John Stewart Mill described "natural monopolies (meaning thereby those which are created by circumstances, and not by law)" as arising due to the limited supply of Land with particular characteristics, and Labour with particular unique abilities or skills. He described "artificial monopolies" as those created by government "to confer a monopoly upon a producer or dealer, or upon a set of producers or dealers ... to give them the power of levying any amount of taxation on the public, for their individual benefit, which will not make the public forgo the use of the commodity". (Mill, J.S. 1848. The Principles of Political Economy)

There is debate about whether natural monopolies exist at all. The issue at play might actually be concern with negative externalities from redundant overlapping and incompatible infrastructure, or excess demand upon a limited resource. But there are usually ways to avert such problems through standardized interoperability, or equitable management of access rights, both of which can be achieved through intelligent regulation. Open standards and shared access are often a workable option in scenarios that are assumed to be natural monopolies. If for some reason these routes were never explored, or were considered but not chosen, this would result in artificial monopolies, not natural ones.

One type of artificial monopoly created by government is a multi-year authority for a person or organization to issue and enforce the payment of private taxes in relation to any implementation a useful, novel, non-obvious, documented idea. When we come to name that rule by the word "patent", it seems to take on in our minds the character of a material thing, instead of a private taxation privilege granted by the state, especially when we speak of "patent owner", rather than "patent beneficiary". Alfred North Whitehead described the fallacy of misplaced concreteness as the mistake of confusing an abstract concept, which is a construct of the mind, with a genuine or hypothetical physical entity.

When we refer to an "owner of a valid patent", it is easy even for a libertarian to feel that this is notionally equivalent to the owner of a registered car, or of a UL-certified electric device, holding custody of a physically concrete thing that has also passed some sort of validation. On the other hand, when we refer to a "beneficiary of a private taxation privilege granted by the state" it's more straightforward for a libertarian and everyone else to see this as a constraint upon free market operations. The government's intent may be to achieve some socio-economic purpose by granting producers the right to autonomously levy taxes for their individual benefit. But it is important to realize always that it provides the beneficiary a different form of revenue than that which arises from the sale of goods and services.   

For clarity, therefore, within this syllabus we use descriptive language such as "artificial monopoly" rather than the word "patent".