Means plus function claims, described in 35 USC 112(f), are a tricky area of patent law. Unlike more commonly used “structural” claims, where “what you see is what you get”; means plus function claims are different. Here, “what you see” is not always “what you get.”
The US and other governments have long realized that it benefits society to grant patents for new and useful inventions. The basic deal is that if the inventor discloses a promising technical innovation, society will reward them with a limited monopoly (called a patent). Ideally, the scope of the patent should roughly correspond to the value of the disclosure.
A patent application has a specification, where the inventor discloses their invention, and a claims section, where the inventor attempts to use words to define the invention’s scope. At the patent office, patent examiners (representing society) evaluate both the specification’s usefulness and the scope of the claims. They then negotiate with the inventor to find a mutually acceptable deal.
There are many different types of inventions. Some inventions can be expressed in precise claim language; others can’t. Mechanical innovations tend to have parts with precisely known and describable structures, and this type of claiming is called “structural claiming.” By contrast, many important inventions, including chemical, biotechnology, and software innovations, have parts that can’t be described at this level of precision. Instead, the parts are better described in functional terms.
Thus, patent law allows both structural and functional claims.
Structural claims (example – simple mechanical inventions): Here, the claim describes the invention’s structure. These claims are more straightforward. What you see is what you get. The legal system interprets the claim broadly. If you can think of a structural claim wording that goes beyond what you invented and is otherwise valid, you can get a broader patent!
Functional claims (means plus function claims, example – biotechnology, complex software): Here, by necessity, the claims describe at least some parts of the invention in functional terms. However, these claims can be tricky and can lead to unintended consequences. Thus, the legal system views this type of claim as having certain pros and cons and places more restrictions here. Legally, the pros and cons of allowing functional claims are:
- Pro: Functional claims encourage invention in new, complex, and valuable areas of technology, where the inventor has invented something new and great, but the area is more complex or less well understood.
- Con: Pure functional claims make it too easy to claim anything, even if the inventor hasn’t invented something. Consider “a drug for curing cancer” with no details. Overuse of functional claims could stifle society with a lot of worthless patents.
- Complications: language is tricky. It is not always clear whether a claim uses structural or functional terms. Many structural components have functional names – consider “screwdriver.”
Ideally, patent law needs a consistent set of functional claiming rules that encourages innovation while not opening the floodgates to bad patents. Easier said than done! The US courts have been grappling with this for over a century. I will summarize some of the present 35 USC 112(f) rules.
Means plus function claim examples
Here are two means plus function claim examples. The first one is easy because it explicitly uses the legally significant word “means.” But the second example is at high risk of also being considered a means plus function claim example as well. This is because even though the term “means” is lacking, the term “device” may be viewed as being an equivalent.
Example 1: A backscratching device, comprising an extension means for extending the reach of a human user’s hand, and a back skin stimulating means attached to a distal end of said extension means.Means plus function claim, with the “means” word clearly evident
Example 2: A backscratching device, comprising an extension device for extending the reach of a human user’s hand, and a back skin stimulating device attached to a distal end of said extension device.Alternative means plus function claim, with “device” standing in for “means”
By contrast, structural claims embed more structural detail into the claim text:
Example 3: A backscratching device, comprising a 1-3 foot long stick, configured to extend the reach of a human user’s hand, and a brush comprising a plurality of stiff bristles, said brush attached to a distal end of said stick, and configured to stimulate the back of said user.Example of a structural claim, with the underlying structure more clearly evident
Summary of means plus function claims
- Unlike structural claims, which can go beyond what you taught, the legal system interprets functional claims as limited by what you taught in the specification. Superficially functional claims may look broad, but they can be narrower than they look. So what you see may be less than what you get. This depends on how “deep” your specification is and more greatly impacts “thin” specifications that lack examples and detail.
- Triggers and traps: The rule is that saying “means” followed by a function will always trigger a functional claim interpretation. Unfortunately, examiners can often argue that some other innocent word is a placeholder or substitute for “means.” They will argue that you didn’t give “sufficient” structure and that they are interpreting this section under 35 USC 112(f). Depending on the specification, you may or may not want to contest this.