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In opinion G 2/98 (OJ 2001, 413) the Enlarged Board of Appeal addressed the whole concept of "the same invention" in Art. 87(1) EPC 1973. (The relevant provisions were not amended in the EPC 2000 and the principles set out below continue to apply.) In the years preceding the opinion of the Enlarged Board in this case, the boards applied different yardsticks to assess identity of invention between a previous and subsequent application. One was to check whether all the features of the invention claimed in the European patent application were disclosed in the priority document ("novelty test"). In T 311/93 and T 77/97 in particular, boards looking at the validity of priority claims continued to apply the criterion of at least implicit disclosure used for the disclosure test under Art. 123(2) EPC 1973. Other decisions however followed the principle, developed in "Snackfood" (T 73/88, OJ 1992, 557), that adding non-essential features which merely limited the scope of protection did not invalidate the priority claim. This latter decision allowed a claim to enjoy priority despite containing an additional feature not disclosed in the earlier application.
In G 2/98 the Enlarged Board of Appeal, ruling on points of law referred by the President regarding the interpretation of Art. 87(1) EPC 1973, first considered whether interpreting "the same invention" narrowly was consistent with the relevant Paris Convention and EPC 1973 provisions. A narrow interpretation meant that the subject-matter of a claim which defined the invention in a European patent application - i.e. the specific combination of features in that claim - had to be at least implicitly disclosed in the application whose priority was claimed. The Enlarged Board held that a broad interpretation, distinguishing between those technical features which related to the function and effect of the invention and those which did not - with the result that an invention could still be considered "the same" even if a feature were amended, deleted or added - was inappropriate and prejudicial to a proper exercise of priority rights. To ensure a practice fully consistent, inter alia, with equal treatment for applicants and third parties, legal certainty and the principles for assessing novelty and inventive step, "the same invention" had to be interpreted narrowly and in a manner equating it to "the same subject-matter" in Art. 87(4) EPC 1973. This interpretation was underpinned by the Paris Convention and the EPC 1973, and was entirely consistent with opinion G 3/93 (OJ 1995, 18). The Enlarged Board therefore ruled on the points of law referred to it as follows:
The requirement for claiming priority of "the same invention", referred to in Art. 87(1) EPC 1973, means that priority of a previous application in respect of a claim in a European patent application in accordance with Art. 88 EPC 1973 is to be acknowledged only if the skilled person can derive the subject-matter of the claim directly and unambiguously, using common general knowledge, from the previous application as a whole.
The principles laid down by the Enlarged Board in G 2/98 mean that many statements made in decisions based in particular on T 73/88 (holding that adding non-essential and merely scope-limiting features did not invalidate a priority claim) are no longer relevant (e.g. T 16/87, OJ 1992, 212; T 582/91, T 255/91, OJ 1993, 318; T 669/93, T 1056/93 and T 364/95; see also "Case Law of the Boards of Appeal of the EPO", 3rd ed. 1998, p. 263 et seq. and 269 et seq.).
The older case law which devised the "novelty" and "disclosure" tests still applies following G 2/98 (and G 1/03 and G 2/03, see 1.2 below). This case law provides that two applications relate to "the same invention" within the meaning of Art. 87 EPC 1973 when they both contain "the same subject‑matter". The invention or subject‑matter of a previous application is to be considered identical to that of a subsequent one if the disclosure of both applications is the same (T 184/84). Disclosure in the previous application means that the subject-matter of the claims of the European application must be clearly identifiable in the documents of the previous application taken as a whole (T 81/87, OJ 1990, 250; T 359/92, T 469/92, T 597/92, T 296/93 and T 620/94). Identical wording is not required (T 81/87, OJ 1990, 250; T 184/84).