 These considerations show some uncertainty about how to combine various classificatory ideas. When Aristotle’s account became better known in the early thirteenth century, it was realized that the twelfth-century divisions between concupiscible and irascible emotions were not compatible with Aristotle’s idea of the contrary emotions of the same part of the soul. (See John Blund’s somewhat complicated attempt to solve this problem in Tractatus de anima 18–22.) An influential new taxonomic idea was introduced as a solution in the 1220s. (See the anonymous treatises De anima et potentiis eius, 47–48, and De potentiis animae et obiectis, 159, 164, as well as Philip the Chancellor, Summa de bono, 161). It was held that the objects of the contrary concupiscible acts were simply pleasurable or painful, and the objects of the irascible acts were also arduous (arduum), difficult to obtain or to avoid.