The basic notions of Aristotle's philosophy of nature can be understood from his analysis of change. When Aristotle undertook to explain how it is that things change, a fact apparent to anyone, he had first to confront the seemingly iron-clad logic of Parmenides. Bound by this logic, Parmenides had been forced to the position that there is in reality no change at all. All change is mere appearance; reality is One, and this One, which only is, is unchanging. He was forced to this position because, as he understood the terms of the problem, change is logically not possible. Not having the notion of potency, Parmenides had argued that there are only two alternatives for anything, being and non-being. No new being can come from non-being since "nothing comes from nothing." Nor can new being come from being since what has being, already is and does not begin to be: "being cannot come from being since it is already."The advance that Aristotle made over Parmenides consists in seeing that, although it is true that "nothing can come from nothing," it is not entirely true that "being cannot come from being." One must distinguish being-in-act from being-in-potency. While it is true that from being-in-act, being-in-act cannot come since it would already be. The alternative from which being can come is not non-being, but being-in-potency. From being-in- potency there can come being-in-act.
Michelangelo is alleged to have said that when he set out to sculpt a statue from a formless block of marble, he sought only to remove the excess marble from the statue that was already there inside the block. This sentiment expresses what Aristotle discovered to be necessarily true for all change.
Aristotle discovered the concept of potency by observing accidental changes. He observed, for instance, that a sculptor can make a statue from a block of marble. This is possible only because the block of marble is endowed with
a certain property - the possibility and capacity of being transformed. The figure of the statue is in potency in the block of marble. This potency is not nothing, it is not non-being. It is real; not with the reality of being-in-act, but with the reality which corresponds to being-in- potency.
The first principles of motion can be discovered but they cannot be demonstrated. In order to demonstrate them,
we would have to assume that they are the result of other principles, in which case they would not be the first principles. These principles are not demonstrated but discovered by analyzing substantial changes.
In his analysis of change, Aristotle discovered that every change implies duality. It implies a subject in potency which, by the action of some agent, passes into act, i.e. receives some new perfection or actuality. Motion presupposes the acquisition of something and the corruption of something else. The subject of change is what stays the same through the change. However, through the change, it acquires something new and loses what it previously had. Motion implies a passive principle and an active principle, intrinsic to the thing that changes.
Thus, there are three principles necessary for change to take place. There must be something new that comes to be, something old that passes away, and something that stays the same throughout. In the Aristotelian tradition, these principles receive the names form, privation and matter. Form is what comes to be, privation is what passes away and matter is what stays the same throughout the change. In the case of a statue, the shape of the sculpture, Michelangelo's "David" for instance, is the form that comes to be when a formless block of marble becomes a statue. The formlessness of the block is itself the privation of the statue shape, and the potency for the statue shape. The marble, first in block shape, later in "David" shape, is what stays the same throughout the change. The case of the coming to be of a statue is an instance of an accidental change; what changes are the accidents of the marble. What stays the same is the substance of the marble.
For Aristotle, motion is the technical name for changes in accidents. There are three kinds of motion for Aristotle: a change in quality (which he calls alteration), a change in quantity, size (called growth or diminution), and a change in place (called local motion). In all cases, motion, as such, is defined as:-
the act of a being in potency insofar as it is in potency.
Motion is the process that a substance goes through in which it loses one accidental form or actuality and gains another. As such, motion is an actuality, but an imperfect one. Hence, the definition includes the qualification "insofar as it is in potency." Motion is the act of something that does not yet have, but is acquiring, the full act of a new accidental determination, a new quality, size or position. While the motion is taking place, the new determination is neither fully actual (for then the motion would be over) nor fully potential (for then the motion would not have begun.) The fact that motion is an imperfect act implies, for Aquinas, that for every true motion, there must be a cause sustaining that motion.
Aristotle discovered these principles of nature (matter, form and privation) by analyzing accidental changes. He found that they could also explain the more fundamental kinds of changes, changes that involve the passing away and coming to be of substances.
In order to find an example of a substantial change, i.e. a change that involves the coming to be or passing away of a substance, one first has to admit that there are substances of different kinds. For example, if one admits that sodium and chlorine are different substances (and they certainly appear different - one is a white metal, the other a green gas), and that they are each different from salt (also apparently so), then one can see that the change from sodium and chlorine to salt is a substantial change. The Aristotelian principles used to explain the change are the analogous to those used in explaining accidental changes: matter, form and privation. What comes to be is a new form in the matter, i.e. in what persists through the change. This new form comes to be in what previous lacked that form, i.e. in what had the privation of the form. Thus, the form salt comes to be in the matter of chlorine and sodium. Form and matter, however, make up a substantial unity; one cannot have form without matter, nor matter without some form. But, one can still distinguish these principles, and also understand that these principles are real features of the things that exhibit them.
Modern science has pretty well confirmed atomic theory as an explanation of chemical reactions. Thus, it is sometimes thought that this theory supercedes Aristotle's hylomorphic theory. Material things, then, are thought to be fully explained as the collection of atoms, united into molecules of varying size and complexity. Macroscopic objects, like trees and animals and planets, are thus seen to be the collection of so many parts, much like a machine, that work together in a kind of harmony. If Aristotle's thought is to be assimilable to modern atomic theory at all, it is sometimes proposed that his notion of form simply designates the arrangement of smaller parts, say atoms or molecules.
However, to say that the form is the configuration of parts, does not capture all that Aristotle means by form. While it is true that there can be no form without matter, and in a certain sense, form is realized in matter in a certain configuration, the matter all by itself does not account for its configuration. A favorite example of Aristotle's is the case of a house made out of bricks. The bricks are the matter of the house, but bricks all by themselves do not account for the house, as opposed to a pile of bricks. The form is a cause in the sense of that it is constitutive of the thing it is the form of, just as the matter is constitutive of the thing. But form has a certain priority and explanatory value because the form accounts for the matter being in a certain configuration while in that configuration, something that matter cannot do.
Thus, to claim that atomic theory explains all of the phenomena of observation is simply to miss some observations, or to suppose that more is explained than actually is. Richard Connell in Substance and Modern Science (Houston: Center for Thomistic Studies, 1988) puts the point well :- Reflecting on the theory, we see that the representation of atoms as aggregates does account for the union and separation of atoms, but that it does not explain the disappearance of some properties and the coming to be of others, except for adding the mass (mass-energy), which is conserved. (We might add the that total charge is conserved too.) So given that changes have occurred in almost all the properties, we know that something more than a mere uniting must occur, even though the nature of the additional activities or interactions is left in the dark. That some sort of interaction must occur cannot be doubted, if observation is to mean anything, but precisely what the character of the interaction is we have no way of determining.
© Joseph M. Magee