MPEP 2143: The KSR Rationales for Obviousness

Answer in brief

MPEP 2143 lists seven exemplary rationales, drawn from KSR, that can support an obviousness rejection. They range from combining known elements to get predictable results (A) to an explicit teaching, suggestion or motivation in the prior art (G).

What MPEP 2143 covers

Each rationale requires specific findings of fact, which the section spells out with examples.

(A) Combining prior art elements according to known methods to yield predictable results.
(B) Simple substitution of one known element for another to obtain predictable results.
(C) Use of a known technique to improve similar devices, methods or products in the same way.
(D) Applying a known technique to a known device, method or product ready for improvement to yield predictable results.
(E) "Obvious to try": choosing from a finite number of identified, predictable solutions, with a reasonable expectation of success.
(F) Known work in one field prompting predictable variations for use in the same or a different field, based on design incentives or market forces.
(G) Some teaching, suggestion or motivation in the prior art to modify or combine references.

Subsections

2143.01 Suggestion or motivation to modify the references, including when a modification would make the reference unsatisfactory for its intended purpose or change its principle of operation.
2143.02 A reasonable expectation of success is required.
2143.03 All claim limitations must be considered.

How examiners use it

Strong rejections name the rationale and make the findings it requires. Applicants attack missing findings, such as no reasonable expectation of success or a modification that destroys the reference's principle of operation.

On the patent bar

One of the most tested sections. Expect to match a fact pattern to a rationale, and to recognize when a required finding is missing.

Read the full text

Official title: Examples of Basic Requirements of a Prima Facie Case of Obviousness [R-01.2024].

Read MPEP 2143 in full on Wysebridge ↗

Or at the source: USPTO MPEP § 2143.

Questions & answers

What are the KSR rationales?

The seven exemplary rationales in MPEP 2143(I)(A)–(G), from combining known elements with predictable results to an explicit teaching, suggestion or motivation in the prior art.

What is obvious to try?

KSR rationale (E): choosing from a finite number of identified, predictable solutions with a reasonable expectation of success.

Sources for this entry

USPTO — MPEP § 2143 USPTO
Official text of this section, Ninth Edition, Revision 01.2024.
Wysebridge MPEP Center Wysebridge (publisher of this site)
The full MPEP (9th Ed., Rev. 01.2024) free to read, with Wysebridge's estimated patent bar weight for each chapter.

Practical guidance is original editorial content. Company-published figures are the company's own claims and are labeled as such.

Continue this reading path

MPEP 2143.01: Motivation to Combine or Modify MPEP 2144: Supporting an Obviousness Rejection MPEP 2145: Rebutting an Obviousness Rejection

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Cite or share this entry

MPEP.net. “MPEP 2143: The KSR Rationales for Obviousness.” Wysebridge Reference. Content reviewed 9 November 2026.
https://mpep.net/mpep-2143/