Dual-process theorists posit that human thinking involves two kinds of mental processing: System 1 (an intuitive process), which is generally reliable but can lead to fallacies and biases, and System 2 (a reflective process), which can, at its best, allow human reasoning to follow normative rules. One of the most significant problems with the dual-process theories is whether System 2 can control the outputs of System 1, which are sometimes non-normative. Generally, when the output of System 1 entails a single emotion such as fear, this emotion is less likely to be revised or suppressed by System 2. I introduce two major periods as natural experiments of history: The period between the 17th and 18th centuries in Europe and the period after the Second World War. Both periods are characterized as the time when war, murder, violence decreased and sympathy for the victims and awareness of human rights grew. The prevalence of novels, which enhanced the mindreading (a function of System 1) of victims, was an important factor in the former case. The growth of people’s intelligence (linked to System 2) was an important factor in the latter case. The methodology of the natural experiment in history gives a significant implication to the issue of System 2 control.
