In common-law jurisdictions, for something to be enforceable as a contract there must be three things: an offer, acceptance, and consideration (something valuable gained by both parties). Because most users did not pay for open source software, when they download it there is no consideration to the licensor. Therefore their license to use it is not enforceable as a contract; it is what's known in law as a bare license. Bare licenses are not as strong as contracts; in particular, the licensor can revoke a bare license at any time.

In short, it is very risky to use open source in the USA, UK, Canada, Australia, etc. without additional legal framework (such as drawing up a contract with the author) because the author of the OSS you use can revoke your license at any time, for any reason. This has not been actually tested in court yet, but it is a concerning wrinkle of contract law in those jurisdictions.

> What else would they be

The common answer is that a copyright license are only a pure set of permissions that enable a person to do something which otherwise would make an activity illegal.

A contract in contrast is an agreement between minds that defines rights and duties of the parties.

In addition, a copyright license can only give permission for activity which copyright law make illegal. It is limited to be within the scope of what copyright law already restrict. A contract on other hand is only limited by contract law. A typical restriction on contract is that you need to be an adult of legal capacity, ie not a child or under a legal guardian. If a software license is governed by contract law then those restrictions would suddenly apply to software licenses, and the scope of a copyright license could go beyond that of copyright law, both which sounds strange unless contract law has specific rules in places for copyright licenses.

My guess is that french contract law actually have specific rules for copyright licenses, in which case it is more similar to copyright law of other countries but simply placed under the heading of contract law.

It is very far from the norm, both in US and international law. The only things in common are they are written down, and involve obligations.

The key difference is that a license implies obligations on only one party (not the copyright holder), and they do not need to have signed or agreed to anything to be obligated. There is no requirement to exchange value for license provisions to bite.

You can make a contract around granting a license if you like, but that is wholly up to the copyright owner.

Another key difference is that copyright ownership cannot be transferred without a physical written paper identifying itself as such.

Many lawyers and judges are very unclear on copyright law, and say confused things like you did. That is not law.

> It is very far from the norm, both in US and international law. The only things in common are they are written down, and involve obligations.

Mind citing?

The US Constitution and the Berne Convention are both readily available to read.

In the Constitution, copyright gets its own section.

What else would licenses be if not contracts?

The could be something something else: documents granting you certain permissions and denying others in a unilateral way, whether you agree or not.

"Contract" could be defined in such a way that such documents are not covered under definition. If a contract is some agreement that two parties negotiate and sign off on, then a copyright license isn't a contract.

> What else would licenses be if not contracts?

In Anglo-American law, at least, a license is a permission which may either be gratuitous (most open source software license usually would fall into this category) or part of a contract (which requires mutual consideration, among other things, rather than a one-sided grant).

But, IIRC, gratuitous licenses are, in US copyright, enforced under contract principles, mutatis mutandis, not under the bare law otherwise applicable to the rights transferred. And I think the FSF is very much aware of that, and that is a big reason for the automatic termination on breach provisions of the GPL, to get back to the bare law, no license situation, at least after an established breach.

No. A gratuitous software license is a bare license. Because the licensor gets nothing, nothing is binding upon them. They may alter the terms of or revoke the license at any time, even notwithstanding promises in the license not to do that (as in the GPLv2).