If a claim is amended during Opposition proceedings before the European Patent Office, can it be scrutinised to check that its meaning is clear?  If so, are there any limits to the extent of this scrutiny, or to the types of amendments which can be examined for clarity?

These questions were the theme underlying the issues referred to the EPO’s Enlarged Board of Appeal in case G 3/14.  On 24 March 2015 the Enlarged Board issued its decision, which can be read here.  At over 90 pages in length, the decision is not the easiest to digest, and contains a number of aspects which are likely to provoke further discussion.  Broadly speaking, however, the decision confirms that amendments based on features present in the claims as originally granted cannot generally be re-examined for clarity during Opposition proceedings, even where those features are arguably unclear.

This news may disappoint opponents hoping that an alleged lack of clarity could de facto become a wide-ranging ground for invalidating a European patent, while patentees may welcome the certainty that a claim feature which has been found to be clear during examination of the patent application cannot subsequently be refused as being unclear during Opposition proceedings.  However, features which are newly-introduced to the claims – i.e. features based on the description or drawings which were not present in the originally-granted claims – are not subject to the same restriction, so opponents and patentees alike should keep a close eye out for any arguable lack of clarity in such features.  Parties to Opposition proceedings should also bear in mind that while a lack of clarity is not a ground of opposition as such, clarity can still be relevant in opposition proceedings to the extent that the effect of a prior art document may depend on the interpretation of an unclear claim.

Overall, therefore, while the Enlarged Board’s decision in G 3/14 may not bring lack of clarity into play in Opposition proceedings to the extent opponents may have liked (and patentees feared), neither does it provide a blanket defence against allegations of lack of clarity under all circumstances.  


Under Article 84 of the European Patent Convention, the claims of a patent application must be clear.  The EPO can refuse to grant a patent if it considers this requirement not to be met.  However, according to Article 100 EPC, third parties cannot use an allegation of lack of clarity as a ground for opposing a European patent at the EPO after it has granted.

If  a patent is amended during Opposition proceedings, the Opposition Division must, under Article 101(3) EPC, determine whether the amended claims “meet the requirements” of the EPC.  This raises the question of whether the clarity of amended claims should be examined in opposition proceedings, as clarity is a requirement of the EPC under Article 84, even though a lack of clarity cannot be raised as a ground of opposition.  If clarity is to be examined, further questions arise: should only the amended feature be examined, or should the claim as a whole be re-examined, including unamended features which were in the claim in its originally-granted form?  Should claims be re-examined which are themselves unamended, if they are present in a claim set having an amended claim?

These questions became relevant in Technical Board of Appeal case T 373/12, in which the patentee filed an amendment incorporating a feature from a granted dependent claim into a granted independent claim.  The feature was deemed to be unclear, even though the Examining Division had not raised a clarity objection and had allowed the claims to grant with the “unclear” feature present.

The Questions Referred

Noting two competing and contradictory lines of jurisprudence in previous decisions, the Board in T 373/12 referred four questions to the Enlarged Board.  The questions are not repeated here, but can be read in the full text of the decision.  In essence, these aimed to clarify which, if any, types of amendment should be open to examination for clarity; to what extent the claims should be examined, if at all; and what criteria should be used for determining whether examination was necessary in the event that the board ruled that a clarity examination would sometimes, but not always, be necessary during opposition proceedings.

The Enlarged Board’s answer

The Board answered as follows:

“In considering whether, for the purposes of Article 101(3) EPC, a patent as amended meets the requirements of the EPC, the claims of the patent may be examined for compliance with the requirements of Article 84 EPC only when, and then to the extent that the amendment introduces non-compliance with Article 84 EPC.”

At first sight this seems to raise the question of when an amendment may be said to “introduce” non-compliance with Article 84, i.e. a lack of clarity.  However, the Enlarged Board gave a number of examples in the Decision which consider several types of claim amendments.

The Enlarged Board’s reasoning

The Enlarged Board held that Article 101(3) EPC could not be read as allowing complete re-examination of the entirety of the amended patent for compliance with Article 84 EPC.  The object and purpose of Article 101(3) were not “to open up the patent to a complete re-examination”, and it would be unreasonable if the deletion or amendment of a claim re-opened other, un-amended, claims to examination for clarity. 

In the Board’s view, allowing a wide-ranging re-examination for clarity would in effect make Article 84 EPC a ground for opposition, contrary to the clearly expressed intent of the legislator.  This conclusion was supported by the Board’s review of thetravaux préparatoires for both the original EPC 1973 and the EPC 2000 revision, which showed that “whenever the question has been raised, the legislator has rejected any suggestion that the requirements of Article 84 EPC should be considered as a ground for opposition”.

Types of claim amendments

Having regard to the above principles, the Enlarged Board addressed the following types of claim amendments:

“Type A(i)” amendments: Cases where a dependent claim contains within it alternative embodiments (perhaps with one or more of them being preferred), one of which is then combined with its independent claim.

The Enlarged Board gave the following example, using the term “substantial” as an unclear feature:

Granted claims:

  1. A product comprising X.
  2. A product according to claim 1, comprising also a substantial amount of either Y or [preferably] Z.

Amended claim:

  1. A product comprising X and also a substantial amount of Z.

“Type A(ii)” amendments: Cases where a feature is introduced into an independent claim from a dependent claim, where the introduced feature was previously connected with other features of that dependent claim but has been disconnected from those features when incorporated into the independent claim.

Unhelpfully, no example of such an amendment was given.

“Type B” amendments: Cases involving a literal insertion of a complete dependent claim (or claims) as granted into an independent claim.  The Enlarged Board gave the following example, again using the term “substantial” as an unclear feature:

Granted claims:

  1. A product comprising X.
  2. A product according to claim 1 wherein the amount of X comprised in the product is substantial.

Amended claim:

  1. A product comprising a substantial amount of X.

The Board also envisaged various other types of amendments such as:

  • the deletion of an entire independent claim (usually with its dependent claims); 
  • deletion of some, but not all, dependent claims, leaving the independent claims untouched;
  • deletion of wording from a claim, narrowing its scope but leaving a pre-existing unclear feature intact;
  • deletion of optional features from a claim, leaving all essential features present.

These additional amendments were not specifically addressed, as the Board considered that any answers applicable to “Type A” or “Type B” amendments should also apply to these other amendments.


The Enlarged Board concluded that Type A(i) and Type B amendments, as well as amendments involving the deletion of wording from a claim leaving intact a pre-existing lack of clarity, should be considered closed to renewed examination on grounds of clarity. In doing so, the Board noted that “it is not optimal that there may be granted claims, even after amendment, which do not comply with Article 84 EPC but it cannot be ignored that the legislator has deliberately chosen not to make Article 84 EPC a ground for opposition.”

For Type A(ii) amendments the Board concluded that “it has never been doubted that where an alleged lack of compliance is introduced by such an amendment, the claim may be examined for such compliance. However, where the alleged lack of compliance has not been introduced by the amendment, such cases are in substance no different to Type B.”  For this type of amendment it therefore seems that a careful assessment will have to be made on a case-by-case basis as to whether or not the removal of the feature from its original context “introduces” a lack of clarity.  Bearing in mind that this type of amendment can in many cases give rise to an “added matter” objection under Article 123 EPC, patent proprietors should exercise caution when considering such an amendment.