1.0 allowing me to install it on up to 3 computers, you can't come back 2 years later and change the terms to only 1 computer. Now, in 2 years, you might have v2.0 and require a new license for that. But the license you sold me for v1.0 remains in place.
By releasing the software under the BSD license, he basically sold us a license (price immaterial) granting permission to redistribute and alter the code, provided that new code includes the BSD license.
I understand that wasn't his intention. Another commenter pointed out that the author gave permission to another project which was being released under the BSD license. Now anyone that was "sold" the software with that license has been granted those redistribution rights.
I did think of this, but surely a transaction between two parties is not the same as simply posting a license on a website?
If I pay money in return for a license to use Photoshop, there is a reasonable expectation that I can use that indefinitely. I give then money, they give me permission.
If I simply download a piece of open source software from the internet, that isn't the same thing. There's no transaction. There's no anything. If the author subsequently tells me "I hereby revoke all previous licenses", I don't see how that wouldn't have legal weight.
"If I pay money in return for a license to use Photoshop, there is a reasonable expectation that I can use that indefinitely. I give then money, they give me permission."
Money has nothing to do with it, all reproduction of bits is automatically covered by copyright law, and has a legal presumption of "all rights reserved" unless explicitly delineated in a license.
Even when paying money, it isn't a reasonable expectation to expect to be able to use it forever for all software. With shrink-wrap or click-through agreements, perhaps, by convention, but plenty of software is sold on subscription for example, or may have revocation clause without refund which is common with MMO games for example.
Some software also may naturally break some day due to incompatibility or disinterest by the author. Other than limited warranty protections by law, there's not much a buyer can do about it. This is of course subject to local laws which may allow moral revocation (France) or stricter warranties.
With regards to downloading a piece of open source, the downloader is consenting to the copyright license it is offered under: it's the same as a click through.
If there is no license, you technically have no right to use or redistribute the software (all rights are reserved).
If there is a license, usually that will explain the author's intentions for fees, redistribution rights, and rights of revocability.
The OSI exists to approve licenses as "open source" when they (among other clauses) explicitly denounce revocability. The only recourse is that an author can refuse to OSI license future modifications or releases of the software (basically making a private fork).
If you just tell someone you can use the bridge then you can probably revoke it. But if you keep letting them use it and they build a house on the other side of the bridge or something then you've probably granted an implied easement[1] and can't, in fact, suddenly stop letting them use the bridge. But in this case there's actually a legal document saying that anybody can use the bridge so that would be analogous to an express easement.
We are not talking about permits (which are typically temporary as per whatever conditions they have). We are talking about software licenses, which often do not allow the copyright holder to revoke.
These licenses are explicit about what they do/do not grant. p
If you give someone the right to do something and don't specify how you can take it away, you can't take it away again. Without termination clauses a license is a contract thats valid indefinitely.