1.4.4 The essentiality or three-point test
In T 331/87 (OJ 1991, 22) the board, building on T 260/85 (OJ 1989, 105) set out a three-point test. The board held that the replacement or removal of a feature from a claim might not be in breach of Art. 123(2) EPC 1973 if the skilled person would directly and unambiguously recognise that (1) the feature was not explained as essential in the disclosure, (2) it was not, as such, indispensable for the function of the invention in the light of the technical problem it served to solve, and (3) the replacement or removal required no real modification of other features to compensate for the change (frequently applied until 2012, see e.g. T 708/07, T 775/07, T 2359/09, T 747/10, T 207/10; now seldom applied, but see T 1906/12). This test is sometimes referred to as the essentiality test (see e.g. T 2359/09, T 2599/12, T 2489/13). Note that the Guidelines (EPC Guidelines H‑V, 3.1 – April 2025 version) contain a modified three-point test.