The related concepts of “toxic priority” and “poisonous divisionals™” have caused a great deal of recent debate. The main issue underlying these concepts concerns partial (and multiple) priority rights for a claimed invention. These rights, however, are unclear following decisions by the Technical Boards of Appeal at the European Patent Office (EPO), which have differed in their interpretation of the law. Newly published decisions which relate to the issue of partial and multiple priority rights are therefore of great interest. T 571/10 is one such recent decision, which has expanded upon the issue of entitlement to partial priority rights and is further discussed here.

The Right of Priority

The right of priority was originally intended to overcome the practical problems faced by patentees in securing patent protection in a number of different countries.  In the absence of a priority period, a prospective patentee would have to co-ordinate all of its patent applications to ensure that they were filed simultaneously; otherwise there would be a risk that, after the original application had been filed in the prospective patentee’s home country, later applications filed in other countries would be refused on the ground that the claimed invention lacked novelty.

A solution was provided in the Paris Convention for the Protection of Industrial Property 1883.  The solution was to treat the original application as fixing the “priority date” for subsequent applications, provided those subsequent applications were made within six months of the original application (later extended to 12 months).  Under the Paris Convention, subsequent applications that are filed within this 12-month period may therefore claim the earlier priority date as their effective filing date (provided certain other conditions are met).  This is important for the patentability of the claimed invention, which will consequently be assessed as of the priority date and not the actual date of filing the subsequent application.

The EPO has adopted its own legal provisions regarding priority, which fit within the provisions of the Paris Convention.  The rules for claiming priority in a European patent application are defined in the European Patent Convention (EPC).

Partial & Multiple Priority Rights

For a European patent (application) to qualify for a right of priority, certain requirements must be met and formalities complied with.  One such requirement is that the application must be filed in respect of the same invention as the earlier application.  Partial and multiple priority rights therefore arise when different elements of the later-claimed invention are disclosed in different (earlier) applications.

To illustrate this by example, a partial priority right will arise when a first application discloses element X and a subsequent application, filed within 12 months of the first application, discloses element X and also a new element, Y.  Claims directed to X in the subsequent application will take the priority date of the first application (because X is the same invention as disclosed in the first application).  For claims directed to Y, however, the date of filing of the subsequent application will apply (because Y is a different invention to that disclosed in the first application).  The subsequent application thus enjoys a partial priority right.

With multiple priorities, the priority of two or more previous applications is claimed.  For example, if application A is filed on 1.1.14 disclosing element X and application B is filed on 1.6.14 disclosing element Y, a subsequent application, C, filed within 12 months of A, will enjoy a first priority right as of 1.1.14 for claims directed to X and a second priority right as of 1.6.14 for claims directed to Y.  Application C is thus said to enjoy multiple priority rights (i.e. a first priority right from A and a second priority right from B).

“Toxic Priority” & “Poisonous Divisionals™”

“Toxic priority” is a term coined for when a priority document becomes novelty-destroying prior art for a subsequent priority-claiming application.  According to some, this can occur when the subsequent application is not entitled to claim priority from the earlier application because it relates to a different invention, and the earlier application is such that the disclosed invention destroys the novelty of that claimed in the subsequent application.  A hypothetical example would be where a first European application discloses only a specific species (e.g. copper) and a subsequent priority-claiming European application claims the broader genus (e.g. any metal).

Similarly, “poisonous divisionals™” relate to a suggested scenario in which a divisional application becomes novelty-destroying prior art for its own parent application.  A divisional application is an application that has been divided from an original (parent) application.  Parent and divisional applications under the EPC have traditionally been awarded the same effective filing date, this being the priority date, or if no priority is claimed, the date of filing of the parent application.  However, a more recent hypothesis is that, if a divisional application is considered entitled to priority (because its claims relate to the same invention as disclosed in the priority document), but the parent application is not (because its claims relate to a different invention), the divisional application will have the earlier effective filing date and, as such, can become novelty-destroying prior art for the parent.

Guidance from the Enlarged Board of Appeal at the EPO

The meaning of “the same invention” under the EPC was considered by the Enlarged Board of Appeal at the EPO in opinion G 2/98.  When formulating its opinion in this regard, the Enlarged Board looked at the issue of multiple priorities, particularly when applied to a single claim.

That multiple priorities may be claimed for any one claim in a European patent application is provided for in Article 88(2) EPC.  Based upon historical documentation related to the EPC and expressing its underlying legislative intent (including the “FICPI Memorandum”), the Enlarged Board considered Article 88(2) EPC to mean that, for a claim directed to feature A or B (feature B being for use as an alternative to feature A), the priority date of each feature may be separate (i.e. the claim can enjoy a first priority for its part A (based upon the earlier application in which feature A was disclosed) and a second priority for its part B (based upon another earlier application in which feature B was disclosed).  The Enlarged Board also considered the provision to mean that, if the claim were directed to feature C, and feature C were in the form of a generic term, formula or otherwise that encompassed the alternative features A and B, then this claim would still be entitled to the aforementioned multiple priorities (based on A and B) “provided that it gives rise to the claiming of a limited number of clearly defined alternative subject-matters”. 

It is this latter condition that has been interpreted differently by the Technical Boards of Appeal at the EPO in subsequent decisions, with one such interpretation giving rise to the concepts of “toxic priority” and “poisonous divisionals™”.

Interpretation by the Technical Boards of Appeal at the EPO

The older, but more common, interpretation of the above condition has been very strict.  For instance, T 1877/08 dealt with a situation in which the earliest priority document listed three chemicals for use as a refrigerant mixture, each with a range of disclosed concentrations.  The claims of the priority-claiming patent listed the same three chemicals and similar, but not identical, concentrations; for example, the priority document disclosed chlorodifluoromethane in a concentration of 30 to 55%, whereas the patent claimed chlorodifluoromethane in a concentration of 30 to 65%.  The Patentee felt that it was entitled to the earliest priority date for at least the overlapping portion, but the Board concluded that “the claimed amounts represent a continuum of a numerical range of values which does not correspond to distinctive alternative embodiments”.  As the Board could not identify any separable elements in the claim, it concluded that the claim as a whole was not entitled to the earliest priority right.  A similar approach was also taken in decisions T 476/09, T 1443/05 and T1127/00. 

It is under this strict interpretation of the condition referred to in G 2/98 that the concepts of “toxic priority” and “poisonous divisionals™” have arisen.  The first concept occurs when the priority claim falls and the priority document becomes available prior art that takes away the novelty of the invention claimed (in a single claim) in the later application.  The second concept occurs when only the parent loses its priority right and the divisional then becomes novelty-destroying prior art for the parent in a similar manner.

However, in a more recent decision, T 1222/11, the Board expressly diverged from the approach taken in T 1877/08, T 476/09, T 1443/05 and T1127/00.  In this decision, the Board felt that it was sufficient, for the purposes of claiming multiple priorities, to be able to “conceptually identify” the aforementioned “limited number of clearly defined alternative subject-matters in the claim”.  Under this interpretation it is therefore acceptable to visualise a broad (generic) claim as a set of theoretical alternatives, and assign them different priorities, without the theoretical alternatives being explicitly stated in the specification.  One example used to highlight this point was that of a first priority document disclosing a range of 15-20 oC, a second priority document disclosing a range of 10-25 oC and a patent application claiming a range of 10-25 oC.  By comparing the claimed subject matter with the disclosure of the priority documents, the theoretical alternatives covered by the claim were identified as the ranges, 10-15oC, 15-20 oC and 20-25 oC.  The range of 15-20 oC was seen as entitled to the earliest priority date, whilst the two outside ranges were seen as entitled to only the second priority date; these ranges could therefore enjoy different priority rights despite being part of one broad range in a single claim.  The Board explicitly acknowledged that its interpretation of the condition referred to in G 2/98 was different from that taken by the other Technical Boards in T 1877/08, T 0476/09, T 1443/05 and T 1127/00.  However, to support its interpretation, the Board highlighted that the Enlarged Board had referred to the “FICPI Memorandum” in G 2/98, which expressed the legislative intent underlying Article 88 (2) EPC.  This memorandum outlined a clear intention with which T 1222/11 was in line; the temperature example discussed above was also taken from the memorandum.  The same Board had also taken a parallel approach in an earlier case, T 665/00.

Under this, more lenient, interpretation of the condition referred to in G 2/98, the concepts of “toxic priority” and “poisonous divisionals™” cannot exist.

Recently published decision T 571/10 is based on the same approach as T 1222/11 and T 665/00.  It therefore helps to reaffirm this interpretation of the law, but it should perhaps be noted that all three decisions have been made by the same Board (3.3.07).

T 571/10 concerned a European patent application relating to a pharmaceutical composition for use as an enzyme inhibitor.  The application claimed priority from a document disclosing a composition including a calcium salt of the active ingredient and a tribasic phosphate salt.  However, the application itself claimed “a pharmaceutically acceptable salt” of the active ingredient (instead of a calcium salt) and an “inorganic salt” (instead of a tribasic phosphate salt).  Thus the application claimed broader categories which included, but did not identify, the more specific disclosures of the priority document.  Like the earlier cases discussed above, the question of priority had a real effect on the allowability of the application in question due to a potentially citeable and novelty-destroying prior art document.

The Board noted that the generic terms, “pharmaceutically acceptable salt” and “inorganic salt”, as used in the claim in question, could both be written as lists of distinct alternatives and that, for the purpose of determining partial priority, they should indeed be visualised in this way.  To do this, the Board compared the claimed subject matter with the disclosure of the priority document and theoretically split the claim into two alternatives: (a) a calcium salt and a tribasic phosphate salt (disclosed in the priority document); and (b) a pharmaceutically acceptable salt and an inorganic salt other than a calcium salt and a tribasic phosphate salt (making up the rest of the claim).  The presence of the disclaimer in (b) was simply so that this option covered all identifiable alternatives not listed in (a).  The Board decided that, as (a) was clearly disclosed in the priority document, this part of the claim enjoyed the earlier priority right.  However, as (b) was not disclosed in the priority document, all alternatives described by (b) as encompassed by the claim did not enjoy a right of priority.  Splitting the priority rights in this manner meant that the potentially conflicting document did not form novelty-destroying prior art for any of the claimed subject matter.  In this regard, part (a) of the claim was entitled to claim priority and so the potentially conflicting document did not form part of the state of the art (i.e. it was not available for the assessment of novelty for part (a) of the claim).  Part (b) of the claim was not entitled to claim priority and so the conflicting document formed part of the state of the art for this part of the claim.  However, as above, the conflicting document only disclosed (a), which was different to (b); it consequently did not destroy the novelty of part (b) of the claim.

T 571/10 therefore reaffirms the notion that partial and multiple priorities can be applied in such a way that “toxic priority” and “poisonous divisionals™” cannot exist.  Indeed, the application in question claimed a broad category that nevertheless enjoyed a partial priority for the narrow selection disclosed in the priority document.  This line of reasoning precludes the possibility for “toxic priority” and “poisonous divisionals™” to exist, as an application can enjoy a right of priority for any features disclosed in the priority document, yet any newer features, that are not disclosed in the priority document but encompassed by the claims, cannot be anticipated by it.

Further Guidance from the Enlarged Board

So what can applicants for European patents learn from this? 

The reasoning used in T 571/10 and its earlier counterparts (T 1222/11 and T 665/00) seems robust and well supported by the historical documents that show the original intent behind Article 88 (2) EPC, and so it may well become the confirmed approach to partial and multiple priorities in the future.  Whether that happens or not remains to be seen, but clarification is now due to come from the Enlarged Board of Appeal at the EPO. 

Indeed, in view of the fact that Technical Boards of Appeal have reached different conclusions on the same question of how to interpret the condition referred to in G 2/98, the matter has now been referred to the Enlarged Board. 

The referral was made by a Technical Board following recent appeal proceedings (in T 557/13), in view of the clear inconsistency between the earlier decisions, T 1222/11 and T 1877/08 (amongst others).  T 557/13 related to a patent that had been revoked in opposition proceedings at the EPO, based upon claims that were deemed not entitled to their priority claim (following T 1877/08).  As a result the patent, being a divisional application, was held invalid in light of its parent case, this being deemed entitled to the priority claim.  More a case of “poisonous parent”, than “poisonous divisional™”, therefore!

The exact questions to be answered by the Enlarged Board have not yet been determined, but they will presumably rationalise how partial and multiple priorities should be applied.  An opinion or decision from the Enlarged Board in this regard should remove legal uncertainty and thus clarify the validity of priority-claiming European patents and applications.  Knowing when partial and multiple priorities are available would enable a better understanding of whether priority documents can ever be toxic or divisional applications poisonous.

Naturally we shall keep you informed of any developments.