MOTION, FIRST CAUSE OF

Experience shows that some things in the world are in motion, whereas others are at rest, and that things pass from rest to motion and from motion to rest. In view of these facts, the question arises whether each and every thing is so constituted as to be capable of both motion and rest, capable of being either a mover or something moved, or whether besides things of this sort, something exists that is a mover, but is itself unmoved by any other. Is there an unmoved mover that is the primal source or first cause of motion? Scholastic philosophers commonly answer this question in the affirmative.

Existence of an Unmoved Mover

The scholastic proofs for the existence of a first unmoved mover are based upon an argument first proposed by aristotle (Phys. 241b 24–267b 27) and subsequently commented upon by St. thomas aquinas (In 7 phys. 1–9; In 8 phys. 1–23) in the context of their natural philosophy. In what follows, the concepts and distinctions presupposed to this argument are first explained, then the argument itself is exposed, and some observations made on the place of such a proof in natural philosophy and its relevance to traditional proofs for the existence of God.

Presuppositions. By motion is meant the act or process of change. This is not a disembodied energy, nor something purely and simply actual, but an actual determination of a natural body precisely as this is capable of further actuation. Motion thus conceived requires a mobile or potential subject that remains the self-same throughout the change, but becomes different from the way in which it was before the change. When a body passes from rest to motion, motion itself begins to be in this mobile subject. Whatever begins to be does not spring from mere nothing, nor does it produce itself, but depends for its being on some active principle, called the efficient cause. The efficient cause is the mover, or active source of motion, whereas motion is an effect produced in the moved or mobile subject. Each kind of motion requires a mobile subject capable of being moved with that motion, as well as a mover able to produce the motion.

Atemporal Aspect. If the supposition is made that motion had a beginning in time and has not existed from eternity, then it is manifest that there must be a first efficient cause of motion, because anything that begins to be requires an efficient cause from which it originates. However, since it is not clear from human experience or scientific reasoning that motion did have a beginning in time, the present discussion does not assume this.

Accidental vs. Essential. In order to prove by reasoning that there is a first cause of motion, a distinction should be made between motion that is caused or possessed accidentally and motion that is caused or possessed essentially. Motion is accidental when it is associated with something that merely belongs to something moved, as a color belongs to an animal and is moved accidentally when the animal moves. Motion is also accidental to something contained as a part in a whole; when the whole is moved, the part shares the motion of the whole, as a man in a boat is moved with the boat. On the other hand, motion is essential to something that is moved of itself, and not merely as part of another. Thus the motion of a stick moved by the hand, or of a thrown stone, is essential motion. Accidental motion presupposes and requires essential motion, and to the latter the argument is confined.

Mover and Moved. Several conditions must be fulfilled in order for essential motion to occur. First of all there must be a distinction between the mover and the moved: whatever is moved is moved by something else. The distinction between the mover and the moved appears by way of induction from sensory experience, and by reasoning from effect to cause. Among the things that have essential motion, some derive their motion from themselves, and others from something else; in some cases the motion is natural, whereas in other cases it is mechanical, that is, by impressed force.

It is manifest that things moved mechanically, by art or by violence, are moved by something else, that is, by a mover distinct from the moved. On the other hand, living things have in themselves an active principle or efficient cause of their own motion, by which they move themselves in different ways. They are also composed of heterogeneous parts; the part that causes motion is distinct from the part moved, as the nerves and muscles are distinct from the bones. Organisms thus move themselves by means of their parts, with the part in motion being moved by another part that is an active cause of motion. Nonliving bodies do not appear to move themselves, or to have in themselves an efficient cause of their own motion; thus they are moved by some cause that is distinct from themselves.

Reason also aids in understanding that whatever is in motion is moved by something else. Motion itself is an effect requiring both an efficient cause and a subject capable of being moved. If something is in motion and does not have the efficient cause of its motion within itself, then it is moved by something other than itself. If it does have the cause of motion within itself, then it moves itself by means of its parts, and these are related as mover and moved. In all cases, whatever is in motion is divisible and has parts, and the whole depends upon the parts, both for its existence and for its motion, whether it is moved by something else or moves itself.

Contact and Simultaneity. The second condition required for motion is that the mover and the moved must be together. Experience shows that some things are capable of causing motion and yet sometimes are not causing it, and that some things are capable of motion, but sometimes are at rest. Motion requires not only a distinction between the mover and the moved, but also that mover and moved be together in place and time. The need for contact between the mover and the moved may be understood inductively, by considering the various kinds of motion, whether according to place or quality or quantity, and by reasoning in terms of cause and effect.

Local Motion. In regard to local motion, everything that is moved locally is moved either by itself or by something else. Something that moves itself has the cause of motion in itself, and so in this case it is clear that the mover and the moved are together as parts of one and the same whole. A body can be moved locally by something else in various ways, namely, by pushing, pulling, carrying, etc. Yet all these are reducible to some kind of combining or separating, because by local motion things are either brought together or separated.

Both experience and reason show that combining or separating require contact between the mover and the moved. The reason lies in the fact that the mover is the principle and cause from which the motion proceeds and begins to exist in the moved. Without contact the mover would have nothing on which to act. Since mover and moved are together and, as it were, one by contact, they share one and the same motion in different ways: the mover as efficient cause and the moved as patient or subject. Just as an effect cannot come from nothing, so it cannot come to be without some contact with its source. (see action at a distance.)

Alteration and Augmentation. In cases of change in quality, whatever causes alteration and whatever is altered are in contact with each other. This is clear in regard to sensory qualities and the organs of sense. For sensations of touch, taste, or smell to take place, something with the peculiar sensible quality must contact the proper organ of sense to act on it and cause the sensation, which is a kind of alteration. Sight and hearing also require contact with the appropriate sense, although in these cases the distant object first causes an alteration in the medium, and then, through the medium, causes an alteration in the sense. Likewise, when the condition of contact is fulfilled, natural bodies interact through their physical and chemical qualities and cause alterations in each other. In change of quantity also, whether increase or decrease, there is contact between the organism and the parts that are added or lost.

Together in Time. Furthermore, mover and moved are together in time as well as in place; that is, they are simultaneous. At the same time as the mover causes motion, the moved is in motion. This is seen in the example of the hand moving the pen. The motion of the pen requires the hand as mover and contact of the hand with the pen; when, and only when the hand moves the pen, the pen is moved by the hand. Mover and moved are together in place and time because they are parts of one system, and the motion is the act of both mover and moved, although in different ways: it is actively from the mover and passively in the moved (see action and passion).

Argument for a First Cause. Although man has no experimental knowledge of the prime mover, he can reason from sensible effects to the first cause of motion. It is evident from experience that something can be moved by something else in two ways. The proximate mover may itself be the source of motion, or this mover may depend upon something else. A mover that is itself the source of motion may cause the motion either directly and immediately, or through one or more intermediates, as a man can move a stone either immediately or by means of a stick in his hand. In such a case the stone is moved principally by the man, and only instrumentally by the stick, because the man moves the stick, but the stick does not move the man, nor does it move the stone unless it is moved by the man.

With facts and distinctions such as these in mind, one can propose a general argument. Many things in the world are in motion, but everything in motion is moved by something else, and mover and moved are together in place and time. The mover, in turn, is either moved by something else or it is not. In either case there must be a first mover that is not moved by anything else, but is itself as unmoved mover and the first cause of motion. Motion requires an efficient cause, and every cause that is a moved mover requires another efficient cause. Every moved mover, regardless of how many there may be in any given series, is an intermediate cause dependent upon another cause. Such a series of movers moved by something else cannot be infinite, but must terminate in a first cause of motion that is not moved by any other. If there were no unmoved mover, there would be no first cause of motion nor any other cause, and hence no motion, which is contrary to fact.

This argument may be stated briefly in another way. Where there is motion, there must be a moved and a mover, distinct and yet together in place and time. There may also be an intermediate mover or instrument of motion. Motion is in the moved; the intermediate mover moves something and is moved by something; there must also be a first cause of motion that is unmoved by anything else, because the effect cannot be without such a cause. If anything is a mover and yet incapable of causing motion by itself, but only as moved by something else, and this in turn by something else, then such a series of moved movers cannot be infinite. It must be limited, in the sense that an unmoved mover must be the first cause of motion. Besides all the movers moved by something else, however many they may be, or of whatever kind, there must be a first cause of motion that imparts motion by itself and is an unmoved mover, independent of every other.

Role in Natural Philosophy. Questions concerning the first cause of motion may arise either in natural philosophy, or in metaphysics, or in natural and sacred theology. In natural philosophy the first cause of motion is considered only insofar as is necessary to understand motion in natural things and to determine whether the primary source of motion is or is not a natural body (see philosophy of nature). A body is something extended and divisible in parts that are in it and thus compose the whole. A body or extended whole is not an independent being, but depends upon its own parts for its being. A body is dependent upon its parts for being moved, because motion requires a subject that is extended and divisible into parts, but the first cause of motion is completely independent in action, and hence also in being, because operation follows being, and the manner of acting is consequent upon the manner of being. Therefore, the first cause of motion is not a body, and does not have parts on which it depends for its being and acting. It is not composed of matter and form, nor of potency and act. It is not capable of being moved or having motion, either by itself or by something else, but is the unmoved mover of other things. Because it is unmoved, it is not a temporal being but eternal. Because it is unmoved and incorporeal, it does not cause motion mechanically, as one body moves another from without, but rather as mind or intelligence moves a body with a higher order of action. It may be true that there are many kinds of spiritual beings who are intermediate movers, in the sense that they cause motion only insofar as they are themselves moved by another mover in a way different from the movements to which material things are subject. If this is the case, however, these spiritual beings are not the first cause of motion whose existence has been proved, but are themselves moved by it.

To account for motion in the world, it is sufficient for the purposes of natural philosophy to admit one first cause of motion. One mover entirely unmoved suffices to cause motion in all things that are moved—not indeed as the only mover, but as the only first and unmoved mover—because it acts with complete independence, whereas everything that is moved in any way whatever is dependent upon an unmoved mover. Moreover, the first cause of motion is eternal and acts without detriment to itself, and so is capable of being the first cause of all motions in the world. Furthermore, the unity and the order of the world indicate that the first cause of motion is one and unique, somewhat as the orderly motion of an army indicates that there is one in command (see universe, order of). To treat of the first cause more profoundly and in greater detail pertains to metaphysics and theology (see god, proofs for the existence of).

First Mover and God. It is sometimes questioned whether the first cause of motion proved in natural philosophy is the being whom men call God, and whether the existence of God can be discussed or proved with the concepts and principles that pertain to natural philosophy. Although the considerations of this branch of philosophy are limited, and the first cause of motion is not included within the proper subject of natural science, yet Aristotle touched upon these ultimate problems in his Physics, and both St. Thomas Aquinas and Sir Isaac Newton maintained that in natural science one should seek the first cause of motion, and treat of God inasmuch as He can be known as the cause of motion in the world. Moreover, as has been shown in the argument above, one can prove the existence of the first cause of motion through the data of experience and the principles of ordinary understanding and can show that this cause is not a natural body but an incorporeal and unmoved mover, entirely independent in action and being, and so reasonably identified with the being that men call God.

This proof from matter and motion, suggested by Aristotle and pursued by St. Thomas, has many advantages. From ordinary experience and consciousness men are aware not only of sensible motions in the world, but also of activities such as sensation, thought, and volition in themselves. Although these last are not motions in the strict sense of the term, nevertheless they are motions in the broad sense of alterations or qualitative dispositions. Sensations are initiated by sensible motions, and thoughts and volitions are in some ways dependent upon sensible motions, as they are also causes of sensible motion in man and in other things. Even thoughts and volitions are dependent on a first cause of motion, because every passing from potency to act requires a mover and ultimately an unmoved mover. It is the proper business of the natural philosopher to seek the causes of motion in natural bodies, and in order to understand his subject he must not rest content with some intermediate mover, nor with all intermediate movers—supposing that they could all be determined—but must seek the first cause of motion. Furthermore, it is only after one knows, through the study of nature, that there exists a kind of being that is not mobile or corporeal, but immobile and incorporeal (including the unmoved mover and spiritual substances) and that he can show the need for a science, beyond natural philosophy, called metaphysics (see being).

See Also: god; efficient causality.

Bibliography: e. a. sillem, Ways of Thinking About God (New York 1961). v. e. smith, General Science of Nature (Milwaukee 1958). w. a. wallace, "Newtonian Antinomies against the Prima Via, " The Thomist 19 (1956) 151–192. m. j. adler, ed., The Great Ideas: A Syntopicon of Great Books of the Western World (Chicago 1952) 1:179–192, 543–604.

[w. h. kane]