It is absolutely true that a work can be in the public domain and not have source available (or even contributable). But that doesn't really matter to most people. The question for most people is not whether something is open source, but whether they can copy and make use of a work without being held liable for copyright infringement. SQLite happens to be both public domain and open-source to an extent (i.e., source available).
Conversely, open source doesn't necessarily mean "free to use without encumbrance." There are many open-source licenses that forbid certain uses (e.g. Business Source License). On the other hand, a work in the public domain is free to be used by all without restriction.
A better analysis of open source vs. public domain would be in the form of a square, where one dimension would be the right to use the work, and the other dimension would be the ability to obtain and contribute source code.
The Business Source License is not an open source license. Open source does mean "free to use without encumbrance" - see points 5 and 6 of the Open Source Definition at https://opensource.org/osd
Approximately zero people who make real business decisions care what the OSI considers a "real open-source license" to be. They care what the text of the license says.
Also, many licenses, such as the GPL (one of the very first "open source" licenses), have certain encumbrances; you cannot redistribute GPL-licensed software without either including its source code or making it readily available.
No one's saying public domain isn't useful. You're replying to a comment that's specifically and solely combatting the idea that public domain means open source.
Any definition of open source that doesn't include the public domain is out of touch with how real people use the words "open source" and is therefore useless. You can make up any definition you want, but if you insist on calling elephants "bananas", I'm not going to take you seriously
The problem with your analogy is that open source has a definition. As does public domain. As do elephants and bananas.
In your analogy we're not the ones calling elephants bananas, you are. We want to keep calling one bananas and the other elephants. You are suggesting that since elephants are similar to bananas you can simply use either word.
Legally, Open Source and Public Domain are -very- different animals. Open Source comes eith a copyright, and a license (which has requirements), public domain does not.
Of course public domain and open source are both "shipped as source code". Then again so is a fair bit of proprietary software. That doesn't make it open source either.
How people use the term "fair use" is out of touch with the legal definition. That doesn't change the legal definition, it means people use the term incorrectly.
It means the common use of "fair use" is different to the legal definition. It doesn't mean either are wrong. It isn't wrong to say a tomato is a vegetable. In common use it is.
Similarly the common use of "open source" is different to the OSI's preferred definition. Note that the OSI's preferred definition is not a legal definition. It's just what they prefer.
I read the text: it's license hermenuetics at best and FUD at worst. Has there been a single instance in recorded history of the author of a public domain work trying to enforce usage, modification, or distribution permissions. Sure, you can point to theoretical variation in the precise semantics of the public domain in various jurisdictions, but it feels like a bar exam puzzle, not a real world practical concern. In the real world, you can safely do whatever you want with public domain software. It counts as free software. That half the planet nowadays uses SQLite and treats it as free software is testament to this reality. Obscure license pedanticism just doesn't inform the choices of anyone actually building.
Open source and Free software have different philosophies, but in practice they are essentially the same. You are thinking about copyleft vs non-copyleft. BSD, MIT, CC0 are all Free Software licenses but not copyleft.
You’re making the common mistake of confusing the copyleft vs. permissive distinction with the free software vs. open source distinction.
GPL is copyleft. MIT, BSD etc. are permissive. But all of those are both free software and open source, which are essentially synonyms.
The reason so many people get confused by this is that some of the people who prefer copyleft licenses (notably the FSF) also tend to prefer the term “free software”, for philosophical reasons.
It might seem really unlikely any acquirer would ever sue, but if your big company has compliance auditors they will need to see something in black and white.
