In this article we examine key aspects of the PSA before the EPO. Thereby, we consider recent T decisions.
The problem-solution approach (PSA) is the standard method used by the European Patent Office (EPO) to assess whether an invention is inventive, i.e. not obvious.
The takeaways are based on the EPO´s Case Law Conference 2025 (November 20/21, 2025).
Recent T decisions relating to the PSA:
- T 428/23 – incentive
- T 746/22 – arbitrary modifications
- T 449/23 – burden of proof
T 428/23 of 20.03.2025 – FENCE STRUCTURE (EP 3054066 B1)
Key Question:
Must the motivation to consult a further prior art document come from the closest prior art (CPA)?
The invention:
A fence structure comprising … vertical uprights (3) … characterized in that … (3) are made of COR-TEN steel.
- COR-TEN steel is a weathering steel and is known for its high corrosion resistance
The dispute:
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CPA (D16): A document disclosing a higly similar fence structure with tubular metallic uprights, but not specifying COR-TEN steel
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Distinguishing Feature: The uprights are made of COR-TEN steel
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Objective Technical Problem (OTP): How to improve the corrosion resistance of the fence known from D16?
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Core question: Had it been obvious to solve this problem by using COR-TEN steel?
Proprietor’s argument: No reason to change
The proprietor argued that the invention was not obvious for two main reasons:
Lack of an incentive in the CPA:
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D16 already disclosed materials with good corrosion resistance
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The document itself provided no hint or incentive for the skilled person to look for a different material
Alleged Technical Prejudice:
- Citing a Wikipedia article (D32), a skilled person would have been dissuaded from using COR-TEN steel due to a known prejudice against its use in salty environments or where water might accumulate
Board´s decision: Incentive from second document
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The invention is obvious
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Grounds for “Incentive”:
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It is a “conceptual error” to require that the closest prior art must provide an incentive
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The motivation to modify usually comes from the “secondary teaching” when solving OTP
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Grounds for “Prejudice”:
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The alleged prejudice based on D32 was not general, but specific to large-scale buildings in construction. This limited context would not dissuade a skilled person from using the material for a simple fence.
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Key Takeaway: The “would” in the could-would approach is satisfied if the skilled person, faced with a problem, would have looked to known solutions to solve it. The motivation does not need to be signposted in the starting document.
T 746/22 of 06.02.2025 – OPTICAL SYSTEMS FOR MULTI-SENSOR ENDOSCOPES (EP 2635932)
The invention:
An optical system for a tip section of a multi-sensor endoscope …, wherein the mathematical condition f(first rear positive lens) <= 1.8f is given relating to the focal lengths of the lenses.
The dispute:
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CPA (D4): a highly similar five-lens system, which does not meet the claimed mathematical condition
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Distinguishing Feature: The relationship f3 ≤ 1.8f
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Core Question: Does modifying the prior art to meet this specific mathematical condition involve an inventive step?
Board´s analysis: No effect, no problem
Step 1: What is the Technical Effect?
- The mathematical condition was just an abstract relationship not leading to any relevant technical effect
Step 2: What is the OTP?
- Since there is no technical effect associated with the distinguishing feature, no OTP can be formulated
Board´s decision: No problem, no inventive step
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The invention is an arbitrary modification of the prior art and therefore lacks an inventive step
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Grounds:
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If a distinguishing feature does not credibly solve a technical problem, no inventive step can be based on it ( T 176/97)
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The proprietor’s argument of “no incentive to modify” was dismissed; the question of motivation is irrelevant when a modification is arbitrary and non-functional
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Key Takeaway: For a feature to contribute to inventive step, it must produce a credible technical effect.
T 449/23 of 12.12.2024 – METHOD FOR PREPARING CATIONIC ELECTRODEPOSITION COATING COMPOSITION (EP 3354701)
The dispute:
When a proprietor relies on an improved technical effect to argue for inventive step, who has the burden of proving that this effect exists?
Boards’s decision: The burden of proof lies with the proprietor
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“Legal Burden” (duty to persuade) vs. “Evidentiary Burden” (duty to produce evidence):
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Legal Burden does not shift:
The opponent must present a prima facie case for obviousness.
To counter this with an alleged effect, the proprietor bears the legal burden of proving that the effect is achieved.
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Evidentiary Burden can shift:
If the proprietor provides strong, convincing evidence for an effect, the onus then shifts to the opponent to rebut it with counter-evidence or substantiated doubts
Outcome: The board formulated a less ambitious OTP, i.e. the provision of an alternative, and found that the claims are obvious.
Core Teaching: A mere assertion of an advantage in the patent specification is not a proof. The prorietor must be able to prove it with credible, comparative evidence.
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