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Is Functional Language Permitted in Patent Claims?

A question that comes up frequently is whether functional language is permitted in patent claims. Sometimes this is called functional claiming. This has long been a fundamental yet unresolved issue in patent law. In general, functional language is permitted in U.S. patents and patent applications. But that does not mean it is always acceptable. The acceptability of functional claim language depends on where and how the functional language is used in a given claim and also on how the functional claim language relates to what was actually invented. These questions are often about whether the applicant/patentee’s intentions behind the particular use of functional claim language are proper or not.

To be clear, functional claiming generally refers to describing something by what it does rather than what it is (structurally). Method claims naturally use functional language. The focus here is on functional language in apparatus claims.

The first question to ask is whether the functional claim language is used to recite the point of novelty—the limitation(s) that purportedly distinguish the claimed invention from the prior art. If not, the use of functional language is much more likely to be acceptable and free from dispute. For instance, using functional language in a claim preamble to highlight intended use (possibly in a non-limiting way) is generally acceptable. Though functional recitations appearing anywhere in a claim could still raise concerns. But the situation is most critical when the functional claim language appears right where the claim purports to recite the point of novelty. Suspicions are often raised when a claim includes many structural recitations related to what was already known in the art but then conveniently switches to functional language when setting forth the point of novelty.

When the functional claim language appears at the point of novelty, further analysis is merited. Some other questions should be asked. Is the functional language an attempt to draft a preemptive claim that covers all possible solutions to a technical problem? Or is the functional language an attempt to claim an entire genus of possible solutions? Those are questions about overbreadth in light of the quid pro quo policy underlying modern patent law. This is a matter of preventing an improper extension of a patent’s scope beyond what was actually invented. Also, does the use of functional render the scope of the claim indefinite? This tends to be a concern about whether the functional language makes the claim’s scope unclear by obfuscating what is or is not encompassed. It also reflects concerns about attempts to circumvent the required “peripheral” claim format and instead utilize “central” claiming; that is, attempting to recite merely a vague central inventive concept without informing those of ordinary skill in the art about the scope (outermost boundaries) of the claimed invention with reasonable certainty.

With regard to questions of claim breadth, functional language must be assessed based upon its meaning within the claim as a whole and in light of the entire disclosure of what was actually invented.  This inquiry involves looking at the particular functional claim language in context to see if it is purely functional language or only partially functional language that is limited by associated structural recitations or by the invocation of means-plus-function format (“means for . . . [a recited function]”) specifically authorized by statute (35 U.S.C. § 112(f)).

For example, consider the claim, “An assembly comprising part A, part B, and a connection between part A and part B, wherein the connection is configured to rigidly fix a base portion of part A to an end of part B.” Such a claim seems acceptable even though the “configured to” language is followed by “rigidly fix” language that might be seen as functional if viewed in isolation. In other words, this example uses partly but not wholly functional claim language. The functional recitations are limited by further structural recitations of part A, part B, and a connection.

On the other hand, consider the claim to an improved widget that recites, “A widget configured to achieve good result X.” Such a claim is not structural but instead uses results-based and purely functional language at the point of novelty to try to claim all solutions to a problem.  This latter claim is preemptive of all possible solutions that “achieve good result X”, even those that have not yet been invented. Claims directed merely to a desired result have long been considered objectionable primarily because they cover any means which anyone may ever discover of producing the stated result.

Also, it is possible to add structural recitations such that the functional language is only partially functional. We can continue here from the last example. Consider an amended claim that recites “A widget configured to achieve good result X, comprising:” as merely the claim preamble, and then proceeds to recite the structure that achieves the “good result X” in the body of the claim, such as “substrate Y; and a coating Z applied to the substrate Y, wherein the coating Z comprises a thermally insulating material containing at least 5% yttria by weight.” That claim would not be purely function because of the functional language in the preamble—we can just assume here that “good result X” has something to do with high temperature operation. In this case, the additional structural recitations in the body of the claim would explain what the invention is (in structural terms) rather than stopping with merely a statement of the result it achieves.

There may also be situations where functional-looking language really has a structural meaning (to a person of ordinary skill in the art). For instance, the portmanteau term “screwdriver”—derived from the German word schraubenzieher (screwpuller) and/or the French word tournevis (turnscrew) from the middle ages—could be seen as functional. But, today, anyone would recognize the word “screwdriver” as referring to a generic name for a kind of tool, in a structural way. If we imagine that a patent claim using the term “screwdriver” was presented in the early middle ages, before there was an accepted structural meaning for that term, such medieval usage could raise concerns about its breadth in relation to what was really invented—would it have also covered a pair of pliers that might be used to grip a screw in order to “drive” it, or a hammer? This example in medieval times would look like purely functional claiming of merely a desired result—driving a screw. Whereas, today, usage of “screwdriver” would be an unremarkable structural reference to a genus of tools (having tip that can can engage one of the many different types of screw drives, but excluding pliers and hammers).

A patent claim that uses functional language to refer to an entire genus may (or may not) be acceptable. Genus/species issues are also among the most fundamental in patent law. The philosophical idea behind reference to an entire genus is that it encompasses an unknown or unstated species. For a patentee, this is usually the intent! Patentees often want to get the broadest possible monopoly rights, including blocking rights over later inventions. But a key component of modern patent law is that patents should be limited to what the patentee actually invented. So, very often, questions about the use of functional claim language are about the reasonableness of claim scope that goes beyond what was actually invented (or at least what was actually disclosed in a patent application). These questions often turn on the breadth of the disclosure of an invention and whether that disclosure is robust enough to support a claim covering an entire genus or not. Functional claim language is sometimes used to recite something like a genus rather than merely one or more particular species. A genus recitation may or may not be preemptive. It is a matter of degree and context.

These issues often do not turn merely on whether a given claim uses “configured to” vs. “adapted to” vs. “operable to” language (or the like). Though patent attorneys and judges sometimes try to reduce the larger and more fundamental questions to such superficial formalities—sometimes as a matter of “university discourse” (i.e., making highly ideological policy arguments through the guise of seemingly neutral and objective technical rationales). 

With regard to definiteness or clarity concerns, partially functional language is frequently acceptable and might sometimes be more clear and definite than certain alternative types of claim limitations (like a negative limitation). For instance, with a mechanical invention, partially functional claim language used to recite the way certain enumerated structures are connected and moveable—or not movable—relative to each other may be perfectly clear and uncontroversial. But when purely functional claim language is substituted for structural language such that the (purely) functional language entirely displaces structural language, as a way to consciously avoid limiting the scope of the claim to particular structures, then it might not be acceptable. This is more like the “good result X” or medieval “screwdriver” examples given above. It is the broadness, ambiguity, and overhanging threat of purely functional claiming that is problematic. The public cannot tell what does or does not fall within the scope of the purely functional language.

Another legal issue around functional claim language under U.S. patent law is the use of means-plus-function format (under 35 U.S.C. § 112(f) or pre-AIA § 112, ¶ 6)—also called step-plus-function format for method/process claims. An applicant can invoke means-plus-function claim format to utilize functional language in the claim, in which case the claim language is construed to cover the corresponding structures, materials, or acts described in the specification and equivalents thereof. A catch is that the specification (including the figures) must provide an adequate disclosure of structure corresponding to the means-plus-function claim language. Means-plus-function format can sometimes be useful to recite known (prior art) elements but with recitations at the point of novelty it is often considered a narrow and less desirable claim format. That is because an equivalent structure for means-plus-function purposes must have been available at the time of the issuance of the claim, but does not extend to after-arising technology developed after the issuance of the patent (except under the the Doctrine of Equivalents, if it applies).

There have been many, many cases that deal with functional claiming. However, U.S. courts have not not definitely and conclusively resolved these issues. That is not really surprising because patent applicants have numerous incentives to try to obtain monopoly rights over more than what they invent.

In the USPTO’s Board of Patent Appeals and Interferences’ (BPAI) precedential case Ex parte Miyazaki (which now seems abrogated, at least in major part), it was explained that “when [a] limitation encompasses any and all structures or acts for performing a recited function, including those which were not what the applicant had invented, the disclosure fails to provide a scope of enablement commensurate with the scope of the claim . . . .” Such purely functional claim language is unpatentable unless the applicant has given the public notice that the limiting conditions of 35 U.S.C. § 112, sixth paragraph (now § 112(f)) are being invoked. Therefore, according to Miyazaki, purely functional claim language is unpatentable when it is “unlimited either by (1) the application of 35 U.S.C. § 112[(f)], or (2) the additional recitation of structure.” (emphasis in original).

Where this has been complicated is that the Federal Circuit has (controversially) held that purely functional language that does not use “means for” to explicitly invoke § 112(f) might still be interpreted as means-plus-function language. This stands in contrast to the more convincingly-argued BPAI Miyazaki decision regarding the need for notice to the public regarding invocation of § 112(f) limitations. The Federal Circuit is trying to save applicants from themselves (and potentially from the invalidity or unpatentability of the purely functional claims they chose to pursue) at the expense of the general public’s entitlement to clarity and predictability regarding the scope and validity of patent claims. This is also another example of Federal Circuit hostility to Supreme Court precedent regarding breadth- or preemption-related invalidity issues.

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Austen Zuege is an attorney at law and registered U.S. patent attorney in Minneapolis whose practice encompasses patents, trademarks, copyrights, domain name cybersquatting, IP agreements and licensing, freedom-to-operate studies, client counseling, and IP litigation. If you have patent, trademark, or other IP issues, he can help.