Patent bar Obviousness (35 U.S.C. 103) question: examiner proposes replacing the piston with a rotary vane

Patent barObviousness (35 U.S.C. 103)

The primary reference teaches a pump that works only by drawing fluid with a reciprocating piston. To reach the claimed invention, the examiner proposes replacing the piston with a rotary vane, which would change the pump's basic principle of operation, relying on a second reference that teaches vane pumps generally. Which argument by the applicant is strongest?

A The rejection fails because the claim recites a pump and pumps are always analogous art
B The second reference cannot be combined because it was not cited by the primary reference
C The combination is improper because the examiner did not physically build it
D The change would alter the primary reference's principle of operation
E The references cannot be combined because they were published in different years

Show the answer and explanation

Answer: D. The change would alter the primary reference's principle of operation

Answer: The change would alter the primary reference's principle of operation. If a proposed modification would change the principle of operation of the prior art invention being modified, the teachings of the references are not sufficient to render the claims prima facie obvious (In re Ratti; MPEP 2143.01(VI)). A related rule says a modification may not render the prior art unsatisfactory for its intended purpose (MPEP 2143.01(V)). Why not the others: - Not cited by the primary reference: references need not refer to each other to be combined. - Different years: publication dates do not prevent combination. - Physical construction: obviousness does not require building the combination. - Always analogous: whether art is analogous does not cure a modification that changes the principle of operation. Rule: A modification that changes the reference's principle of operation does not support obviousness. Source: MPEP § 2143.01 (9th ed., Rev. 01.2024); 35 U.S.C. 103; as at Oct 2026

Common mistake

Arguing that references must cite each other to be combined.

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Original study material written from the MPEP; not a question from the current exam.Independent. Not affiliated with or endorsed by the USPTO. Verify figures and rules against current guidance before relying on them.