For cases in which the amendment consists of the replacement or removal of a feature from an independent claim, the boards occasionally apply the test of decision T 260/85 (OJ 1989, 105). In T 260/85 it was stated that it was not permissible to delete from an independent claim a feature which the application as originally filed consistently presented as being an essential feature of the invention, since this would constitute a breach of Art. 123(2) EPC 1973. See also T 496/90, T 415/91, T 628/91, T 189/94, T 1032/96, T 728/98 (OJ 2001, 319; concerning the deletion of the feature "substantially pure"), T 1040/98, T 1034/02, T 2202/08 and T 1390/15.
In T 236/95 the board held that if the problem could not be solved without the features concerned, they could not be considered unimportant.
In T 784/97 the patent proprietor alleged that a prior art document would have made the skilled person aware that the disputed feature was not essential. The board held that whether or not a feature of an independent claim had to be seen as "essential" could not be a question of the prior art disclosure. Rather, what had to be decided was what a skilled person was taught by the originally filed documents.
In T 1515/11 the board observed that a feature could not be deleted from an independent claim if it had been consistently presented as an essential feature of the invention, since this would add subject-matter. In some cases there might be room for debate as to whether the application presents a feature as being essential to the invention or as being optional. However, there were also cases where, on purely formal grounds, the essentiality of a feature could not be doubted. One such case was where the applicant chose to include in an independent claim as filed a feature explicitly mentioning the problem, and affirming that the claimed subject-matter represents a solution to the problem. In particular, where a claim to a method included a feature explicitly defining that the method was carried out in a manner which solved the problem, to argue that this feature was not essential would be tantamount to arguing that in order to solve the problem, it was not essential to carry out the method in a way which solved the problem.
The board in T 648/10 confirmed the test set out in T 260/85. However, it observed that the EPC does not require the use of any particular tests when assessing whether subject-matter has been added. Instead, such tests are tools which may be helpful, in certain situations, in the assessment of whether subject-matter has been added.