Thomas Aquinas: On the Motion of the Heart (De Motu Cordis)
Translation © Gregory Froelich
Since everything that is moved must have a mover, the problem arises: What moves the heart and exactly what kind of movement does it have?
For first of all, it does not seem that any soul moves it. The nutritive soul does not move it, since its activities are generation, nutrition, growth and diminution. But the motion of the heart is none of these. Moreover, the nutritive soul is also in plants, but the motion of the heart belongs to animals only.
Neither do the sensitive and intellectual souls move it, since sense and intellect move only by means of appetite. But the motion of the heart is involuntary.
In fact the heart's motion does not even seem to be natural, since it is made up of opposite types of movements: push and pull. But natural motion is toward one opposite, not both, such as the motion of fire, which is only up, and that of earth, which is down. On the other hand, to say that the motion of the heart is violent is irrational. For obviously if we do away with this motion, we end up doing away with (i.e., killing) the animal, but nothing violent preserves a nature. Indeed, the heart's motion must be most natural, since animal life is inseparably united to it.
Now some who say that it is a natural motion claim that its source is not the particular nature of the animal, but some outside universal nature, or an intelligence.
But this is absurd. For in all natural things, both common and specific properties in them result from an intrinsic principle. Natural things, by definition, have their principle of motion in them. But nothing is more proper to animals than the motion of the heart, for once it stops, the animal dies. Therefore, it follows that the principle of such a motion must be in the animal.
In addition, when the motions in lower bodies are caused by a universal nature, such motions are not always present in them. Take, for example, the ebb and flow of ocean tides, which result from the motion of the moon and change in accord with it. But the motion of the heart is always present in the animal. Therefore, the heart's motion does not result from a separate cause but from an intrinsic principle.
Some others say that the principle of this motion in the animal is heat, which being generated by spirit moves the heart. But this is unreasonable. For the deeper principle is more likely to be the primary cause. But the motion of the heart is a deeper principle in the animal and more contemporaneous with life than even warmth. Therefore warmth is not the cause of the heart's motion, but on the contrary the heart's motion is the cause of warmth. Thus the Philosopher says in On the Motion of Animals: "What is about to create motion, not by means of alteration, is of this kind" (c. 10 703a24-25).
There is another way of responding to their opinion: A fully developed animal, one that is capable of moving itself, is more like the whole universe than anything else. This is why man, who is the most fully developed of animals, is called by some a microcosm. Now in the universe the first motion is local motion, which causes alteration and the other motions. So we more clearly see in animals that local motion is the principle of alteration, and not the contrary. As the Philosopher says in the Physics: "For all natural things, to move is to live."
Yet another way: the essential is prior to the accidental. But the first motion of the animal is the motion of the heart. Heat, on the other hand, does not move something else into another place except incidentally. For an essential feature of heat is to warm, and incidentally to move something from one place to another. Therefore, it is ridiculous to say that heat is the principle of the heart's motion. Rather, we need to find a cause that is in its essential makeup a principle of local motion.
Therefore, from this point on we should take as a principle of our investigation what the Philosopher says in Physics 8 (254b16-20): "Of those things whose principle of motion is in themselves, we say they are moved by nature. So, even when an animal as a whole moves itself by nature, its body can sometimes be moved both by its own nature and by something outside its nature. For there is a difference between the kind of motion that it happens to undergo and its elemental composition." For when an animal descends it undergoes a motion natural both to it as a whole and to its body, since in the body of an animal the dominant element is heavy, whose nature is to move downward. But when an animal rises it undergoes a motion natural to it as a whole, because its source is an intrinsic principle, namely the soul; nevertheless, this motion is not natural to the heavy body. This is why an animal tires out more in this kind of motion.
Another point to consider is that animals move from place to place because of their desires or intellect, as the Philosopher teaches in the third book of On the Soul (433a9-b30).
Therefore, in animals that act only by nature and not by intent, the whole process of motion is natural. For the sparrow naturally makes a nest and the spider a web. But only man acts from intent and not by nature.
Nevertheless, the principle of every human action is natural. For although the conclusions of the theoretical and practical sciences are not naturally known, but rather are discovered through reasoning, nevertheless the first indemonstrable principles are naturally known, and from them we come to know other things. In the same way, the desire for the ultimate goal, happiness, is natural to humans, as is the aversion toward unhappiness. Thus, the desire for things other than what constitute happiness is not natural. The desire for these other things proceeds from the desire of the ultimate goal. For the goal in acts of desire is just like the indemonstrable principles in acts of the intellect, as is said in the second book of Physics (200a15-25). And so even though the movements of all the other parts of the body are caused by the heart, as the Philosopher proves in On the Motion of Animals (703a14), these movements can still be voluntary, while the first movement, that of the heart, is natural.
Moreover, let us recall that an upward motion is natural to fire as a result of its form, and hence that what generates fire, giving it its form, is essentially a place-to-place mover. In addition, just as a natural motion can result from the form of an element in a natural object, so also nothing prohibits other natural motions resulting from different forms in the same natural object. For example, we see that iron naturally moves toward a magnet, which motion is not natural to it as something heavy, but as something having a particular kind of form. In the same way, therefore, insofar as the animal has a particular kind of form, namely the soul, nothing prohibits it from having a natural motion as a result of that form. And the cause responsible for this motion would be what gives the form.
I myself say that the motion of the heart is a natural motion of the animal. As the Philosopher says in On the Motion of Animals, "We should consider the animal as if it was a city under good and legitimate governance. For in a city with this kind of stability of order, there is no need for a separate ruler for each and every event, but instead everyone does everything as planned, and things proceed according to custom. The same thing happens in animals naturally. For every part of the animal is naturally equipped to perform its own special function, so that there is no need for a soul in each and every part as a cause of motion. Rather, with the soul present in the principle of the body, the other parts live and perform their own special work as nature made them."
Thus, the motion of the heart is a natural result of the soul, the form of the living body and principally of the heart.
Perhaps this is why some who have understood this go on to say that the heart's movement is caused by an intelligence, for they think that the soul comes from an intelligence (which is similar to what the Philosopher says in Physics Book 8 [255b31-256a3]) about the movement of heavy and light things coming from a generator that gives the form which is the principle of their motion). But it is important to note that every property and movement is a result of a form in a particular condition. So as a result of the form of a subtle element like fire, there is motion to a subtle place, namely upwards motion. Now the most subtle form on earth is the soul, which is most like the principle of the motion of the heavens. Thus, the motion that results from the soul is most like the motion of the heavens. In other words, the heart moves in the animal as the heavenly bodies move in the cosmos.
Nevertheless the heart's motion is not exactly like the heavens', in the same way that what follows from a principle is never exactly like the principle itself. Now as the principle of all the motions in the universe, the motion of the heavens is circular and continuous. For the approach and departure of a heavenly body coordinates with the beginning and end of existence, and by its own continuous movement it preserves the order among moving things that do not exist forever. The motion of the heart, however, is the principle of all movements in the animal. This is why the Philosopher says in the third book of On the Parts of Animals, "the movements of pleasure and pain and of all the senses seems to arise there," namely in the heart, and they also end there. Thus, in order for the heart to be the beginning and end of all motions in the animal, it had to have a movement that is like a circle, but not exactly circular, composed namely from a push and pull. And so the Philosopher says in the third book of On the Soul, "A natural and organic cause of motion is both the source and termination of the motion. Now since all things are moved by pushes and pulls, it is necessary that something exists in a nearly circular state and that motion arises from it.
We can also say it is a continuous movement as long as the animal lives, unless it is necessary to have a rest in between the push and pull (for it is not a perfectly circular motion).
We are now in a good position to consider objections to the contrary.
For we see that the heart's motion is not natural to it as something having weight, but insofar as it is animated by a particular kind of soul. Moreover, the two motions that make up the complex movement of the heart seem contrary because the heart does not perfectly have the simplicity of circular motion, but it does imitate that motion since where it moves from it also moves toward. Thus, it is not problematic that its motion is in some way to different parts, for even circular motion is like this.
Next, there is no need to say that the heart's motion arises from either sensing or desiring, although it does arise from the sensitive soul. For the heart is not caused to move by the sensitive soul's activities, but insofar as that soul is the form and nature of a particular kind of body.
On the other hand, the progressive motion of an animal is caused by the activities of sensing and desiring. This is why doctors distinguish vital functions from animal functions and say that even when the animal functions cease, the vitals may remain. They call the vitals those functions that are immediately related to the heart's motion, such that when they cease life ceases. This position is reasonable. For to live for living beings is to exist, as is said in the second book of On the Soul: the existence of anything is from its own form.
We should note that there is a difference between the principle of the heavenly motion and the soul. The former is not moved in any way at all, neither essentially nor incidentally, but the sensitive soul, although unmoved essentially, is moved incidentally. Thus, different types of sensations and emotions arise in it. So, whereas the heavenly movement is always uniform, the heart's movement varies according to the different emotions and sensations of the soul. For the sensations of the soul are not caused by changes in the heart, but just the opposite is the case. This is why in the passions of the soul, such as anger, there is a formal part that pertains to a feeling, which in this example would be the desire for vengeance. And there is a material part that pertains to the heart's motion, which in the example would be the blood enkindled around the heart.
But in the things of nature, the form is not the result of the matter, but on the contrary, as is evident in the second book of Physics, matter has a disposition for form. Therefore, although someone does not desire revenge because his blood is burning around the heart, he is more prone to become angry because of it. But actually being angry is from the desire for vengeance.
Now although some change occurs in the heart's motion because of different sensations and feelings, nevertheless such change is involuntary, for it does not come about through the command of the will. For as the Philosopher says in On the Cause of the Motion of Animals, often something will be seen which, without any command of the mind, moves the heart and private parts, the cause of which he says is the natural susceptibility animals have to physical changes. For when its parts undergo change, one part increasing and another decreasing, then naturally the whole animal moves and goes through a sequence of changes.
Now warmth and cold, whether from the outside or occurring naturally within, cause such motions of the heart and private parts in animals, even against reason, by yet another incidental change. For the mind and imagination can cause a feeling of lust or anger or other passions, on account of which the heart is heated or cooled.
And let this be enough said on the motion of the heart.