R. 42(1)(c) EPC (former R. 27(1)(c) EPC 1973) stipulates that an application's description must "disclose the invention, as claimed, in such terms that the technical problem (even if not expressly stated as such) and its solution can be understood, and state any advantageous effect of the invention with reference to the background art". As long ago as T 26/81 (OJ 1982, 211), R. 27(1)(c) EPC 1973 was recognised as clearly binding. The boards' case law, and correct application of the problem and solution approach (see T 1/80, OJ 1981, 206; T 24/81, OJ 1983, 133), show that objective criteria must be used to determine the technical problem, i.e. the problem which can be seen to have been actually solved in the light of the closest prior art which may be different from the prior art which was at the disposal of the inventor (T 576/95). These objective criteria may be specifically defined by assessing the technical progress made in the subject-matter of the application against the closest prior art (T 20/81, OJ 1982, 217; T 910/90). A comparison of the problem indicated in the application with that indicated in a prior document must avoid an unduly abstract approach far removed from the practical thinking of the person skilled in the art (T 5/81, OJ 1982, 249).

In identifying the problem it is not permissible to draw on knowledge acquired only after the date of filing or priority. According to T 268/89 (OJ 1994, 50) the non-effectiveness of a prior art apparatus or method recognised or alleged only after the priority or filing date could not be drawn on in formulating the problem, particularly where that problem was adduced in support of inventive step in a "problem invention" (see T 2/83, OJ 1984, 265). Inventive step had to be assessed on the basis of the skilled person's knowledge before the priority or filing date (see also T 365/89).

For the purpose of the problem and solution approach, the problem must be a technical one that a skilled person in the particular technical field might be asked to solve at the priority date. The technical problem may be formulated using an aim which is to be achieved in a non-technical field, and which is thus not part of the technical contribution provided by the invention to the prior art (T 641/00, OJ 2003, 352; T 154/04, OJ 2008, 46); see also in this chapter I.D.9.1. "Treatment of technical and non-technical features".

In T 1639/07 the board held that the objective technical problem must be derived from physical, chemical etc. effects directly and causally related to the technical features of the claimed invention. An effect could not be validly used in the formulation of the technical problem if the effect required additional information not at the disposal of the skilled person even after taking into account the content of the application in question. See also T 584/10.

In T 377/14 the board, referring to T 344/89, held that the problem did not have to be explicitly disclosed in the application as filed; it sufficed if it was foreshadowed therein.

In T 1841/11 the board held that a problem which is not mentioned in the application in relation to the claimed feature, and which would not arise over the whole ambit of the claim, or even for those embodiments described in detail in the application, cannot be considered to be a suitable choice.

In T 632/10 the board considered that an objective technical problem solved by the invention was to implement a digital signature system compliant with the requirements of Section 17 of the German Signature Law (SigV). The appellant (applicant) argued that the SigV might not be relevant for a European patent application, for which states other than Germany could be designated. The board was unconvinced by this argument. Even if an invention happened to be obvious only for skilled persons of German nationality or residence, it would still lack an inventive step within the meaning of Art. 56 EPC 1973. The fact that the SigV was valid only within Germany thus had no bearing on its status as prior art or its relevance for the assessment of inventive step outside Germany.

In T 1422/12 claim 1 related to crystalline forms of tigecycline. The board referred to the established case law that the technical problem has to be determined on the basis of objectively established facts, since for the determination of the objective technical problem, only the effect actually achieved vis-à-vis the closest prior art should be taken into account (T 13/84, OJ 1986, 253 and T 39/93, OJ 1997, 134). In this connection, any effects may be taken into account, so long as they concern the same field of use and do not change the character of the invention (T 440/91). The formulation of the technical problem to be solved fell well within the framework of the invention as disclosed in the application in suit. That the more specific problem of improved stability with respect to epimerisation was not mentioned in the application as originally filed was irrelevant (T 39/93), since improvement of stability by avoidance of epimerisation, and, as a consequence, improved biological activity was clearly recognisable by the skilled person as a desirable effect for a tetracycline antibiotic.

In T 519/07, the board held that, where comparative tests were chosen to establish inventive step on the basis of an effect produced over the claimed area, the comparison with the closest prior art had to show convincingly that the effect was attributable to the feature distinguishing the invention. The aim of such comparison was to demonstrate that the technical effect had its exclusive origin in the feature characterising the invention in the claims (see also T 1682/15). That had not been shown in the case in point. It could not be concluded from the comparisons that the technical problem defined by the respondent (patent proprietor) had actually been solved by the claimed processes. The technical problem therefore had to be reformulated (see also T 479/06, a case concerning a cosmetic or dermatological emulsion, in which the board observed that the claimed emulsions had been tested using a different test protocol from that applied when testing one of the emulsions disclosed in the closest prior art).

In T 2579/11 the board considered the probative value of comparative tests carried out by the patent proprietor to show that the claimed invention actually solved the problem of improving biodegradability. The proprietor had not divulged the details of the test protocol applied, citing commercial reasons. The board ultimately found that the test results were neither verifiable nor plausible and therefore insufficient to establish that the problem had been solved successfully.

In T 943/13 the board came to the conclusion that the causal relationship between the substance or composition on the one hand and the therapeutic effect achieved on the other hand was decisive for the assessment of inventive step of further-medical-use claims. Indeed the board considered that the objective technical problem was the provision of the claimed therapeutic effect by a different/alternative means. The board acknowledged that the objective technical problem might indeed be the provision of an alternative composition if claim 1 was a "normal" product claim directed to a substance or composition.

In T 87/08 the board stated that Art. 56 EPC requires that the assessment of inventive step is made "having regard to the state of the art". Accordingly, a decision is not sufficiently reasoned in the sense of R. 68(2) EPC 1973 (R. 111(2) EPC 2000) if the chain of reasoning to justify the finding of lack of inventive step merely states that a purported effect has not been achieved, i.e. this technical problem had not been solved, without reformulating the problem in a less ambitious way and without assessing obviousness of the claimed solution to that reformulated problem in the light of the cited prior art (T 1079/08, T 306/09, T 2375/10).