At first glance, Article 123 of the European Patent Convention might appear straightforward, but it hides a notorious concept, known as ‘the inescapable trap’: if a granted claim involves added matter, there is no way to restore it except by shifting the scope of the patent, which violates the principles of patent law and hence invalidates the patent. The patentee thus actually shoots itself in the foot by doing so. Recent European Patent Office (EPO) practice suggests that there might be another way for patentees to shoot themselves in the foot: through 'poisonous priority'.

Poisonous priorities

Priority is the right of an applicant to claim the filing date of its first application if, within 12 months, it files another application in respect of the same invention. This principle was established under the Paris Convention 1883 in order to help inventors to protect their ideas. However, today EPO practice shows that a priority claim may backfire on the patentee.

So how do priorities become toxic? Commonly, there are further technical developments during the priority year, perhaps even driven by new insights from the search report received during that time. A difficult situation can arise when the later application claims broader subject matter than was originally disclosed in the first application. What happens if the first application discloses features A, B and C, but the subsequent application claims features A, B, C and D? Or if the invention is first a combination of A and B, but it later emerges that a claim based on A alone suffices? EPO Decision G2/98 made clear that for such claims, priority is lost. Any publication during the priority year can be used against the applicant.

So far, so good. But what if the first application is published and still discloses embodiments within the scope of the claim? In that case, a prior right exists under Article 54(3) of the European Patent Convention, destroying the novelty of the subsequently filed claim. This is how priority can be poisonous for the fate of an application.

Toxic divisional attack

One way to avoid such toxic priorities is by not making the priority document available as a prior right document. Even then, however, the applicant may still face a similar toxic issue if it files a divisional application with the subject matter found in the priority document. The claims of this divisional application are entitled to priority, as they relate to the same invention as the priority document; but if the parent application had lost priority due to broader claims, the divisonal application becomes novelty destroying to its parent.  

There is no provision in the European Patent Convention that prohibits such self-collision between parent and divisional, and under EPO case law a ‘toxic divisional’ attack can be based on it. Since Decision T1496/11 set the tone, the use of this controversial weapon during opposition and appeal proceedings has increased, much to the concern of practitioners.

The antidote

So what is the antidote? In G2/98 the EPO Enlarged Board of Appeal tried to provide one by introducing a test for establishing partial priority. If the priority document discloses "a limited number of clearly defined subject matters", these will keep their priority date as part of a claim in a later application, even if they are claimed together with extensions to the subject matter introduced in the later filing, provided that the resulting claim also contains "a limited number of clearly defined alternative subject matters". Hence, such claim will have multiple effective filing dates.

The legislature envisaged allowing partial priority for the following situation: where the priority document discloses feature A and the subsequent application claims feature A or feature B, feature A will enjoy priority and feature B will get the filing date. The legislature also suggested allowing multiple effective filing dates for the situation where a species is disclosed in the priority document and its genus is subsequently claimed, as long as that genus encompasses "a limited number of clearly defined alternatives" (eg, if the priority document discloses "rat" and the subsequent application claims "rodents", "rat" will enjoy priority and the other rodent species (a limited number and arguably clearly defined alternatives) will get the filing date).

But there is a twist – when is a subject matter clearly defined? Must the priority document explicitly spell out the alternative embodiments (eg, mention all of the other rodent species except for rats)? Or is it sufficient that these alternative embodiments may be conceptually identified on the basis of the priority document? In other words, is it sufficient that the skilled person may "directly and unambiguously" derive these alternatives from the priority document?

G2/98 test applied: from broad to narrow to broad again?

Decision T665/00 set out a brave interpretation of G2/98 and set the stage for the discussion on this issue. In that case the priority document disclosed an example in which microspheres were used with a specific mass of 0.04 grams per cubic centimetre (g/cubic centimetre), but the subsequent application claimed microspheres with a specific mass of less than 0.1g/cubic centimetre. Thus, a single point value was used to claim priority for a range which contained an infinite amount of possible values: how limited and clearly defined was that?

Strictly speaking, and according to the G2/98 test, such priority claim was invalid. Consequently, the subsequent application would get the filing date, rendering the priority document toxic as prior art under Article 54(3) of the European Patent Convention. Despite the priority claim in T665/00 being invalid, the board held that the example in the priority document could not be used as an anticipation against the claim in the subsequent application. The board fitted the issue into the convention’s legislative framework by saying that there would have been a valid priority claim only for this exact example. In the context of G2/98, the board reasoned that the ensemble of microspheres less than 0.1g/cubic centimetre was to be seen as a claimed genus – a pool of embodiments out of which only the single point value of the 0.04g/cubic centimetre species would enjoy priority because it was disclosed in (the example of) the priority document. All other microspheres of less than 0.1g/cubic centimetre (not equal to 0.04g/cubic centimetre) would thus be entitled to the filing date. Although this gave rise for some discussion at the time, it appeared to be settled.

Since then, a whole line of case law has been created on this point and the board has appeared divided on the issue. Some Board of Appeal decisions (eg, T1127/00, T1443/05, T1877/08, T0476/09) have followed a narrow interpretation of the G2/98 test, requiring explicit disclosure of alternatives in order to successfully claim partial priority. For example, disclosing "A-B-C-D" is acceptable for claiming all of these embodiments, but disclosing "A to D" will allow priority only for explicit embodiments A and D. Or, in the case of ranges, a range from the priority document (eg, 1-10) will overlap with the subsequently claimed range (eg, 5-15), and it will not be possible to claim priority for the overlapping portion (5-10) because these ranges are continuums of values and thus do not correspond to distinctive alternative embodiments.

More recently, in T1222/11 an appeal board broke with this line of previous case law decisions. It took its own broader approach to assess partial priority, allowing for the subject matter of a claim to be fragmented theoretically into the bits from the priority document and extensions on filing, without even requiring explicit identification of every single embodiment in the priority document (eg, "A to D" will now also allow priority for embodiments A, B, C and D). To establish whether G2/98’s "limited number of clearly defined subject matters" was disclosed in the priority document, the board advocated using the well-known directly and unambiguously derivable test from G3/89, resulting in a more context-driven assessment, rather than an assessment based on the literal text. Decision T571/10 adopted and endorsed this broader approach. So is there a return to the original T665/00 perspective which is more in favour of the patentee? One thing is certain: there is inconsistency in the EPO's jurisprudence.

Clarify the law regarding partial priorities: detoxification?

Faced with the same toxic issues in T557/13, the Technical Board of Appeal turned to the Enlarged Board of Appeal for clarification of the law regarding partial priorities in regard to two issues:

  • When is it available?
  • Is there a threat of toxic divisionals?

These queries were broken down into the following questions which were formally referred to the Enlarged Board of Appeal and were recently published. Some of them address the tests provided in G2/98. Context is needed to understand the meaning of 'limited number of clearly defined subject matters’:

  • Where a claim of a European patent application or patent encompasses alternative subject matters by virtue of one or more generic expressions or otherwise (a 'generic OR claim'), may entitlement to partial priority be refused under the European Patent Convention for that claim in respect of alternative subject matter disclosed (in an enabling manner) for the first time directly, or at least implicitly, and unambiguously in the priority document?
  • If the answer is yes, subject to certain conditions, is the proviso "provided that it gives rise to the claiming of a limited number of clearly defined alternative subject-matters" in Point 6.7 of G 2/98 to be taken as the legal test for assessing entitlement to partial priority for a generic OR claim?
  • If the answer to the second question is yes, how are  'limited number' and 'clearly defined alternative subject matters' to be interpreted and applied?
  • If the answer to the second question is no, how is entitlement to partial priority to be assessed for a generic OR claim?
  • If an affirmative answer is given to the first question, may subject matter disclosed in a parent or divisional application of a European patent application be cited as state of the art under Article 54(3) of the convention against subject matter that is disclosed in the priority document and encompassed as an alternative in a generic OR claim of the European patent application or of the patent granted thereon?

Addressing tension between patent system ideology and patent law fundamentals

Interestingly,the fifth question was not at issue between the parties in T557/13, but was formulated on the initiative of the referring board. This may suggest that the EPO realises that the whole issue touches on the fundaments of the patent system and that the EPO is willing to go the extra mile to ensure more robust legislation.

The fifth question addresses a key area of tension. On one hand, there is the feeling that it would be unfair for an applicant to have its own priority document treated in such way that it loses its subsequent patent, since patents are a reward for an applicant’s inventive effort and this aspect is generally not significantly challenged by toxic priority. In the case of divisionals, the possibility of a toxic attack with a parent seems even more unfair: by definition, divisionals may contain only subject matter disclosed in the parent and they retain the parent’s filing and priority dates. As such, a divisional is in essence a (partial) duplication of the parent, so it would be illogical to allow for one to anticipate the other. On the other hand, these philosophies appear to be incompatible with the existing legal framework, which is set up in such a way that subject-matter priority is a strict literal issue, prior rights have novelty-destroying capability and the fate of a divisional is entirely independent of its parent. The EPO has demonstrated that it is aware of the need to clarify this issue and render the service claimed in its mission statement: "commitment to high-quality and efficient services delivered under the European Patent Convention."

Time will tell whether the EPO Enlarged Board will implement a detox regime to tackle the toxic priorities and divisionals in its proceedings.

Shiri Burema

This article first appeared in IAM magazine. For further information please visit www.iam-magazine.com.