How to Think Like Aquinas

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by Kevin Vost


  Now, to get out of the weeds and down to the business of our human powers, I direct your attention to the diagram “Vegetative, Sensitive, and Intellectual Powers of the Soul.”

  We have started with the three powers of the vegetative soul, powers that form the apex of the pyramid of the soul of plant life, but merely the lowest foundation of the human soul. Every mature living plant, animal, or human on earth without some unusual deficiency or defect has, by its nature, those powers to nourish itself, to grow and repair tissue, and to reproduce its own kind. Indeed, while moderns might ponder how a spiritual soul (or at least a “mind”) can arise from a material body, in a very real sense, one of the soul’s most fundamental acts is to grow the appropriate body!

  Moving a crucial rung up this pyramid of perfection, we come to the level of the sensitive soul, which critters such as your dog or cat possess. As fond as they may be of eating, growing, or finding mates, chances are they do many other things besides. After all, that’s why you chose them, and not tomato plants, to be your family pets. And of course, the distinguishing characteristic of a sensitive soul does not merely mean that it can get grumpy or be easily slighted. It refers to the fact that animals — but not plants — possess the powers of sensation.

  The first of these is touch, and some primitive animals may possess it without the other four senses. One of Thomas’s examples is that of the homely oyster. Our human powers of touch are very well developed, and we can use them to sense all kinds of things, such as heat, pressure, vibration, and more. Of course, our dogs and cats share the powers of touch with us as they do the other four senses of smell, taste, hearing, and vision. In fact, my dogs can smell and hear a lot better than I can, and I’d wager that the same applies to yours. Also, we and other animals have very obvious bodily organs that serve these five senses — skin, noses, tongues, ears, and eyes — along with the less obvious nerve networks and brain centers to which they connect.

  Beyond the “Sixth Sense” to the Seventh, Eighth, and Ninth

  Our five external senses provide the pathways to knowledge and understanding, but they are far from the end of the road in themselves. Please allow me to illustrate with a simple scenario.84

  I see two patches of white, hear flapping sounds, feel dampness, smell a musty odor, and taste a hint of salt. Whatever could it be? My senses have not told me much else. Now I perceive that each patch stands about one foot tall, is just a few inches from me, has four downward tubular projections, and one in the back that is moving quickly from side to side. Still don’t know what they are? Then let me introduce you to our dogs Lily and Lucy, who have just come inside from playing in wet snow and are shaking themselves dry.

  Note how the disparate bits of information coming in from our separate external senses don’t necessarily make much sense until they are all put together and integrated by what St. Thomas called the sensus communis or “common sense.” He is not talking about the kind of practical, down-to-earth, common sense that your parents always encouraged you to use, but a special, synthesizing power of the human and higher animal soul. It is this common sense that enables us to perceive as one thing (two in this example!) the many data provided by our diverse external senses. In modern psychological terminology, the senses produce sensation, but the common sense — the first of what Thomas calls the four internal senses, produces perception. Perception derives from the Latin word percipere, “to seize wholly” (as a whole, unified thing — in this case the two whole things, our dogs Lily and Lucy).

  So, the common sense does indeed make sense, but so do three other internal senses in the same tier of our pyramid. I’ll bet you’ve formed some kind of fuzzy mental image of little Lily and Lucy, have you not? To help you a bit, Lily is a five-year-old miniature American Eskimo. She is a fourteen-pound bundle of energy encased in thick, fluffy snow-white fur. Lucy, age nine, also a miniature, with sleek, silvery white hair, is very laid back, a twenty-pound “couch-cuddler” with the classic bearded snout that earned her breed the name of Schnauzer. The mental images85 you have now formed are courtesy of a second internal sense called, quite appropriately, imagination. Indeed, Aristotle believed that “the soul never thinks without an image,”86 and the Angelic Doctor agreed.

  Humans and higher animals have the power to hold on to sense perceptions after the objects that produced them are no longer present to act on the sense organs. This basic power of forming images, as we just saw, is called imagination. We can say that the five external senses and the common sense are “presentational” powers, since they convey and present to us particular things that are present in the world outside us (and at times, too, things present in the world within us, as when we hear not our dogs but our stomachs growling). The internal sense of imagination is the first of our “re-presentational” powers, since the images serve as re-presentations of original experiences that free us from the immediate present. We can imagine Lily and Lucy, for example, even when they’re not hanging around. Further, the imagination has another very imaginative trick up its sleeve: its ability to combine and form images of things that we have never experienced. Nobody has ever seen an American Eskimo or a Schnauzer as big as a house (thank God!), but we can easily imagine them. We can create novel imaginary images, too, by combining in various ways the images of virtually anything we have ever seen — or imagined!

  A third internal sense is memory. Also re-presentational, it builds up powers of the imagination with temporal, emotional, and intellectual components. Through the power of memory, we realize that the objects of our images are not only absent, but they happened in the past. Our personal memories are also embedded in the context of the emotional experiences in which they occurred. Call to mind your grandmother or your best childhood friend, and you are likely to feel something, too.

  And for human beings, the intellect also comes into play. Surely you will recall from our last chapter that not only can we hold on to past impressions via sensory memory, as do other animals, but we possess powers of recollection, whereby the thinking powers of the highest tier of our pyramid reach down, so to speak, and give us a hand in figuring out strategies for recalling old things and remembering new ones. Further, we can remember not only particular things we have sensed in the past but also universal concepts and abstract ideas, as we shall soon consider.

  Animals and humans share in a final, most vital inner sense. Not only do we perceive things as having certain sensible qualities; we also perceive whether they are good or bad, desirable or undesirable, and useful or harmful to us. In animals, this is called the estimative sense (vis aestimativa) or animal prudence. St. Thomas notes that the lamb senses not only things such as the size, shape, color, sound, and smell of the wolf; it senses the dangerousness of the wolf, which is not present in the information derived from the external senses alone. This estimative sense is the cognitive component of instinct.

  Even we humans are naturally attracted to or repelled by some objects before we have time to reflect upon them with our intellects. (In my own case, the sudden presence of a snake would trigger this response; for my wife, a mouse does the trick.)87

  In humans, this important power, so crucial to the preservation of life, is also subject to guidance by the intellect. It is called the cogitative sense (vis cognitiva) or “particular reason.” It is called particular reason because it is subject to guidance by the reasoning powers of the intellect (to be addressed later), but its focus is on particular things, rather than on universal concepts.

  As the common sense integrates the information from the five external senses, so too does the cogitative sense integrate the information from the external senses and the higher-order internal senses of the common sense, imagination, and memory, leaving the cogitative sense but one step removed from the powers of the intellectual soul.

  There you have it: a brief look at the internal senses. But more remains in this tier of our pyramid within the sensitive powers
of the soul.

  Hooked on a Feeling? Do the Locomotion

  The estimative or cogitative sense that allows Lily and Lucy, or you and me, to determine that certain things are good for us or bad for us sure wouldn’t serve much purpose if all we could do is sit there like a rutabaga, calm and content all the time, rooted to one spot in the earth. Two more fundamental powers of the sensitive soul separate the animal and the plant worlds.

  The first are the source of what Thomas called the “passions” and what we are more likely to call emotions or feelings. Even though we may experience them intensely, and they may motivate us to action, Thomas uses the word “passion” because the word implies passivity, in the sense that our bodies and souls have receptivity — the ability to be influenced by the objects we perceive outside ourselves, whether to draw us toward them (as in the passion of love) or repel us (as in the passion of hate), while members of the plant world just sit there soaking up the sunshine and drawing in nutrients, unmoved by anything else.

  Our pets and the beasts in the wild have passions, though, and so do we. The passions are movements of the sensitive appetites of the soul when we are faced with good or evil. The two primary powers that produce all our passions are the concupiscible appetite, fueled by love, whereby we have an affinity for the good and are repelled by evil, and the irascible appetite, fueled by hate in the sense that it motivates us to remove obstacles barring us from the things we love. In the last analysis, love conquers all and is the primary passion that moves us, since even the passions of the irascible appetite, as noted above, serve to remove whatever obstacles come between us and the things that we love.

  We can see these appetites very clearly in action in the animal world, where so much behavior is motivated by the concupiscible appetite toward seeking the goods of food, mates, and territory (which provides access to food and mates), while most aggression is motivated by the irascible appetite, centered on conflicts over those same goods. Humans, too, have such appetites, as I’m sure you will agree from your own experience. Again, as is the case for many higher sensitive powers, though, while animals are guided by instinct and training, our higher reasoning capacities can step in to regulate these appetites (though it is not always easy).

  Finally, for the powers of the sensitive soul, it is time to do the locomotion, so to speak. Having appetites and aversions would be of no use if we did not have a means to act on them, to go after good things and flee or fight against evils. Aristotle argued that nature does not act in vain, and St. Thomas agreed. This final power of the sensitive soul is that of locomotion or self-movement. Unlike plants and all but some of the simplest of animals rooted to one spot, animals and humans are able to move about, moving their whole bodies or limbs to seek or avoid things as they see fit.

  So much, then, for a brief introduction to the powers of the sensitive soul. It is time to take the most crucial leap up our pyramid of powers of the soul to the peak, from which only humans among all species on earth have the capacity to oversee and to guide the other powers. We’ll start at the top.

  The Intellectual Soul and the Road to Understanding

  The thinking capacities of animals stop at the level of phantasms or images. These images capture and re-present particular things and events or particular dogs, such as Lily, for example. But we can speak of dogs in general, too. You have probably never met Lily, but you understand what I mean when I talk about her. In fact, as for all the words I use in this book, you either understand them, or if you don’t, you possess the capacity to ask someone what they mean or to look them up. Dogs, such as Lily and Lucy, and all other animal species (even parrots) produce no words of their own. Further, you and I can also talk about abstractions, such as truth, justice, and the American way, even though we can’t see, hear, touch, taste, or smell them. This is the gift of the intellectual soul, and it possesses two main powers that allow us to grasp abstract, universal, and immaterial realities.

  Just as the internal senses produce images from sense impressions, the agent or active intellect produces abstractions from those images. The Latin word intellectus derives from intus (inside) and legere (to read). The agent intellect looks below the surface of experience to abstract (draw forth) the essences of objects that have stimulated our senses. It sorts the jumble of sensory data to perceive a thing’s essential, universal nature. The agent intellect’s gaze is unobstructed by particular, accidental features; it’s like an X-ray that looks through the externals to see the reality below the appearance. My eyes look at little, fluffy Lily and at sturdy, bearded Lucy, her Schnauzer “sister,” and my agent intellect detects the quiddity — the “whatness,” or, in this case, the substantial “dog-ness” — that they share, despite their accidental, nonessential differences. The abstraction produced by the agent intellect is form without matter. It is immaterial and not the product of any particular bodily organ (not even the brain), as the products of the senses are, as will be spelled out in our next section.

  But the intellect has not finished its workings on their white fluffy or silky furriness.

  The last stop on the road to human understanding is the possible intellect.88 Just as the percepts of the senses and common sense provide the data for images, the abstractions of the agent intellect provide the fodder for the ideas or concepts of the possible intellect. The abstraction is then received by the powers of the possible intellect, which stimulates it to produce a product of its own, which we call a concept or idea. Get the idea?89 Maybe this will help:

  The Road to Understanding

  Level of Soul

  Power

  Product

  Sensitive

  External senses

  Sensation

  Common sense

  Perception

  Imagination

  Memory

  Cogitative sense

  Phantasm (or image)

  Intellectual

  Agent intellect

  Abstraction

  Possible intellect

  Idea (or concept)

  Maybe it will help a little more to view this as a process:

  The Birth of an Idea90

  Thing or object

  Faculties

  Outer sense and Common sense

  →

  Imagination

  Memory

  Cogitative sense

  Agent intellect

  Possible intellect

  Product

  Percept →

  Phantasm →

  Abstraction →

  Concept or idea

  Description

  Impressed sensible species

  Expressed sensible species

  Impressed intelligible species

  Expressed intelligible species

  Immaterial Thoughts, Indestructible Soul

  Let’s note that as we move along the road to human understanding, we start with particular things and end with universal ideas. We start with the sensations produced by material, bodily organs, and end with concepts of a purely spiritual, intellectual soul. In sensations, forms are separated from matter, but not from the conditions of particular material things: if you see a rock, you see it because it’s sitting in front of you. In the ideas of th
e intellect, forms are separated from matter and from its particular conditions as well: if you’re thinking about rock in general, your mind “sees” an image of rock, whether one is in front of you or not. Sensations are particular and concrete; ideas are universal and abstract. Since the intellect can potentially know the essence of all material bodies, it cannot itself be a material organ.91 As Thomas points out:

  If the intellectual soul were composed of matter and form, the forms of things would be received into it as individuals, and so it would only know the individual; just as it happens with the sensitive powers which receive forms in a corporal organ; since matter is the principle by which forms are individualized. It follows, therefore, that the intellectual soul — and every intellectual substance which has knowledge of forms absolutely — is exempt from composition of matter and form.92

  Let’s note one other important implication of the immateriality of the human intellectual soul — in fact, it’s the most important of all possible implications. Because the human soul is immaterial, it has no parts that can decompose. Barring an act of annihilation by God Himself, the soul is also immortal. How important it is, then, to act in ways pleasing to God, who breathed immortality into our spiritual souls!

  Where There’s a Free Will, There’s a Uniquely Human Way

  Perhaps you’ve noticed one last power near the top of the pyramid yet to be explained. Very good then; we’ve got one last bit of explaining to do. We’ve seen how the intellectual powers of the human soul are unique among those of all creatures on earth. Being composites of material bodies and spiritual souls, we have a uniquely human way of knowing that is inaccessible to irrational animals. Angels have higher intellects. As purely spiritual beings, their knowledge of what things are comes all at once to them as instantaneous intuition. They don’t require sensory data and the multiple steps of cognitive processing and reasoning that we do.93 Human beings not only have a unique way of knowing; we have a unique way of acting as well. If we want to know which human acts lead to happiness, we must learn about the human will. And since there’s a will, you can rest assured that St. Thomas has provided a way to understand it.

 

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