Subsection 8. The moving faculty.

This moving faculty is the other power of the sensitive soul, causing all those internal and external animal movements in the body. It is divided into two faculties: appetite and movement from place to place. Some hold that appetite is threefold. Natural appetite means an inclination such as a stone’s to fall downwards, or such actions as retention and expulsion, which depend on vegetative powers rather than sensation; it includes the appetite for food and drink, hunger and thirst. Sensitive appetite is common to humans and other animals.

The third is voluntary or intellectual appetite, which commands the other two in humans and restrains them, or at least should do. Yet it is usually held captive and overruled by them, and people are led like beasts by their senses, giving free rein to their cravings and various desires.

Through appetite the soul is led or inclined to pursue what the senses approve as good, or avoid what they consider evil. Its object is good or evil: it embraces one and rejects the other, according to the maxim that all things seek their own good, or at least what appears good. This power is inseparable from sensation, for wherever there is sensation there is also pleasure and pain.

Its organ is the same as that of common sense. It is divided into two powers or inclinations, the concupiscible and the irascible—or, as one writer translates them, coveting, and anger that attacks or resists. The concupiscible always desires pleasant and delightful things and recoils from what is disagreeable, harsh or unpleasant. The irascible turns away through anger and hatred, avoiding the object with anger and indignation.

All emotions and disturbances arise from these two springs. Although the Stoics make little of them, we regard them as natural and not to be resisted. Good emotions are caused by an object that is itself good. If present, it produces joy, which expands the heart and preserves the body; if absent, it causes hope, love, desire and longing. Bad emotions are simple or mixed. Simple ones concern some evil object present, as sorrow does: it contracts the heart, torments the soul, undermines the body’s well-being and hinders all its operations, causing melancholy and often death itself. Or they concern some future evil, as fear does.

From these two arise the mixed emotions and passions: anger, a desire for revenge; hatred, inveterate anger; zeal, which takes offence at anyone who harms what it loves; and malicious joy, a compound of joy and hatred, when we rejoice in other people’s misfortunes and grieve at their prosperity. There are also pride, self-love, rivalry, envy, shame, and others, of which I speak elsewhere.

Movement from place to place is a faculty that necessarily follows the other. Desire and aversion would otherwise be pointless if we had no power to pursue or avoid their objects by moving the body from place to place. Through this faculty, therefore, we move the body or any of its parts, and go from one place to another. To carry this out properly, three things are required: what causes movement, the means by which it moves, and what is moved.

What causes movement is either its efficient cause or its end. The end is the object desired or avoided, as when a dog seeks to catch a hare. The efficient cause in humans is reason, or imagination acting under it, which perceives good or bad objects. In other animals it is imagination alone, which moves appetite; appetite moves this faculty, which, through a wonderful bond established by nature and through the mediation of the spirit, commands the organ by which it acts.

That organ consists of nerves, muscles and tendons distributed throughout the body, contracting and relaxing as the spirits direct. The spirits move the muscles, or the nerves within them, and draw the tendon—and consequently the joint—to the intended position. What is moved is the body or some part capable of movement.

The body’s movements are various: walking, running, leaping, dancing, sitting and the like, referred to the category of bodily position. Worms creep, birds fly and fish swim. There are also movements of the parts, the chief being respiration, or breathing, which takes place as follows.

The outside air is drawn in through the windpipe and sent, through the action of the diaphragm, to the lungs. Expanding like a pair of bellows, they alternately draw it in and send it out to the heart to cool it; then they carry it back from there, now warmed, continually taking in fresh air. The pulse has a similar movement, about which I will say nothing, since many have written whole books on it.