 A detailed early thirteenth-century classification on the basis of the notion of arduum with contrary emotions was developed in John of la Rochelle’s Summa de anima. He regarded emotions as the acts of two moving powers, the concupiscible and irascible, both with several types of reaction divided into contrary pairs. The concupiscible pairs are associated with the contrary dispositions of liking (placentia) or dislike (displicentia) and irascible emotions with strength (corroboratio) and weakness (debilitas). These correspond to different types of estimative acts which are their causes. The new systematic idea was to use these dispositions of feeling and corresponding behavioral reactions as classificatory principles. The emotions of the concupiscible power are classified as follows: