[otterley]

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.

[promano]

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

[odo1242]

Yea - software released under the BSL is “source available”, not open source.

[otterley]

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.

[robertlagrant]

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.