NATURE AND MOTION

INTRODUCTION

            Natural things are either in motion or being in potency to move. Things in motion can be defined only in the contrary of potency and act. Since nature is composed of a multiplicity of things, Aristotle defines nature as a principle of motion and change.[1] This implies that motion is the basic property of natural things. Thus, there exists an intrinsic relationship between nature and motion. It therefore follows that, for an accurate understanding of nature, a similarly accurate understanding of motion and its species is imperative and indispensable.

            In view of this, we shall attempt an analysis of motion and its species from an Aristotelian point of view. To achieve this, we shall begin with a definition of nature and then motion; afterwards, we shall look at necessary factors for motion. We shall further elucidate the term motion “per se” and “per accidens”, next we shall consider the kinds of “per se” motion while analysing the species of motion. Thereafter, we shall examine the contrariety of rest and motion, then, its modern application.

DEFINITION OF NATURE

            Nature according to Aristotle is an inner principle or the source and cause of being moved or being at rest per se and not per accidens.[2]  This means that nature is that in which it belongs primarily and not in virtue of concomitant attributes.

            Some people conceived nature as matter considering it as the subject and constitutive part of natural things but this idea is false if matter is considered as the whole substance. Others consider nature as form because the actual thing does not come into being until it receives a certain form. It is the form that gives the thing identity and actuality. But since the identity of a thing comes more from its act than from its potency, nature applies more to the form than to the matter even though both are nature.

DEFINITION OF MOTION

            Since natural things are either in motion or at rest and such things in motion can only be defined in potency and act, Aristotle condemned the definition of motion by some people. One of such definitions is that motion is “a going out from potency to act which is not sudden.”[3] This definition is erroneous because elements that are posterior to motion have been included. “Going out” (local motion) is a species of motion which comes after motion. Similarly, “sudden” involves time in its definition, since sudden is an occurrence in the indivisible time (that is, the instant).[4]

            Some philosophers assert that act and potency are prior to motion; thus, they cannot be used to define motion, since it is impossible to define motion in terms of what is prior. On the contrary, Aristotle uses these to define motion. Thus, he posits three working definitions of motion.

            First, motion is defined as the fulfilment of what exists in potency, in so far as it exists in potency.[5] Thus, it is neither the potency of a thing existing in potency for some things are actually in potency, nor the act of a thing in act. Rather, it is the act of a thing in potency where the word “act” designates its relation to a prior potency and the words “of a thing in potency” designate its relation to a further act. By this definition three implications can be drawn.

            The first is that motion is an incomplete act. Again, things in potency tend towards actuality. This is made possible by the movement of such a thing. We shall buttress our point with the analogy of a building. When the building plan is drawn, we can say that it is in potency, with the actual building started, motion begins. Thus, the construction of a building has already begun and is partly in act; we say that a house is being built.

Again, to state that motion is the act of a thing in potency implies that as an act, motion is found in its proper subject, which is something in potency. Hence, all bodily things are in act and in potency in different sense, and they subject to the motion of one another. Thus, they both act and are acted upon.

            Furthermore, the phrase in so far as it is in potency is necessary because the act of something in potency can be static. The act is in motion only in so far as the subject is capable of further act. Thus, the shape of a half carved statue is not in motion unless it is the shape of the wood in so far as the wood is capable of further form.[6]

            Second, motion is defined as “the fulfilment of the mobile in as much as it is mobile.”[7] This definition is a conclusion to the previous one. Since motion is the act of what exist in potency, in so far as it exist in potency, and we know that whatever is in potency is mobile and not the mover (for the mover as such is in act), it follows that motion is the act of the mobile as such. Aristotle in his physics buttresses this definition with the analogy of the bronze. He asserts that “bronze is potentially a statue. But it is not the fulfilment of bronze as bronze which is motion. For ‘to be bronze’ and ‘to be a certain potentiality’ are not the same”[8] This denote that it is not the actualization of bronze as bronze that is motion, rather, it is the act of the potentially existing bronze in transition to a statue.

            In the third instance, motion is defined as the fulfilment or transition of a thing from one point (real and imagined) to another, either from its qualitative, quantitative, substantial or spatial form. This possibility of natural things to change is grounded in the principle of nature (form, matter and privation), efficient causality and final causality. Hence, to set a thing in motion implies causing it to transit from potency to act. The implication of this is that only things in act can bring others from potentiality to actuality. Consequently, motion is as such necessarily contingent upon a subject’s lack of a certain form (privation) which it is capable of receiving and an agent possessing the perfection it is about to produce.

            It is pertinent to note that that which has the power of causing motion can only act in reference to the thing capable of being changed, and that which is capable of being changed can only suffer change under the action of that which has the power to change it. Hence, motion cannot exist apart from what moves, for there is no such thing as motion in abstract. Again, motion is action in the mover and passion in the moved. Action and passion are motion. The mover (action) is also moved, this is because the mover sets the subject (passion) into motion by contact. Thus, being acted upon also.[9]

NECESSARY FACTORS FOR MOTION

            Things in the world are in motion. As earlier stated, motion is the basic property of physical things. Accordingly, for motion to be possible, certain factors ought to be responsible. Aristotle posits five factors responsible for motion. These include:

1.      That which directly causes motion. This we term efficient cause or the mover.

2.      That which is in motion (the mobile or subject of the motion)

3.      That in which motion takes place, namely time.

4.      A starting point or terminal of the motion.

5.      That to which motion proceeds (the end point or terminal of the motion), since every motion proceeds from something to something.

That which is directly in motion (that which is being moved per se) is distinct from that to which it is in motion and that from which it is in motion (both terminals). For instance, let us consider these three things heat, hot and cold.  The cold water is being heated; in this sense, it is neither cold nor hot, but somewhere in between, tending towards heat. On the other hand, per accidens, the cold water (the privative starting point) becomes hot. Therefore, “any change is named after its destination because the final terminal (terminus ad quem) specifies a motion”[10]

MOTION PER SE AND PER ACCIDENS

            Things that change do so in two senses:

1.      Per Accidens: A thing is said without qualification to change because something belonging to it changes (a change in the part affects the whole), e.g., the body is restored to health because the eye is restored to health.

2.      Per Se: The case of a thing which is in motion neither accidentally nor in respect of something else belonging to it, but in virtue of being itself directly in motion.

Having stated the facts above, we shall concern ourselves with motion per se and per accidens. To elucidate our point, we shall consider the mobile (the moved) and the mover. Accidental and essential motion may be exemplified from the perspective of the mobile thus; when we say that a nurse is dancing. The person who is dancing is the proper subject, who happens to be a nurse (an accident), and she is not dancing because she is a nurse. Per se motion in this case, is the one ascribed to a subject as properly and as a whole.[11] Similarly, the same distinction can also be made from the perspective of the mover applying the same example; the nurse is piloting (accidental) and the nurse is nursing (per se).

THE KINDS OF PER SE MOTION

Per se motion is one which is not accidental, for accidental motion may be found in everything and in any respect, but per se motion is found only in contraries.[12] Aristotle proceeds to point out that change with respects to its terminals (starting and ending) is from:

1.      A non subject to a subject (this occurs between contradictories and is called generation). A vivid example is change from sperm to man.

2.      A subject to a non-subject (this is also contradictory terminals and is called corruption), such as being to non-being (death)

3.      A subject to subject.

Change from non-subject to a subject is not motion because non-subject does not exist and cannot be moved, and as non-existent, it has no terminals or contraries. Hence, it is devoid of a place. In Aristotle, this argument could also be applied to prove that change from a subject to a non-subject (corruption) is not motion, since both generation and corruption are instantaneous whereas, motion is continuous. Motion in the strict sense occurs in the change from subject to subject (from being to being). This is because, the two subjects signify two affirmative contraries (terminals), for instance, motion from white to black. Thus, with the knowledge on the terminals, we shall proceed to discuss the species of motion.

SPECIES OF MOTION

            Having established the fact that motion in its strict sense occurs from being to being, Aristotle identifies three species of motion; namely:

1.      Qualitative motion

2.      Quantitative motion

3.      Local motion (motion in respect of place or locomotion)[13]

However, to understand this clearly, it is pertinent to examine the ten categories paying special attention to the ones that admit motion.

            Since motion is defined in terms of terminals, as earlier stated, and these terminals are distinguished according to genera of the predicaments or categories, the species of motion must fall within these ten categories. The categories are: substance, quantity, quality, relation, place, time, position, state, action and passion.[14] Among these ten categories, only three admit of motion. These are: quantity, quality and place (location).[15] It is relevant to note that motion does not belong by full right to these categories, but it is placed in them by reduction.

            In respect of substance, there is no motion because motion is between contraries. Substance has no contrary; it has only contradictories, that is, non-substance (woman and non-woman). Likewise, time does not admit motion, because it is the measure of motion and a mental construct. There is no motion in relation. This is because there is the possibility to change without any motion in the subject, for instance, it is possible for Precious to grow to Frederick’s height without any change in Frederick. Again, there is no motion in respect of action and passion. That is, there can never be motion of mover and moved, because there cannot be motion of motion or becoming of becoming, etc. Aristotle argues that, as distinct categories, they do not admit of motion although used often to include motion.

            From the preceding paragraphs, we have been able to establish that continuity and contrary extremes of possible motion can only be found in categories such as: sensible qualities, quantities and place. Thus, there are three species of motion: qualitative motion, quantitative motion and locomotion. As earlier stated, because motion is an imperfect act, it does not belong to these categories as a full right but placed in them by reduction.

Qualitative Motion: Motion in respect of quality is called alteration (a general designation that is used to include both contraries). It could also be said to be motion in respect of sensible qualities. A vivid example is a change from white to black.

Quantitative Motion: This has to do with growth or decrease. There is a minimum quantity at which (the motion) of growing begins, and a maximum at which it is terminated. Motion in respect of quantity is called increase or decrease according as one or the other is designated; that is to say, motion in the direction of complete magnitude is increase while motion in the contrary direction is decrease.

Motion in respect of place (Locomotion): This may be designated by general name of locomotion. In other words, it is called local motion. It indicates change of place or location.[16]

CONTRIETY OF REST AND MOTION

            Contrary things differ from each other. Thus, “contrary motions are respectively from a contrary to the opposite contrary and from the latter to the former”[17] contraries are from the same genus, for example, white and black belong to the same genus of colour, tiger and goat to the genus of animal.

            Rest can be contrary to motion just as motion can be contrary to motion. This is possible because rest is a privation of motion in the things that are capable of motion. When we make reference to motion between a positive beginning and a positive ending, we consider it from a starting point to an ending point as a rest in the starting point. For example, the motion from disease to good health is rest in disease. Therefore, the contrary of a motion from good health to disease is rest in good health; that is because rest in the goal of motion is the consummation and perfection of that motion.[18] Hence, the rest was caused by motion, it therefore cannot act as its opposite simultaneously or in return.

            In like manner, in situation where two states of rest correspond to contrary motions, they (the states of rest) can be contrary. That is to say, two states of rest that are similar to opposing motions are opposing themselves. To buttress this, we can say that in situation whereby two states of rest correspond or become similar to two states of motion that are opposing to themselves, the two state of rest are in themselves opposed to each other. To get the impression that these two states of rest were not opposed to each other would have been in a situation where they correspond to similar motion.

            Discussing changes that do not involve different terminals, such as generation and corruption, opposition is based on approach and departure from the same terminal.[19] These changes are not regarded as motion, and as a result, have no state of rest, but non-change stands as the opposition of such change; that is, non-change in a non-being is opposed to change in regard to being just as non-change in a being is opposed to change in regard to non-being.[20] This opposition is similar to the one between opposing motions. The opposition corresponds to that between rest, and rest is non-change towards being (in a potential being) as opposed to non-change towards non-being in an actual being.[21]

MODERN APPLICATION OF MOTION

            Motion has been applied in varied fields of sciences. This is asserted by William Wallace in his book The Modelling of Nature. Among these are its use in Geography and Astronomy. It is used in these fields to discover revolution and evolution of the earth and other planetary bodies. Astronomers have also proved that the movement of the earth and the moon causes rise and fall of ocean tide.

            Modern day physics shall go into extinction without the application of motion. This is evident because certain phenomena support kinetic theory of matter and Sir Isaac Newton’s law of motion.  These include diffusion, plasmolysis and osmosis among others. Again, the first law of thermodynamics states that energy can neither be created nor destroyed but can be transformed from one form to another. This implies that energy involves a series of conversion from one form to another. This conversion involves a particular kind of motion. Given these, we can assert that motion is applicable in modern science.

CONCLUSION

            We have critically analyzed the idea of motion in the Aristotelian-Thomistic framework. This involved a definition of nature and motion. For motion to be possible there should be factors facilitating it, the mover, subject, place, and time, among others. Equally, there is a distinction between motion per se and motion per accidens. We also stated that there are three species of motion according to Aristotle (qualitative motion, quantitative motion and motion in respect of place) taken into cognizance the fact that motion exist between two contraries. We further considered the modern application of motion.

            From the forgoing, we can assert that motion occurs midway between things that are in act and in potency. Thus, it involves a relationship between extrinsic efficient cause and its object. Fundamentally, a thing that moves is moved by another which by virtue of that function must be an act.

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[1] Cf. Aristotle, Physics, Bk III, part 1.

[2] Cf. Ibid.

[3] Fr. Kenny’s note on Philosophy of Nature, p. 27.

[4] Cf. Ibid.

[5] Cf. Aristotle, Physics, loc. cit.

[6] Cf. Fr. Kenny’s note on Philosophy of Nature, p. 28.

[7] Ibid., p. 29.

[8] Aristotle, Physics, loc. cit.

[9] Cf. Aristotle, Physics, Bk III, part 2.

[10] Fr. Kenny’s note on St. Thomas Commentary on Aristotle’s Physica, p. 33.

[11] Cf. Ibid.

[12] Cf. Aristotle, Physics, loc. cit.

[13] Cf. Aristotle, Physics, Bk III, part 1.

[14]Cf.  Omoregbe J., A Simplified History of Western Philosophy (Lagos: Joja Press Ltd.), p. 50.

[15] Cf. St. Thomas, op. cit., p. 34.

[16] Cf. Aristotle, Physics, loc. cit.

[17] V. E. Smith, The General Science of Nature (Milwaukee: The Bruce Publishing Company, 1958), pp. 340 - 341

[18] Cf. Fr. Kenny’s note on Philosophy of Nature, p. 36.

[19] Cf. Ibid.

[20] Cf. Ibid.

[21] Cf. Ibid.