Therefore the irascible and concupiscible appetites do not obey reason. Further, as the appetitive power is inferior to the rational part of the soul, so also is the sensitive power. Therefore, in like manner, neither do the powers of the sensitive appetite, the irascible and concupscible, obey reason. To the will also is the sensitive appetite subject in execution, which is accomplished by the motive power. In this way, therefore, the irascible and concupiscible are subject to reason.
Sensuality is signified by the serpent, in what is proper to it as a sensitive power.
But the irascible and concupiscible powers denominate the sensitive appetite rather on the part of the act, to which they are led by the reason, as we have said. 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. And so, the soul is said to rule the body by a despotic power, because the members of the body cannot in any way resist the sway of the soul, but at the soul's command both hand and foot, and whatever member is naturally moved by voluntary movement, are moved at once. For the sensitive appetite is naturally moved, not only by the estimative power in other animals, and in man by the cogitative power which the universal reason guides, but also by the imagination and sense.