A typology of two-alternative decision-making situations is presented. Given the available knowledge of a decision, some situations represented by states of the typology lead immediately to a decision, while others can be transformed by adding evidence. The states in the typology are associated with appropriate transformations. By classifying a decision-making situation in the typology, one can find actions to effect the transformation of an intractable decision-making situation into a tractable one. This opens the possibility of sophisticated control for knowledge systems by table lookup.