Perl is not BSD licensed. OpenBSD's worry is apparently section 6:

> 6. This License Agreement will automatically terminate upon a material breach of its terms and conditions.

which I'd have assumed implicit to pretty much every license — or at least every license with conditions — but I guess not if the PSF (or Mozilla which has a similar clause in the MPL) felt the need to specify it explicitly.

I wouldn’t assume so. Contracts often specify the opposite, that violation of one term does not void or negate the contract.

I don’t actually know, though. It just doesn’t seem like a safe assumption.

IANAL, but I have several in the family and have often been in a role to review contracts for professional services (I focus on the technical, legal focuses on the legal).

> I wouldn’t assume so. Contracts often specify the opposite, that violation of one term does not void or negate the contract.

I have not seen this language. Typically violating a condition of the contract means you are in breach. Sometimes remedies to certain breaches are enumerated in the contract.

The language about one item not voiding or negating the whole is often in regard to the legality of the contract, something like below (excerpted from an MSA from a client):

> If any term, condition, or provision in this Agreement is found to be invalid, unlawful, or unenforceable to any extent, the parties shall endeavor in good faith to agree to such amendments that will preserve, as far as possible, the intentions expressed in this Agreement. If the parties fail to agree on such an amendment, such invalid term, condition, or provision shall be severed from the remaining terms, conditions and provisions, which shall continue to be valid and enforceable to the fullest extent permitted by law.

This is basically saying if one term in the contract is voided, it does not void the whole contract. This is very different from "if you breach one term, the contract is not considered breached".

It might be related to the fact that both Python and Mozilla were, at one point, owned by actual companies. The wording might be specific to specific concepts of commercial law that are not particularly relevant elsewhere.

Practically speaking, there is no such thing as “BSD-incompatible license”. The only problem here is license proliferation.

Anything that significantly restricts use isn't something that you can distribute as part of a BSD licensed system. The restrictions on that piece would need to be met by anyone using or redistributing the system, which is a significant departure from expectations.

Certainly, you can use GPL software with a BSD licensed system, and you can distribute GPL packages to be installed on a BSD licensed system, but if you include GPL software in a BSD system, it's no longer a BSD system.

Indeed, but it’s not license compatibility - in Open Source world that problem can only happen with GPL.

How is that not license compatability?

If the license prevents otherwise useful software from being used in the base system, what would you call it?

The term „license incompatibility” is used in situations where you cannot use of a different license in a single program. Usual example is incompatibility between GPL and anything that’s not a subset of GPL.

The situation here is different: it’s about distribution, and it’s up to you, the distributor, to decide whether you want to include restrictively licensed software or not. With license incompatibility, you don’t get that choice: you just cannot legally distribute it.