According to the case law of the boards of appeal (see e.g. T 740/93; T 1709/06; T 2352/13; T 278/00, OJ 2003, 546 and T 1182/05) a "reasoned" decision should deal with all important issues of dispute. The grounds upon which the decision was based and all decisive considerations in respect of the factual and legal aspects of the case must be discussed in detail in the decision.
In T 292/90 the board held that a decision should discuss the facts, evidence and arguments which are essential to the decision in detail. It also has to contain the logical chain of reasoning which led to the relevant conclusion.
On inventive step; confirmed in many decisions, e.g. T 951/92, T 740/93, T 698/94, T 278/00 (OJ 2003, 546); T 70/02, T 963/02, T 897/03, T 763/04, T 316/05, T 1366/05, T 1612/07, T 1870/07, T 1997/08 and T 2366/11).
In T 70/02 the board held that reasoning does not mean that all the arguments submitted should be dealt with in detail, but it is a general principle of good faith and fair proceedings that reasoned decisions contain, in addition to the logical chain of facts and reasons on which every decision is based, at least some motivation on crucial points of dispute in this line of argumentation in so far as this is not already apparent from other reasons given.
In T 1123/04 the board was of the view that it was not enough if a board of appeal had to reconstruct or even speculate as to the possible reasons for a negative decision in the first-instance proceedings. As a rule, a decision within the meaning of R. 68(2) EPC 1973 should be complete and self-contained. The reasons were inadequate if the only arguments advanced by the examining division were unsubstantiated claims.