 Section 2.2  drew attention to McCarthy’s proposed goal of formalizing common sense reasoning. The brief discussion above in  Section 3.1  suggests that monotonicity may be an obstacle in pursuing this goal. An additional motive was found in  Minsky 1974,  which was widely read at the time. This paper presents an assortment of challenges for AI, focusing at the outset on the problem of natural language  understanding.[16]  Minsky advocates frame-based knowledge representation  techniques[17]  and (conceiving of the use of these representations as an alternative to logic), he throws out a number of loosely connected challenges for the logical approach, including the problem of building large-scale representations, of reasoning efficiently, of representing control knowledge, and of providing for the flexible revision of defeasible beliefs. In retrospect,  most AI researchers would tend to agree that these problems are general challenges to any research program in AI (including the one Minsky himself advocated at the time) and that logical techniques are an important element in addressing some, perhaps all, of the issues. (For instance, a well structured logical design can be a great help in scaling up knowledge representation.)