The Hierarchy of Souls

This article is part of an anthropology series entitled “Created in the Image and Likeness of God”.  You can click on the tag at the end of the article to see all the articles in the series.

In my last essay I discussed the body-soul unity.  In this essay, I will be looking at some of the particular traits of human beings that make us unique among living things.

Following Aristotle, St. Thomas Aquinas outlined different faculties of the soul.  He divided the faculties of the soul into five main categories or ‘powers’: vegetative, sensitive, locomotive, appetitive and intellectual.  He saw that in the natural world there was an increasing complexity of design and function.

The most basic living things, for example plants, only possessed the vegetative faculties.  The vegetative faculties included basic life processes like nutrition, growth and reproduction.  All plants have built into their biology, processes that allow them to feed themselves through their roots (water and minerals) and leaves (carbon dioxide and sunlight), without which they would die.  They also have processes that allow them to grow, sprout flowers, pollinate and produce seeds to create a new generation.

Powers of the human soul
A diagram showing St. Thomas’ s philosophy of the division of powers in the human soul.

One level up from plants are animals that don’t move.  An animal that I think most readers would be familiar with is the sand-dollar.  These animals have all the faculties of plants: nutrition, growth and reproduction, but they have an additional faculty of sensitivity.  They can use senses like smell and touch, to interact with their surroundings, and understand what is going on around them.

In addition to the vegetative (plants) and sensitive (sea-dollars) powers, there is the power of locomotion.  This pertains to most animals.  Most animals carry out the basic life processes of plants, but they are also able to interact with their surroundings and move about.  Through the senses of touch, taste, hearing, sight and smell they are aware of the environment around them in a way no plant could ever be.  Plants, to be sure, will ‘know’ if the ground they have been planted in is dry.  But they could never smell an animal nearby or, far-less, see a plant nearby with whom they might want to cross-pollinate.  They can only produce pollen and let it blow in the wind, ‘hoping’ that it finds another fertile flower.  Animals on the other hand, must use their senses and ability to move around to help them carry out their functions of feeding, sleeping, hunting and mating.

Over-arching all of these faculties is the appetitive power.  This is the faculty in the soul that it allows it to identify or ‘feel’ what is good for it.  It penetrates all the other faculties to some extent, and it can be said to be the master power.  In plants and animals, the appetite is what drives the other faculties to carry out their function.  When a dog is hungry, he looks for food.  Put another way, his vegetative appetite kicks in and he sets about using his sensitive and locomotive powers to help him continue to carry out his biological functions of living, moving and being a good companion.

The fifth power that St. Thomas outlines is the intellectual power.  This power is unique to human beings.  No other animal or plant has this power.  It allows human beings to reason, to find patterns, to intuit, to read between the lines (a literal translation of  the latin word ‘intellectus’).  Animals have cognitive powers at the sensitive level alone, which allow them to have a certain practical reason or instinct.  For this reason, a bird does not have to be taught which materials will be suitable for its nest.  However, a bird could not reflect on its ability to build a nest or suggest laws that govern the stability of any given nest.

It is important to know and understand the different powers of the human soul, as it will help us have a better idea of how to be happy and well.  It is only when all the faculties of man are working together, harmoniously, that man will find true happiness and well-being.  When man understands his function, in this world, and beyond, he can order his acts toward the right end and so fulfill his role and vocation as a thinking, reasoning animal.

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