6.3 Special Claim Formats: Means-Plus-Function & Markush Claims
Key Takeaways
35 U.S.C. § 112(f) allows functional claiming but restricts claim scope to the corresponding structure described in the specification and structural equivalents thereof.
Using 'means for' creates a rebuttable presumption that § 112(f) applies, while omitting 'means for' creates a rebuttable presumption that § 112(f) does not apply.
Software claims invoking § 112(f) require an explicit algorithm (flowchart, pseudocode, or formula) in the specification; failure to disclose an algorithm results in § 112(b) indefiniteness.
Markush claims group alternatives ('selected from the group consisting of A, B, and C') and require members to share a single structural similarity or common utility.
Product-by-process claims are evaluated during examination based on the physical product itself, while Jepson claim preambles constitute binding admissions of prior art.
6.3 Special Claim Formats: Means-Plus-Function & Markush Claims
Patent law permits several specialized claim formats designed to address specific technical situations—including functional combinations under 35 U.S.C. § 112(f), chemical/material groupings via Markush claims, structural products defined by manufacturing methods (product-by-process claims), and improvement inventions (Jepson claims).
35 U.S.C. § 112(f) Means-Plus-Function & Step-Plus-Function
Under 35 U.S.C. § 112(f) (pre-AIA sixth paragraph):
"An element in a claim for a combination may be expressed as a means or step for performing a specified function without the recital of structure, material, or acts in support thereof, and such claim shall be construed to cover the corresponding structure, material, or acts described in the specification and equivalents thereof."
The 3-Prong USPTO Examination Test (MPEP 2181)
An examiner will construe a claim limitation under 35 U.S.C. § 112(f) if and only if all three prongs of the following test are met:
- The claim limitation uses the phrase "means for" or "step for" (or a recognized nonce word acting as a substitute for means).
- The phrase "means for" or "step for" is modified by functional language.
- The claim limitation does not recite sufficient structure, material, or acts to perform the specified function.
Presumptions and Nonce Words (Williamson v. Citrix)
- The "Means" Presumption: Use of the term "means for" creates a rebuttable presumption that § 112(f) applies. Omitting "means for" creates a rebuttable presumption that § 112(f) does not apply.
- Rebutting the Presumption: In Williamson v. Citrix Online, LLC, 792 F.3d 1339 (Fed. Cir. 2015), the Federal Circuit eliminated the "strongly presumed" standard. If a claim omits "means" but uses a generic nonce word (e.g., module for, mechanism for, unit for, element for, device for) coupled with functional language without reciting structure, the presumption against § 112(f) is rebutted, and § 112(f) applies.
Software & Computer-Implemented Inventions: The Algorithm Requirement
When § 112(f) applies to a computer-implemented function (e.g., "means for processing financial transactions"), disclosing a general-purpose computer or microprocessor in the specification is insufficient.
The Algorithm Requirement: For software claims under § 112(f), the specification must disclose a specific algorithm (expressed as a flowchart, pseudocode, mathematical formula, or sequential steps) to perform the recited function (Aristocrat Techs. v. Int'l Game Tech.).
If no algorithm is disclosed in the specification, the claim is indefinite under 35 U.S.C. § 112(b) because the claim lacks corresponding structure linked to the function!
Markush Claims (MPEP 2173.05(h) & MPEP 803.02)
A Markush claim defines an element using a closed group of specified alternatives:
Proper Markush Grouping Requirements
To be proper, the members of a Markush group must share:
- A single structural similarity (e.g., members belonging to a recognized chemical class sharing a common structural core), OR
- A common utility or physical property.
Improper Markush Rejections & Election of Species
If the members of a Markush group are patentably distinct (e.g., grouping an organic solvent, a digital sensor, and a ceramic brick with no common property), the examiner issues an improper Markush rejection under § 112(b) or requires an Election of Species under 35 U.S.C. § 121, forcing the applicant to select a single species for search.
Product-by-Process Claims (MPEP 2113)
A product-by-process claim defines a structural product by its method of manufacture (e.g., "A semiconductor wafer produced by the process of steps A, B, and C").
Patentability Standard vs. Infringement
- USPTO Examination Standard (Patentability): During prosecution, a product-by-process claim is evaluated for patentability (§ 102 novelty / § 103 nonobviousness) based on the final physical product itself, NOT the process steps (In re Thorpe). If the resulting physical product is identical to or obvious over a prior art product, the claim is rejected—even if the prior art product was made by a completely different process!
- Litigation Standard (Infringement): For court litigation, the Federal Circuit held in Abbott Labs. v. Sandoz that process terms in a product-by-process claim serve as actual limitations; an accused product only infringes if it was manufactured using the claimed process steps.
Jepson Claims (MPEP 2129)
A Jepson claim is an improvement claim format that explicitly delineates prior art from the applicant's novel contribution:
- Preamble: Recites what is old/known in the prior art ("In an automotive braking system having a master cylinder and brake lines...").
- Transition: "the improvement comprising:"
- Body: Recites the new structural element ("a ceramic piston disposed within...").
Binding Prior Art Admission: The preamble of a Jepson claim constitutes an implied binding admission by the applicant that the preamble elements are prior art. The applicant cannot later argue during prosecution or litigation that preamble subject matter is novel.
An independent software claim recites 'a processing module configured to execute financial calculations.' The claim does not use the word 'means.' Under Williamson v. Citrix Online, LLC, how should the USPTO examiner evaluate this limitation?
The absence of the word 'means' creates an absolute, irrebuttable guarantee that 35 U.S.C. § 112(f) can never apply.
Because 'processing module' is a generic nonce word coupled with functional language without reciting structure, the presumption against § 112(f) is rebutted, and § 112(f) applies.
The examiner must reject the claim under § 101 for lacking patent-eligible subject matter before evaluating § 112(f).
The claim is automatically converted into a product-by-process claim under MPEP 2113.
A patent application claims a computer system invoking 35 U.S.C. § 112(f) for 'means for sorting encrypted database records.' The specification describes a general-purpose CPU connected to a memory, but does not describe any specific algorithm, flowchart, or logic steps for sorting encrypted records. What rejection must the examiner issue?
Reject the claim under 35 U.S.C. § 102 for anticipation by general-purpose CPUs.
Reject the claim under 35 U.S.C. § 112(c) for improper single dependency.
Reject the claim under 35 U.S.C. § 112(b) for indefiniteness because computer-implemented § 112(f) claims require disclosure of a specific algorithm in the specification.
Allow the claim, because disclosing a general-purpose CPU provides sufficient structure for any computer-implemented means-plus-function limitation.
During examination of a product-by-process claim reading 'A ceramic engine valve produced by the process of sintering powder A at 1500°C for 4 hours,' the examiner finds a prior art reference disclosing an identical ceramic engine valve made of powder A sintered at 1200°C for 8 hours. How must the examiner evaluate patentability under MPEP 2113?
Reject the claim under 35 U.S.C. § 102 or § 103 because patentability of product-by-process claims is determined by the physical end product itself, regardless of novel process steps.
Allow the claim because the applicant's sintering temperature of 1500°C is novel over the prior art temperature of 1200°C.
Convert the claim into a Jepson claim and demand an election of species.
Reject the claim under 35 U.S.C. § 112(f) for lacking structural equivalents.
An applicant uses a Jepson claim format: 'In a bicycle frame having a top tube, down tube, and seat stay, the improvement comprising a carbon-fiber reinforced bottom bracket shell.' What is the primary legal consequence of using this format during prosecution?
The claim is automatically limited under 35 U.S.C. § 112(f) to the disclosed carbon-fiber manufacturing method.
The USPTO will assess a double dependent claim fee surcharge for combining preambles.
The claim is subject to an automatic restriction requirement between the frame tubes and the bottom bracket shell.
The preamble elements (top tube, down tube, and seat stay) constitute an implied binding admission of prior art by the applicant.
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