> My understanding is that someone needs to hold a patent Well, yeah? I mean, the whole definition of a patent is that it gives someone a monopoly over an idea

> My understanding is that someone needs to hold a patent Well, yeah? I mean, the whole definition of a patent is that it gives someone a monopoly over an idea. A patent without someone holding it would be as sensible a concept as a bank account without a holder. A bank account documents that money is owed to someone. If there is noone who it's owed to, then there isn't a bank account. And if there is noone who holds the monopoly ... then there is no monopoly? > What I wonder is if someone who could file a patent or already holds a patent for an idea could put this idea into the public domain without anybody holding a patent? Depends on what you mean by "public domain". If you own the patent, you get to decide who gets to use the patented idea. Obviously, nothing prevents you from deciding that everyone is allowed to use the idea without any further conditions. That you get to decide that is the whole point of the system.