Obviousness Rejections: Building Multi-Reference Combinations for Invalidity

When a patent examiner or challenger argues that a claimed invention is obvious, they rarely rely on a single prior art reference. Instead, they build what practitioners call obviousness invalidity combinations, pulling together two, three, or even more prior art documents to argue that a skilled person would have combined them to arrive at the claimed invention. Understanding how these combinations are structured, challenged, and defended is essential knowledge for patent attorneys, inventors, and anyone navigating the patent prosecution or litigation process.

This article walks you through the legal foundation, the building blocks of a strong combination, the most common pitfalls, and how to respond effectively when such rejections land on your desk.

What Is an Obviousness Rejection Under 35 U.S.C. 103?

An obviousness rejection arises when an invention, though not identically disclosed in a single prior art reference, would have been obvious to a person having ordinary skill in the art (PHOSITA) at the time the invention was made. The governing statute in the United States is 35 U.S.C. Section 103, which states that a patent may not be obtained if the differences between the claimed invention and the prior art are such that the invention as a whole would have been obvious.

The landmark Supreme Court decision in KSR International Co. v. Teleflex Inc. (2007) significantly broadened the framework for obviousness invalidity combinations. The Court rejected a rigid application of the older TSM test (Teaching, Suggestion, Motivation) and instead embraced a more flexible, common-sense approach. After KSR, examiners and courts can rely on the following rationales to combine references:

Combining known prior art elements using known methods to yield predictable results
Simple substitution of one known element for another to obtain predictable results
Using a known technique to improve a similar device or method in the same way
Applying a known technique to a known device ready for improvement
Choosing from a finite number of identified, predictable solutions (obvious to try)
Known work in one field that would prompt variation in the same or different field
A design need or market pressure that would have led to the combination

These rationales are not exhaustive. The key question always remains: would a PHOSITA have been motivated to combine the references and have had a reasonable expectation of success in doing so?

How Multi-Reference Combinations Are Built?

Building a valid obviousness invalidity combination is not simply about finding two references that together disclose every claim element. There is a structured methodology that practitioners follow to make the combination legally defensible and persuasive.

Step 1: Map Each Claim Element to the Prior Art

The first step is a rigorous claim-by-claim analysis. Every limitation of the challenged claim must be accounted for across the combination. A primary reference typically provides the structural or functional backbone of the invention, while secondary references fill in the missing gaps.

Step 2: Identify a Lead or Primary Reference

The primary reference should be the closest prior art. It should share the same field of endeavor or address the same problem as the claimed invention. Examiners and challengers select a primary reference that discloses the most limitations because this anchor sets the context for why a PHOSITA would look to other references at all.

Step 3: Select Secondary References With a Logical Connection

Secondary references must be relevant and logically connected to the primary. A secondary reference drawn from a completely unrelated field weakens the combination unless a clear motivation to look there can be established. Courts and examiners examine whether the secondary reference solves the same problem or addresses the same technical challenge.

Step 4: Articulate the Motivation to Combine

This is the most critical and most frequently contested part of obviousness invalidity combinations. The motivation to combine must be explicit and grounded in:

The prior art itself (express teachings, suggestions, or examples)
The nature of the problem being solved
The knowledge and common sense of a PHOSITA
General principles recognized in the field at the time of the invention

Post-KSR, conclusory statements are not enough. The motivation must be articulated with specificity, explaining why and how a PHOSITA would have combined the references, not merely that they could have.

Step 5: Establish a Reasonable Expectation of Success

Even with motivation, the combination fails if a PHOSITA would not have reasonably expected the combination to work. This prong is especially important in unpredictable arts like biotechnology, pharmaceuticals, and chemistry, where combining known elements does not always yield predictable results.

Common Mistakes in Multi-Reference Obviousness Arguments

Even experienced practitioners stumble when constructing or responding to obviousness invalidity combinations. Awareness of these common errors can sharpen your arguments on either side of the dispute.

Hindsight reconstruction: Using the claims as a roadmap to cherry-pick references is the most frequently criticized flaw. The combination must be built from the perspective of a PHOSITA at the time of the invention, without knowledge of what was ultimately claimed.
Ignoring teaching away: If a primary or secondary reference explicitly discourages the proposed combination or suggests it would not work, that teaching away undermines the combination.
Vague motivation statements: Saying a combination is “obvious to try” without identifying a finite number of known options or a reasonable expectation of success is legally insufficient after KSR.
Mischaracterizing the PHOSITA’s skill level: Setting the skill level too high or too low skews the entire analysis. The skill level must be grounded in the actual state of the art.
Failing to address objective indicia: Secondary considerations like commercial success, long-felt but unresolved need, failure of others, and industry praise are powerful rebuttal tools that examiners and courts are required to weigh.

Responding to and Overcoming Obviousness Invalidity Combinations

When you receive a multi-reference obviousness rejection, a structured response is essential.

Amendment Strategy: Consider narrowing the claims to introduce limitations not disclosed or suggested by the combination. Adding a specific structural feature, a numeric range, or a functional limitation can distinguish the claims from the assembled prior art.

Argument Strategy: Attack the combination on its weakest point. Challenge the motivation to combine by pointing to differences in the problems addressed, differences in the technical fields, or the absence of any express or implied suggestion in the references to combine them in the proposed manner. If a reference teaches away from the combination, highlight it prominently.

Evidence Strategy: Submit a well-crafted declaration under 37 C.F.R. 1.132 from an expert who can speak to the PHOSITA’s perspective. Declarations addressing why the combination would not have been made, why a PHOSITA would not have had a reasonable expectation of success, or that establish strong secondary considerations can shift the analysis decisively.

Why Obviousness Invalidity Combinations Matter in Litigation?

In inter partes review (IPR) proceedings before the Patent Trial and Appeal Board (PTAB), obviousness invalidity combinations are the dominant weapon used to invalidate issued patents. Statistics consistently show that the majority of IPR petitions rely on obviousness grounds rather than anticipation, precisely because finding a single reference that discloses every element of a well-drafted claim is rare.

For patent owners, understanding how these combinations are structured means being better prepared to draft claims that are harder to combine against, to identify the weak links in a petitioner’s combination, and to marshall the strongest available evidence in response.

For challengers, mastering the art of building airtight obviousness invalidity combinations means selecting the right primary reference, providing a clearly articulated and well-supported motivation to combine, and preemptively addressing foreseeable counterarguments in the petition itself.

Final Thoughts

Obviousness rejections built on multi-reference combinations are among the most nuanced and consequential issues in patent law. Whether you are prosecuting a patent application, defending an issued patent in an IPR, or challenging a competitor’s patent in litigation, the quality of your obviousness invalidity combinations analysis often determines the outcome. Master the legal standards, structure your combinations methodically, avoid the common pitfalls, and always evaluate the case through the eyes of a PHOSITA standing at the priority date, not in hindsight. That discipline is what separates persuasive, winning arguments from weak rejections that collapse under scrutiny.

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