This position paper addresses the question of why, whilst the human brain is apparently geared to process information of mixed polarities, human reasoners sometimes fail to deal appropriately with simple instances of mixed evidence or mixed prospects. From a dual???process perspective of thinking, two mental routes for bipolar information processing are identified. One is biologically acquired and evolution tied, and the other is the product of a cultural elaboration of rational norms. In between the two routes, a blind spot accounts for failures of bipolar information processing.