Being a roboticist, a song writer, and someone interested in economics and politics means that I almost never go a week without running into the term "Intellectual Property" at least once. The first thing that's interesting about that is that it's a relatively new term that was coined in the 1960s, the decade when the World Intellectual Property Organization (WIPO) was founded, and even then wasn't in widespread use for another couple of decades.
Before that, it seems, it was commonly agreed that one could own a patent, and therefore a patent was a type of property. On the other hand, it wasn't generally thought that the intellectual creation that formed the knowledge on which the patent was based was property. Nowadays, the phrase Intellectual Property has distorted the language sufficiently such that many people believe that intellectual creations are indeed property and are double-plus good.
My belief is that intellectual creations and knowledge are not usually property without completely distorting the meaning of the word 'property.' In order to argue this point, I'm going to focus on just one aspect of intellectual creations as an example: the creation of knowledge that forms the "meat" of method patents. I'm also going to focus on a single attribute of property: that it can be stolen. If something cannot be stolen, as defined by law, then it's not property.
Let's say Joe invents a method. Let's say it's only in his brain and notes and that he hasn't disclosed it to anyone else. Does he, at that moment, own the invention? Not really, I would say. First, Jack, John, Jill and June might have already also invented the method independently or will soon. Indeed, most inventions are not patentable because they fail the non-obviousness criterion. Even the ones that are deemed adequately non-obvious still are, or would be, invented independently by multiple people or entities.
If the invention is ever property, it is at that moment when it is a trade secret, and if and only if nobody else has also come up with the same invention and disclosed it. At the moment, the undisclosed knowledge can be stolen and therefore it can potentially be thought of as property. Someone could torture Joe until he discloses the invention (very unlikely); someone could break into his office and steal his notes and learn of the invention that way (pretty unlikely - have you ever tried to read an inventor's notes?); or someone could bug his office and eavesdrop on him discussing the invention with someone else (rather unlikely). However, trade secrets are typically lost when a rogue employee distributes them without permission and that does happen once in a while. At the moment, if Joe is really the only one to have come up with the invention and if Joe has not disclosed it publicly, then it can potentially be stolen and I'll concede that it is, at that moment, plausibly a type of property. Even so, a trade secret is just a type of secret, and I'm not sure that secrets, while perhaps quite dear to the originator, are really property.
They say Necessity is Mother of Invention. I say Progress is the Father of Necessity in that as new knowledge and products are created so are new needs (part of the process of Creative Destruction). Supporting Technology is the Father of Invention. Engineers and Scientists (and others) are the Siblings of Invention and we all live in the same great big happy and competitive family and are nearly simultaneously exposed to the same Necessity, state of Progress, and Supporting Technology. In other words, many of us are driven to invent more or less the same thing more or less at the same time. I've never seen an invention that nobody else would have ever invented if the particular inventor who first figured it out had not. Of course, I haven't looked through all of the many millions of patents worldwide or considered the far larger body of non-patented inventions, but I've seen quite a few and that's my impression.
Most of the time, it makes no sense to patent an invention. For example, I've invented hundreds of methods in the realm of robotics but have only patented between ten and twenty of them. Perhaps the invention is too obvious so you can't get a patent; perhaps it's so non-obvious that disclosing it in a patent is counterproductive because the disclosure would give the competition a step up that it wouldn't otherwise have; perhaps the value of the invention is less than the cost to file, maintain, and enforce the patent; perhaps the inventor or company just doesn't have enough money or other resources to pursue a patent even if it would be well worth the cost; and so forth.
Are these non-patented inventions property and if so, whose property is it? If Joe's non-patented invention is disclosed, either because he uses it in a commercially available product and the invention is readily deduced from looking at the product or he otherwise causes its disclosure, then everyone learns about it and can use it for any purpose. We don't consider this dissemination and use to be theft or to be illegal, unethical, or immoral in any sense, so I find it hard to consider Joe's invention to be property of any kind. Again, the principle is: if you can't steal it, it isn't property.
Let's say Joe's invention is sufficiently non-obvious and novel to qualify for a patent and he writes the patent and files it and he is the first of the inventors to file (even though the others may have invented it first). Is the invention property now? No. It's the same deal. Until the patent issues (and it might never issue for a variety of reasons), anyone can use the disclosed invention for any purpose. In addition, it's likely that the patent will publish and disclose the invention well before the patent is issued. Again, anybody can use the disclosed invention for any purpose until the patent issues. Again, it's not stealing, therefore it's not property.
Let's say Joe's patent finally issues today. Yesterday, the invention wasn't property. Is it property now that the patent has issued? No. The patent is the property. The patent is a type of Government Originated Legally Enforced Monopoly (GOLEM) (and a GOLEM, in turn, is a type of Government Originated Legally Enforced Restriction on Trade (GOLERT)). The patent is what's sold, licensed, or bartered. The invention is still disclosed and known by many people. They can still build on the knowledge or work to circumvent the knowledge. They can still even use the knowledge for certain non-commercial purposes. The thing of value is the GOLEM and that was created by the government out of thin air. You still can't steal the invention since it's been freely disclosed, therefore the invention is still not property. It's the GOLEM that's property and that property restricts others from using the publicly disclosed invention.
Eventually Joe's patent expires. One day Joe has the right, via the GOLEM, to control most uses of the invention. The next day he doesn't. The invention, which wasn't property one day is definitely not property the day after the patent/GOLEM expired. Now it definitely can't be stolen.
In summary, the only time the invention is plausibly property is prior to when the first inventor discloses it (either intentionally or accidentally). After that, the invention, the intellectual creation, the method, is not property.
The patent is the property.