Another Example of the Peril of Functional Language in Patent Claims

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Patent practitioners have long relied on functional language such as “configured to,” “adapted to,” and “capable of,” as a strategy for broadening claim scope by using such terms to capture a structural range of elements that can perform a function rather than one specific configuration. However, this tactic comes with risks of unintended judicial interpretation when such terms are not used with a clear structural foundation. A recent nonprecedential decision by the U.S. Court of Appeals for Federal Circuit (Federal Circuit)—Blue Buffalo[1]—serves as a reminder that when functional terms are used without precise intent, this strategy can backfire.

Blue Buffalo appealed a decision of the Patent Trial and Appeal Board (PTAB) that affirmed an Examiner’s rejection of certain claims its application for obviousness. Claim 1 of the Blue Buffalo application recited a packaged food product comprising a container, including at least one sidewall and a bottom wall to form a storage area, and a food product retained within the storage area, where “the at least one side wall is configured to be readily deformable” and a tool portion is “configured for use in breaking up and/or tenderizing the food product.” The PTAB construed the “configured to” and “configured for” claim language as meaning merely “capable of” performing the recited functions.

In the appeal, Blue Buffalo argued that “claim language that employs ‘configured to’ type language should be interpreted to cover devices that are specifically designed to perform the stated function.” In particular, Blue Buffalo asserted that the claims require that the apparatus is specifically designed to deform the sidewall and use the tool portion for breaking up food. If this narrower interpretation of “configured to” was accepted, the prior art might not have met the claim limitations, potentially overcoming the obviousness rejection.

However, the Federal Circuit agreed with the PTAB’s adoption of a broader interpretation of “configured to” and “configured for” as meaning “capable of.”

The Federal Circuit referred to and distinguished two of its prior cases to illustrate why the broader construction was warranted. In In re Giannelli[2], the court construed “adapted to” in a rowing machine claim to mean the apparatus was “designed or constructed to be used” in a specific manner, noting that the written description supported this narrower meaning. Similarly, in Aspex Eyewear[3], “adapted to” for magnetic members was interpreted narrowly because the specification indicated an intent for actual engagement with a spectacle frame. Further, the patent specification used “capable of” elsewhere, suggesting a deliberate distinction.

The Federal Circuit found both cases distinguishable. The critical differences were both terminological and contextual. First, the precedent involved “adapted to,” not the “configured to” language present in Blue Buffalo’s claims. While the terms can be related, the Federal Circuit treats them as separate lexical units for claim construction purposes. Second, the narrower constructions in Giannelli and Aspex Eyewear were driven by contextual clues within the respective patent specifications and claim sets. The specifications in both cases affirmatively suggested a design-purpose meaning.

In contrast, Blue Buffalo’s application offered no such intrinsic support. The Federal Circuit explained that “Blue Buffalo points to nothing in the claims or written description suggesting that ‘configured to’ should be construed more narrowly than ‘capable of.’” The specification merely described a sidewall that is “readily deformable” and projections that allow the tool to “break up and/or tenderize food product,” which describes capability, not specific design intent.

This analysis reinforces a fundamental principle of claim construction that the specification is the primary guide to the meaning of claim terms. When a patentee seeks a narrow, purpose-driven construction for a functional phrase like “configured to,” the patentee must specify the limitation in the description. The Federal Circuit will not infer a “specifically designed to” limitation simply because an applicant argues for it during prosecution. The intrinsic evidence must lead there. The Federal Circuit found no such mandate for a narrow reading in the specification.

Thus, the Federal Circuit’s decision in Blue Buffalo provides a clear, narrow lesson in the interpretation of functional claim language: a “specific design” limitation may not be imported into the terms “configured to” or “configured for” absent clear intrinsic evidence. The opinion underscores that functional claim terms are not interpreted in a vacuum but are given meaning through the lens of the entire patent application.

By tethering the “configured to” analysis to the intrinsic record, Blue Buffalo reaffirms the Federal Circuit’s longstanding framework for interpreting claimed functional language. For example, in the Federal Circuit’s precedential decision in In re Man Mach,[4] the Federal Circuit interpreted the claimed phrase for a remote control: “a thumb switch positioned on the top side of the body, the thumb switch being adapted for activation by a human thumb” as being “configured to,” i.e., as “being made or designed for activation by a human thumb.” The narrow interpretation was based on the specification that described how the body of the remote control device is preferably elongated and rounded to be held in the hand.

Functional language, such as “configured to,” “adapted to,” and “operable to,” is also discussed in the MPEP in §2111.04, §2173.05(g), and §2181-2183. Such language may invoke 35 U.S.C. § 112(f), although “configured to” and “adapted to” generally do not trigger the narrow interpretation of structure/function in mean-plus-function claims. The MPEP distinguishes between intended use language (which may not limit structure) and capability-based functional language (which can limit structure). According to MPEP 2114.04, “[a]pparatus claims cover what a device is, not what a device does.” This means that the capability of a prior art device to perform the claimed function is often sufficient to anticipate the claim, regardless of whether it’s explicitly stated to be “configured to” perform that function. As demonstrated by the selection of cases discussed above, determination of whether or not structural limitations carry with claimed functional language depends on the specific facts of the case.

In summary, the term “adapted to” has, in some cases, been construed narrowly when the specification supports a design-purpose meaning, but it is not immune to a “capable of” reading absent such support. “Configured to” is increasingly treated as synonymous with “capable of” or “operable to” in the absence of explicit contextual clues. When drafting, consider using “configured to” if you intend to claim a capability or a structural configuration that can perform a function or “adapted to” if you wish to signal a more purposeful design limitation, when the narrow meaning is supported throughout the specification. Further, if a functional phrase is desired to be interpreted as “specifically designed to,” the detailed description should describe this. Finally, if “configured to” is used in the independent claims, avoid switching to “specifically structured to” in dependent claims unless intending to add a limitation. The key lesson concerning the use of functional language is that if a specific function is intended, that specific function must be adequately described. There must be support in the specification.