Subsection 5. The soul and its faculties.

Following Aristotle, the soul is defined as the fulfilment or first actuality of an organized body with the capacity for life, a definition most philosophers accept. But many questions arise about its essence, its underlying subject, its seat, its divisions and its subordinate faculties.

Of all things, the soul’s essence and precise nature, whether in humans or animals, are the hardest to discern, as Aristotle himself, Cicero, Pico della Mirandola, Toledo and other more recent philosophers admit. We understand everything through the soul, yet cannot grasp what the soul itself is. Some therefore posit one soul divided into three principal faculties; others posit three distinct souls. Piccolomini and Zabarella have recently debated this question at length.

Paracelsus maintains that there are four souls, adding a spiritual soul to the three accepted faculties. Campanella, in his book On the Sense of Things, works hard to demonstrate and prove this opinion, arguing that corpses bleed in the murderer’s presence, and offering many similar arguments. Others hold that all creatures have the same kind of soul and differ only in their organs; animals possess reason just as humans do, though in a smaller measure because of some deficiency in their organs. Others question whether the soul is wholly present in the whole body and wholly present in every part. Zabarella, among others, discusses this at length.

The usual division of the soul is into three principal faculties: vegetative, sensitive and rational, giving three distinct kinds of living creature—vegetative plants, sensitive animals and rational humans. How these three principal faculties are distinguished and connected seems beyond human understanding, as Taurellus, Philip, Flavius and others suppose. The lower faculty can exist alone, but the higher cannot exist without it. Thus the sensitive includes the vegetative, and the rational includes both, which are contained within it, as Aristotle says, like a triangle within a quadrilateral.

The vegetative faculty, the first of the three, is defined as a substantial actuality of an organized body by which it is nourished, grows and produces another like itself. This definition specifies three operations: nourishment, growth and reproduction. The first is nutrition. Its object is nourishment—food, drink and the like—and its organ is the liver in creatures with sensation, or the root or sap in plants. Its function is to turn nutriment into the substance of the body being nourished, which it does through natural heat. Four subordinate functions or powers belong to nutrition: attraction, retention, digestion and expulsion.

Attraction is an assisting faculty that draws food into the stomach as a lodestone draws iron, or a lamp draws oil. This attractive power is essential in plants, which suck moisture through their roots as through a mouth, into the sap as into a stomach. Retention holds the food once it has been drawn into the stomach, until it is digested; if it passed straight through, the body could not be nourished.

Digestion is performed by natural heat: as a torch’s flame consumes oil, wax or tallow, so natural heat transforms and digests the nutritive matter. Its opposite is indigestion, caused by insufficient natural heat. There are three kinds of digestion: ripening, boiling and roasting.

Ripening is especially evident in the fruit of trees, which is said to be ripe when its seeds are ready to be sown again. Its opposite is rawness or incomplete digestion, to which gluttons, lovers of luxury and idle people are especially prone. They take no exercise to kindle their natural heat, or else smother it as too much wood puts out a fire.

Boiling is the simmering of food in the stomach through this natural heat, as food boils in a pot; its opposite is corruption or putrefaction. Roasting is the processing of internal moisture by heat; its opposite is incomplete roasting.

Besides these three operations of digestion, there is a fourfold sequence of digestive processing: mastication, or chewing in the mouth; the conversion of chewed food into chyle in the stomach; third, its conversion in the liver from chyle into blood, called sanguification; and last, assimilation, which takes place in every part. Expulsion is the power of nutrition that eliminates all surplus waste and remnants of food and drink through the intestines, bladder and pores: by purging, vomiting, spitting, sweating, urine, hair, nails and so on.

As the nutritive faculty nourishes the body, so the faculty of growth—the second operation or power of the vegetative faculty—increases its size in every dimension, length, breadth and thickness, until it reaches its proper proportions and complete form. It has its appointed period of growth, as it does of decline, and that is certain, as the poet observes:

Each has his appointed day; for everyone The time of life is brief and cannot be restored.

A span of life is set for everyone; It is but short, and none can live beyond it.

The last of these vegetative faculties is reproduction, which through seed produces another like itself, perpetually preserving the species. They assign three subordinate operations to this faculty, the first being to turn nourishment into seed, and so on.

Necessary accompaniments or conditions of this vegetative faculty are life and its absence, death. Natural heat is essential to preserving life, though dryness, moisture and the other primary qualities also play a part. This heat exists in plants too, as their growth and fruiting show, although it is harder to perceive. In every body it needs innate moisture to sustain it and prevent its exhaustion. Our climate, country, bodily constitution, and good or bad management of the six non-natural things contribute greatly to its preservation.

For as this natural heat and moisture diminish, so does life itself. Unless cut short beforehand by some violent accident or interrupted through our own fault, it is finally dried up by old age and extinguished in death for want of fuel, like a lamp without oil to sustain it.