Thomas Aquinas divides the sensory appetite into two powers: the irascible and the concupiscible. The irascible power moves creatures toward arduous goods and away from arduous evils, while the concupiscible power moves creatures toward pleasant goods and away from non-arduous evils. Despite the importance of this distinction, it remains unclear what counts as an arduous good or evil, and why arduousness is the defining feature of the division. The aim of this paper is twofold. First, I argue that an arduous (...) object is one that is difficult and important for the creature. Second, given this proper understanding of arduousness, I highlight the shortcomings of the standard interpretation of Aquinas’s argument for the irascible-concupiscible distinction and suggest an alternative. I argue that Aquinas grounds the distinction in the distinction between useful and pleasant goods. I explain how these distinct goods allow arduousness to be the defining feature of the irascible-concupiscible division. (shrink)