European Patent Attorney Deep Dive: From Two-Part Claims to Unitary Patent Strategy
CNIPA.AI Team
Tech Blog
The European Patent Office (EPO) operates one of the world's most rigorous and distinctive patent examination systems. For practitioners accustomed to USPTO or CNIPA procedures, switching to EPO practice requires a systematic knowledge rebuild—not merely a format adjustment, but a fundamental shift in examination logic. This guide systematically addresses seven core EPO practice areas from a practitioner's perspective, with direct comparisons to US/JP/CN practice.
Target readers: Patent attorneys handling EP national phase from PCT; litigation attorneys managing EPO Office Actions; IP directors designing multi-jurisdictional patent strategies.
1. Two-Part Claim Form: The Core Format Requirement of EPC Rule 43(1)
1.1 Structural Mandatory Nature
The EPO requires independent claims to follow the "two-part form" structure (EPC Rule 43(1)(a)), consisting of two clearly delineated parts:
- Preamble: Describes the subject matter of the invention and the technical features it shares with the closest prior art.
- Characterising Portion: Introduced by "characterised in that" (English), "dadurch gekennzeichnet, daß" (German), or "caractérisé en ce que" (French), setting out the technical features that distinguish the invention from the closest prior art.
A typical structure looks like this:
A wireless communication device comprising:
a processor configured to receive data packets; and
a memory storing program instructions;
characterised in that the processor is further configured to apply
a differential privacy mechanism to the data packets before transmission,
wherein the differential privacy mechanism uses a Laplacian noise parameter
calibrated to a sensitivity threshold of the transmitted dataset.
Key difference from US/JP: USPTO claims do not require a two-part form; attorneys typically use "comprising" to introduce all features. Japanese patent claims use "ことを特徴とする" (characterizing clause), also a single-block structure. The EPO two-part form requires the drafter to identify the "closest prior art (D1)" before drafting and incorporate D1's known features into the preamble.
1.2 Strategy for Dividing Preamble and Characterising Portion
In practice, the preamble/characterising division is an art rather than a mechanical exercise:
| Scenario | Recommended Strategy |
|---|---|
| D1 is a single document with clear distinguishing features | Place all D1 teachings in preamble; characterising portion contains only distinguishing features |
| Multiple prior art documents together constitute "closest prior art" | Select the technically closest single document as D1; others serve as background |
| Invention is entirely novel (no obvious D1) | Preamble may describe only the claim category (e.g., "A method for..."); characterising portion covers all substantive features |
| Product + method combination | Each claim type has its own two-part division; mixing is generally not permitted |
Critical practice note: EPO examiners will re-divide preamble/characterising portions. If the drafter places actual distinguishing features in the preamble, the examiner may move them to the characterising portion in the first OA, thereby narrowing the scope. Conservative drafting is advisable—only place features explicitly disclosed in D1 in the preamble.
1.3 Exceptions to the Two-Part Form
EPC Rule 43(1) itself allows alternative formats when the two-part form is "not appropriate" (Rule 43(1)(b)). In practice, consider this for:
- Chemical compound claims: Structural features often cannot be distinguished from prior art using the two-part form
- Use claims: Such as "Use of compound X for treating disease Y"
- Novelty residing solely in use: Markush structure claims where the compounds are known and the use is novel
2. Problem-Solution Approach (PSA)
2.1 EPO's Unique Methodology
PSA is the EPO's standard methodology for assessing inventive step under EPC Art. 56, with no formal equivalent at USPTO, JPO, or CNIPA. Practitioners unfamiliar with PSA's operational logic will be at a severe disadvantage when responding to EPO Office Actions.
PSA follows three steps:
Step 1: Identify the Closest Prior Art (D1) D1 is typically: the single document most closely related to the invention's technical field and representing the best starting point for achieving the invention's purpose. Selection of D1 significantly affects the trajectory of examination.
Step 2: Determine the Objective Technical Problem (OTP) The OTP is not the technical problem stated by the applicant in the description, but is redefined by the examiner based on the technical effect actually achieved by the distinguishing features over D1. A typical OTP formulation: "How to improve the device of D1 to achieve effect X?"
Step 3: Assess Obviousness The examiner determines: would the prior art (D1 or D1+D2+...) teach, suggest, or prompt a person skilled in the art (POSITA) to adopt the distinguishing features to solve the OTP?
2.2 PSA-Oriented Description Drafting Strategy
Understanding PSA, practitioners should adopt the following strategies when drafting the description:
| Description Section | PSA-Oriented Key Points |
|---|---|
| Background Art | Clearly describe D1's structure and limitations; cite D1 by publication number |
| Disclosure of Invention | Explicitly state "distinguishing features over D1" and the "technical effects" they produce; avoid describing only the technical solution without mentioning technical effects |
| Embodiments | Each embodiment should correspond to at least one distinguishing feature; more embodiments means higher sufficiency |
| Claims | Independent claims contain only essential technical features; dependent claims cover preferred embodiments (providing fallback positions for prosecution) |
Practice note: EPO examiners frequently downgrade the applicant's stated "technical problem" to "providing an alternative," making it easier to combine D2 against the invention. The counterstrategy is to quantify technical effects in the description (e.g., "improving efficiency by 30%"), preventing easy downgrading of the technical problem.
2.3 EPO vs USPTO: Two Inventive Step Frameworks Compared
| Dimension | EPO (PSA) | USPTO (TSM/Graham Analysis) |
|---|---|---|
| Starting point determination | Must identify a single D1 | No "closest prior art" requirement |
| Problem definition | Examiner redefines OTP | Applicant's stated problem carries more weight |
| Objective/subjective orientation | Objective (OTP based on actual distinguishing features) | More consideration of applicant's subjective intent |
| Hindsight protection | PSA framework provides some protection | Obviousness analysis more susceptible to hindsight |
| Motivation to combine | "Prompt" standard, stricter | "Motivation + reasonable expectation of success," more flexible |
3. Unity of Invention (EPC Rule 44)
3.1 One Independent Claim Per Category Principle
EPC Rule 43(2) provides that the same category normally allows only one independent claim, with exceptions including:
- Mutually related products (e.g., plug + socket)
- Different uses of the same product
- Alternative solutions to the same technical problem
Key difference from USPTO: USPTO permits multiple independent method and apparatus claims in a single claim set, provided the attorney pays additional claim fees (>3 independent claims incur $500/claim surcharge). EPO instead imposes a format-level "one per category" requirement.
Practical approach: EP applications are typically drafted with "Method + Apparatus" dual independent claims—different categories, compliant with Rule 43(2). Adding a "System" independent claim requires evaluating whether it differs from "Apparatus" as a category (usually possible).
3.2 Responding to Unity Objections
The EPO Search Report (EESR) may find lack of unity and search only the first invention. Response strategies:
- Voluntary limitation: Narrow the main claim to the first invention's scope; dependent claims cover the other inventions
- Divisional application: File divisional applications (EPC Rule 36) for other inventions
- Challenge the finding: If the unity objection is considered incorrect, contest it in the OA response
4. Sufficiency of Disclosure (Art. 83 EPC) and Added Matter (Art. 123(2) EPC)
4.1 Art. 83 Sufficiency Requirement
EPC Art. 83 requires the description to disclose the invention "in a manner sufficiently clear and complete for it to be carried out by a person skilled in the art."
EPO enforces Art. 83 more rigorously than USPTO § 112(a), particularly in:
| Technical Field | Art. 83 High-Risk Areas |
|---|---|
| Biotechnology | Strains and cell lines without public deposit may not sufficiently support broad claims |
| Chemical synthesis | Broad Markush structures with only a few examples may face insufficiency challenges |
| AI/Machine learning | Describing only functional outcomes ("neural network achieves X") without implementation details may be insufficient |
| Functional claiming | Functional features in claims must have structural support in the description |
Practice advice: For each technical feature in independent claims, there should be at least one corresponding embodiment in the description. AI/software inventions should include at least one complete implementation description (architecture diagram + step-by-step description).
4.2 Art. 123(2) Added Matter Prohibition
Art. 123(2) prohibits amendments after filing from introducing "subject-matter which extends beyond the content of the application as filed."
This is one of the most troublesome "traps" in EP prosecution:
| Amendment Type | Art. 123(2) Risk |
|---|---|
| Incorporating dependent claim features into independent claim | Low risk (generally supported) |
| Adding specific numerical values not in the original filing | High risk |
| Combining features from multiple embodiments ("cherry-picking") | Medium-high risk |
| Deleting intermediate-breadth claims | Requires care; may trigger Art. 123(3) |
Prevention strategies at the drafting stage:
- Include explicit "alternative embodiment" descriptions for each claim feature
- For potential numerical ranges, cover endpoints in the description (e.g., "between 10 and 50, preferably 20")
- Particularly note: cannot create feature combinations that did not appear as such in the original application
5. Reference Signs (EPC Rule 43(7))
5.1 Mandatory Requirement
EPC Rule 43(7) provides: where the description contains drawings, technical features mentioned in the claims shall be followed by reference signs placed in parentheses—without limiting the scope of the claims.
Format specifications:
- Correct:
a processor (102) configured to receive data packets - Incorrect:
a processor configured to receive data packets (see Fig. 1) - Incorrect: omitting reference signs when the description contains drawings
5.2 Reference Signs in Practice
| Practice Point | Explanation |
|---|---|
| Do method claims need reference signs? | Generally no (method claim features are hard to correlate to drawing numerals), but may be added if steps correspond to figures |
| Same feature across multiple claims | Should use consistent numerals (same technical feature uses the same numeral throughout) |
| Consistency between description and claims | Must be consistent; EPO Form Examination checks for inconsistencies |
| Format of reference signs | Always in parentheses; processor 102 format (without parentheses) is incorrect |
6. No Grace Period and Application Timing
6.1 EPC's Strict Approach
EPC Art. 54 provides that all disclosures before the filing date or priority date (including the applicant's own disclosures) constitute prior art affecting novelty. EPC Art. 55 provides only two very narrow exceptions:
- Obvious abuse: within 6 months
- Display at an official international exhibition: within 6 months
This represents a fundamental difference from USPTO's 12-month grace period (35 U.S.C. § 102(b)(1)).
6.2 Strategic Impact on Multi-Jurisdictional Filing
| Disclosure Act | Impact on EP | Recommended Action |
|---|---|---|
| Academic paper publication | Destroys EP novelty (if published before filing date) | File US provisional or CN application first, claim priority |
| Product sales/demonstration | Destroys EP novelty | Same as above |
| Conference presentation | Destroys EP novelty (even without paper publication) | File before the conference |
| Online disclosure (social media, GitHub) | Destroys EP novelty | Immediately file provisional application |
Practice recommendation: For inventions intended for EP filing, establish a "file before publish" company policy, completing at least one priority application (US provisional or CN priority application) before any disclosure.
7. Multiple Dependent Claims Strategy and Fee Optimization
7.1 EPO's Multiple Dependency Advantage
A key distinction from USPTO: EPO charges no additional fees for multiple dependent claims. USPTO charges approximately $860 per multiple dependent claim (2024 standard), leading US attorneys to avoid multiple dependencies.
EPO fee structure (2026 standard):
- First 15 claims: no additional fees (included in application fee)
- From claim 16 onwards: approximately EUR 280 per claim
EPO multiple dependency strategy: Within the constraint of no more than 15 total claims, strategic use of multiple dependencies (e.g., "The device according to any one of claims 1 to 3, wherein...") can substantially expand actual claim coverage without additional fees.
7.2 Restructuring US Claims for EP Format
When converting a US claim set to EP format, common strategies include:
| US Claim Characteristic | EP Conversion Strategy |
|---|---|
| Multiple parallel independent claims | Consolidate into one independent + multiple dependent claims |
| Avoiding multiple dependencies (to save fees) | Switch to multiple dependencies to reduce total claim count |
| Functional claims (means-plus-function) | Convert to structural description to avoid Art. 83 risk |
| Jepson format | Directly corresponds to EP two-part form; conversion is straightforward |
8. Designation States, Validation States, and Unitary Patent (UPC)
8.1 Geographic Coverage System
EP application geographic coverage involves three tiers:
| Tier | Content | Count |
|---|---|---|
| EPC Contracting States | Core European countries, automatically designated | 39 |
| Extension States | Some non-EPC countries may choose extension | 2 (MA, MD) |
| Validation States | Countries with EPO validation agreements | 6 (TN, KH, GE, LA, EG, IL) |
8.2 Unitary Patent and UPC
On 1 June 2023, the Unified Patent Court (UPC) came into force and the Unitary Patent system launched simultaneously.
Core characteristics of the Unitary Patent:
- Must be requested within 1 month after EPO grants the patent
- Provides uniform protection in approximately 18-25 participating EU member states (as of 2026)
- Single renewal fee (paid centrally, no separate national fees required)
- Unified revocation procedure (a single revocation action affects all participating states)
Decision framework: Unitary Patent vs. Traditional National Validation:
| Consideration | Favors Unitary Patent | Favors Traditional Validation |
|---|---|---|
| Countries needed | Protection in multiple EU countries | Only a few key markets |
| Enforcement risk | Need enforcement in multiple countries | Enforcement only in a few countries |
| Revocation risk | Accept pan-European effect of one action | Can manage risk in isolation by country |
| Annual fee budget | Unitary fee usually lower than validating in all countries | Validating in a few countries costs less |
| Translation requirements | None (after transition period) | Local language translation required for each country |
Practice recommendation: For applicants with substantial commercial interests in 3+ EU countries, the Unitary Patent is generally the more economical choice. For high-infringement-risk industries (pharma, semiconductors), carefully evaluate UPC revocation risk.
9. How CNIPA.AI Assists in the European Patent Process
The difficulty of EP prosecution lies in requiring precise EPC legal knowledge combined with practical experience at every step. Here are specific scenarios where AI tools can add value in EP practice:
Claims Drafting Assistance:
- Auto-generate two-part form compliant with EPC Rule 43(1), including the correct "characterised in that" separator
- Automatically distribute technical features between preamble and characterising portion based on technical description
- Auto-insert Rule 43(7) reference signs
Problem-Solution Analysis:
- Identify potential distinguishing features based on the input technical solution
- Assist in generating Objective Technical Problem (OTP) formulations aligned with PSA logic
- Check whether the description explicitly records the technical effect of each distinguishing feature
Format Compliance Checking:
- Art. 83 embodiment coverage check: verify each independent claim feature has a corresponding description
- Art. 123(2) early warning: flag potential added matter in amendments
- Reference sign consistency verification
These capabilities are assistive tools. Final legal judgments (D1 selection, OTP definition, amendment boundaries) remain the responsibility of qualified European Patent Attorneys (EPA).
Appendix: EPC Key Provisions Quick Reference
| Provision | Subject | Core Content |
|---|---|---|
| EPC Art. 52 | Patentable subject matter | Excludes business methods, mental acts, computer programs ("as such") |
| EPC Art. 54 | Novelty | All disclosures before filing date constitute prior art (no grace period) |
| EPC Art. 55 | Grace period exceptions | Within 6 months of obvious abuse or exhibition disclosure |
| EPC Art. 56 | Inventive step | Assessed using PSA methodology |
| EPC Art. 83 | Sufficiency of disclosure | Description must enable POSITA to carry out the invention |
| EPC Art. 84 | Clarity and support | Claims must be clear, concise, and supported by the description |
| EPC Art. 123(2) | Amendment restriction | Must not introduce subject matter beyond the original application |
| EPC Rule 43(1) | Claim format | Two-part structure (preamble + characterising portion) |
| EPC Rule 43(2) | Multiple independent claims | Normally only one independent claim per category |
| EPC Rule 43(7) | Reference signs | Drawing references must be noted in parentheses in claims |
| EPC Rule 44 | Unity of invention | Claim set must relate to a single inventive concept |
| EPC Rule 47 | Abstract | Maximum 150 words, third person, single paragraph |
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