Thomas Aquinas

“ For a power is called despotic whereby a man rules his slaves, who have not the right to resist in any way the orders of the one that commands them, since they have nothing of their own. But that power is called politic and royal by which a man rules over free subjects, who, though subject to the government of the ruler, have nevertheless something of their own, by reason of which they can resist the orders of him who commands. ”

“ I answer that, The sensitive appetite is one generic power, and is called sensuality; but it is divided into two powers, which are species of the sensitive appetite---the irascible and the concupiscible. In order to make this clear, we must observe that in natural corruptible things there is needed an inclination not only to the acquisition of what is suitable and to the avoiding of what is harmful, but also to resistance against corruptive and contrary agencies which are a hindrance to the acquisition of what is suitable, and are productive of harm. ”

“ The exterior senses require for action exterior sensible things, whereby they are affected, and the presence of which is not ruled by reason. But the interior powers, both appetitive and apprehensive, do not require exterior things. Therefore they are subject to the command of reason, which can not only incite or modify the affections of the appetitive power, but can also form the phantasms of the imagination. ”