Since a decision of the Enlarged Board of Appeals in 1984, the European Patent Office has permitted a patentee to file an opposition against its own European patent. This has provided a convenient way of effecting a Europe-wide amendment of a patent after grant without becoming enmeshed in national proceedings for post-grant amendment.

In a decision on a patent in the names of Peugeot and Citroen, the Enlarged Board of Appeals concluded that its previous decision authorizing this practice was wrong and reversed that decision. In the new decision, the Board concluded that the whole tenor of the provisions relating to oppositions in the European Patent Convention requires that such proceedings should be inter partes. This does not occur when the patentee opposes itself.

The Board recognized the problems that arise when such reversals occur in view of the general principle that the Enlarged Board of Appeals merely interprets, but does not create, the law so that the law must be regarded as always having been what it is now stated to be. Therefore, the Board stated that its present decision shall have only prospective effect and thus will not apply to self-oppositions filed before the present decision. The Board glossed over the logical inconsistency of its position by stating that in this case the issues involved were procedural rather than substantive, implying that in such cases some flexibility in the application of the general principle is appropriate.