Qualitative analysis determines the minimal cut sets of your fault tree based on the gate logic. A cut set is a set of events that cause the top event to occur. A minimal cut set (MCS) is the smallest set of events, which, if they all occur, cause the top event to occur. If you remove any of the basic events from a minimal cut, the cut set would not remain. The basic events that belong to the cut sets provide information such as single point failures and the relative contribution of each cut set. Generally, cut sets that have the highest probability of occurrence are the ones that have the least number of basic events.