Crash course on patents: The effects of holding a patent

In this document

The rights granted by a patent
The scope of a patent

The rights granted by a patent

Using the invention

A patent gives its owner the right to exclude others from using an invention. Strictly speaking, it does not grant its owner the right to use the invention himself, since there may be other patents held by others that are necessary for that. For example, to build a car you need an engine, a transmission and wheels. Each of these could be protected by one or more patents held by different entities. This would mean that none of them could build a car without the permission of the others. However, any of them could stop an outsider from building a car.

The rights to the invention held by the patent owner are typically formulated very broadly. US law sums it up very nicely by granting the owner the right to "make, use or sell" the invention.

Commercial and noncommercial use

In most European countries, the exclusive exploitation rights granted by a patent are restricted to commercial exploitation. A private person who builds the patented invention in his own home for his own personal goals cannot infringe on a patent. The reasoning behind this is that such a situation cannot harm the patent holder.

US law is more strict. It forbids anyone from making, using or selling the invention, even when the use is strictly personal. Of course, since patent infringement lawsuits are very expensive, a private person is rarely if ever prosecuted for using the invention in his own home. Such a situation could occur when a private person offers on his website a piece of software that uses someone else's patented technology. The patent holder may feel that the freely available software threatens his commercial product, and then decide to use the patent to prevent the distribution of the free product.

Studying the invention

It is always permissible to use a patented invention for research purposes. Such study may give new insights in possible uses of the invention, or possible alternatives to what is described in the patent. This might even result in new patents for the alternatives, or in workarounds.

Of course, the "research" should not simply be a commercial exploitation in disguise.

The scope of a patent

The claims

Claim drafting and interpretation is an arcane art. Over the years courts have interpreted claim language more strictly. In response, patent practitioners have taken to using more generic terms and legally more secure phrasing. For instance patents today more and more often use functional terms ("means for receiving an electrical signal" rather than "an antenna").

Something infringes a patent if it has all the elements of a claim in the patent, or performs all the steps of a claim. It does not have to match all the claims, a single one will do. However, it is important that it matches all elements in that single claim. Most patent courts take this requirement quite strictly and will not easily ignore an element in a claim unless it is clearly irrelevant. One often-heard argument against ignoring an element is that patent writers are aware of the strict interpretation and so would not put in an element unless necessary. Therefore, an element that is present in the claim must have been deemed necessary and so may not be ignored.

Infringement through equivalence

In practice, claim infringement determination is not quite as simple as this. Often elements in the claim are not literally the same as in the allegedly infringing product. As this could lead to unfair situations, most countries have developed the so-called doctrine of equivalence. When using this doctrine, the courts determine if the feature in the allegedly infringing product is an equivalent of the element in the claim. When something is an equivalent is something that strongly depends on the wording of the patent and the state of the case law at the time. For example, if the patent clearly states "The word 'water' in this specification should be read as meaning any fluid with property X", then any fluid with property X is seen as an equivalent of 'water' for the purpose of determining infringement.

The more well-known it is that certain elements have equivalents, the less likely it is that a court will accept infringement under the doctrine of equivalence. For example, everyone knows a nail is equivalent to a screw, and that the accepted general term is 'fastening means'. If a claim then nevertheless mentions the use of a nail to connect two elements, the chance that a court will rule the use of a screw to be equivalent is small. After all, when the patent does not use the general term, the author must have had a reason to use the specific term.

Unfortunately, the concept of equivalence and how it is applied varies greatly from country to country and from patent to patent. Sometimes new laws or case law significantly change the scope of a patent.

Other relevant factors

Another complicating factor is that often during the prosecution at the various patent offices, the applicant will present arguments showing that the elements in the claim are different from those in the prior art, to overcome an objection that the claimed invention is not novel. So, for example, the applicant may argue that, in this invention, 'nail' should be read specifically as a nail, which makes it different from the prior art which uses a screw. If this is successful, he will be granted a patent that mentions 'nail' as an element in the claim.

However, he should not be able to then prosecute an infringer who uses screws instead of nails. This is referred to as 'file wrapper estoppel' or 'prosecution history estoppel'. In practice, it means that you have to study the correspondence between applicant and patent office to determine if any such arguments have been made.

There are also more specialist issues, such as the priority date of the patent and the individual claims. However, these are very difficult.