In any case, if my reasoning is correct, then in order to change, something has to be a body (or system of bodies, of course). This seems like the most reasonable candidate for change anyway, since it is a multiple unit, and so some of it can perdure, establishing the continuity between its past and its future, while ways in which it is organized can disappear and come into being.
Aristotle explained change in terms of "being in potency" and "being active(1)," where "being in potency" means "being deprived of" some activity (and so having an end outside it, in the sense of outside the state it is in at the moment), while being active means "possessing its end within it," in the sense that it is then in the state that would be expected of it (or is doing what its internal structure demands for it)(2).
But what on earth is the "privation" of the act, which is the "privation" of a definite act and is not simple finiteness? That is, if you heat wood, then at some point (the combustion heat) it is "deprived" of the act of ashes and carbon dioxide and so on--and of no other act whatever (it is not "deprived" of being a horse). Well, it needs to be the products of combustion now. Yes, but what is it in its structure that is this "need"?
This Aristotle does not really address, and with his notion of "matter" as "stuff," I suppose he didn't really have to; though it is a little odd that matter as "potency" for being what it actually is doing can somehow be "potency" for doing something else while it isn't actually doing that something else. That is when the being is in potency, by the way in Aristotle. When your matter is the ability to be what you are, then it is "potency" to be you, but you are not "in potency" to be what you are.
In any case, Aristotle's view of what being "in potency" is is a little vague, to say the least(3).
So here is what I think is going on, expressed in a couple of definitions.
Equilibrium is the condition of a body in which its unifying energy has the quantity that it can exist with, and consequently it is the condition of a body in which its total energy is what can be "expected" of it based on the amount of its unifying energy.
Immediately, we can draw the following conclusion:
Conclusion 3: A body in equilibrium will stay that way if left to itself.
Actually, it is the "staying that way" that is what the physicists and chemists think of when they talk of "equilibrium"; but since the term means "being in balance," then obviously the tendency to remain in equilibrium is a characteristic of what is in equilibrium rather than the definition of it. To define equilibrium as "staying as it is" is another one of those instances like defining "death" as "cessation of brain activity" and taking a property as the essence.
But it is clear that staying as it is will be what happens when something is in equilibrium, because there is nothing internal that would get it out of its condition.
Note that what I said in the preceding chapter makes sense out of this characteristic of equilibrium in inanimate bodies. Since their equilibrium is the minimum energy-level they can have as the particular kind of body in question, and since their only spontaneous tendency to change involves a tendency to lose energy, then at their lowest energy-level, there is nothing they can do except stay the same.
I hasten to reiterate, however, that this does not mean that the body is inactive. Equilibrium is precisely activity, but stable activity. That is, in an atom, for instance, in its ground state, there is activity going on between the protons and the electrons, which can be considered as a constant kind of "exchange" of energy (and can even be expressed as an exchange of particles) among them. But this "tossing back and forth" happens in such a way that for every "particle" that goes one way there is one going the other way, or for every loss there is a corresponding gain; and so no change is taking place, really; there is no difference, though there is doing.
There may, therefore, be acts that look like changes, but are in fact acts in equilibrium. How do you tell the difference?
Conclusion 4: A body in equilibrium will not either gain or lose energy.
If the energy level remains the same, then the body is simply being active; it only changes when there is either a net gain in it afterwards or a net loss. This, as we will see, is also true when the body becomes a different kind of body or even a multiplicity of bodies, as when you burn wood and it turns into carbon dioxide, water, and ashes. These products of combustion have a different energy-level from the wood as it existed at the beginning of the change (as can be seen from the heat given off as "free"--wasted--energy).
However, any "change" which is cyclic, where the body which is "changing" returns exactly to its original condition, and where this cycle keeps repeating itself, is not a change at all, but an activity in equilibrium. It seems to be a change, because within the cycle, it looks as if there is a loss or gain of energy; but the energy is being traded off within the system (which is, of course, a unit) and so is maintained in the system, as can be seen from the fact that the part that lost the energy regains it in the course of the cycle.
Thus, "changes" which can be expressed by sine curves in physics are actually acts in equilibrium, not change.
However, if the sine curve has what they call an "envelope" in which the amplitude diminishes, then a real change is going on, because energy is being lost or gained. The "envelope" is the real change, and the sine curve expresses the internal activity that is doing the job of getting rid of the energy in the way expressed by the envelope.
For practical purposes, systems in the "real world," as they say, always act in sine curves with envelopes, for the reason that a system is an interconnection of bodies acting on each other, which means that each is doing work; and in doing work, as the Second Law of Thermodynamics says, some energy is lost out of the system.
Thus, it is only the "perfect" pendulum which swings back exactly to where it was when it started; but any real pendulum will lose energy because of friction at the point at which it is suspended, friction against the air as it moves, and so on--which, of course, is why you have to wind your grandfather clock, even though so little energy is lost that it goes on for days on a winding.
Similarly, the earth-moon system is slowing down the rotation of the earth because of the pull backwards by the revolving moon, while at the same time the earth is making the revolution of the moon speed up a bit, which brings it into an orbit closer to the earth, and so on; so even though it seems as if the planetary bodies are moving in perfectly cyclical orbits, this is not actually so; they are not at their lowest energy-level, and are actually adjusting themselves downward, imperceptibly, millennium by millennium.
On this point, Newton's First Law of Motion (that a body at rest will remain at rest or one in motion will keep moving in a straight line at a constant speed) is one of those abstractions like the "perfect pendulum." It is supposedly what would happen if the body were not acted on by any force whatever from any other body; but in the real world, this would mean that no other body could exert a gravitational or electrical or other pull on it, which in turn would mean (as we saw when discussing position) that it would be nowhere--in which case, as we will see, it becomes meaningless to say that it is moving.
But that aside, Newton's First Law does not apply in the real world, because every body is subject to many forces. Newton got it from noticing that the more you reduce the effect of these forces (insofar as you are able) the more a moving body tends to maintain its speed and direction. But of course this can only be tested by using horizontal motion on the earth, because you can't get rid of earth's gravity, which is significant. Even in orbiting spacecraft, in which things are "weightless," this is true, because the motions of objects in the spacecraft are observed in relation to the spacecraft to be weightless because everything is falling together, not because gravity has been turned off.
But further discussion of this needs a closer look at movement. For now, what I am saying is that in systems, interactions always involve a loss of energy, and so it is only in bodies, if anywhere, that you will get cycles that are actually equilibrium--and there is even a question there(4).
I might point out that inanimate bodies are bound to look static in equilibrium when compared with living bodies, because the living body is both a physico-chemical body (with, consequently, its equilibrium as such at its minimum energy-level), and, as living, a body that tends to maintain as its special equilibrium an energy-level higher than this ground state. But since the equilibrium as alive is unstable from the point of view of the body as a physico-chemical system, this "maintenance" will take the form of actually gaining and losing energy in a kind of cyclic way(5), and so there will be real changes going on, even though the changes will "hover around" a certain definite high level of energy. But more of that in the next Part.
But having mentioned a body's being unstable, let us now pass on to a definition of this opposite of equilibrium, which will attempt to show what Aristotle was "pointing to" by something's being "in potency."
Instability is the condition in which the unifying energy has a quantity that it cannot exist with in that form. Or, alternatively, it is a condition in which the total amount of the energy of the body is different from the amount that is compatible with that body's being that kind of body.
We said that the total energy of the body reflects the amount of the unifying energy, because the unifying energy has to hold the parts together and make them behave in and for the unit; hence, if the parts have more energy, it is going to need more energy to do the job of unifying the parts. Hence, if the parts have "too much" or "too little" total energy, then this will have to be reflected in some kind of a strain on the energy unifying them; and this strain is instability.
The underlying assumption of this view of the internal cause explaining why a change begins in a body is that every body has a definite energy-level that is compatible with it and that is its equilibrium.
For inanimate bodies, this is the minimum for the particular form of unifying energy in question (or the kind of body in question). For inanimate bodies, of course, this would also mean that two bodies in absolute equilibrium would be totally indistinguishable. "They" could not even be in different places, because to be in a position means to be acted on by other bodies' fields, which of course would involve being unstable to however minimal a degree. A body in absolute equilibrium would have to be in no position at all.(6)
What this amounts to is that no body we are aware of is in absolute equilibrium; but to the extent that physical bodies approach their equilibrium, then bodies of the same kind are indistinguishable from one another. This is another advantage that physics and chemistry have over the life sciences: Since living bodies' equilibria are at a high (and physically unstable) energy-level, there is no one energy-level implied as equilibrium in any given form of life; the same kind of living body can exist in equilibrium at all sorts of energy levels, within a certain range (too little or too much energy destroys it as living, of course).
In any case, when this equilibrium energy-level is disturbed, either by absorption of energy (as is always the case in inanimate bodies, and sometimes in living ones also), or by losing energy so that the internal energy is too low for the equilibrium (which only happens in living bodies), the body cannot exist--and so, of course, it immediately goes out of existence as in this condition(7).
Instability, then, is not a state; it cannot be, because it involves an internal contradiction: the body cannot exist at the energy-level it now exists at. Hence, as soon as instability occurs, it vanishes.
This does not mean, however, that it vanishes all at once, so that instantaneously the unstable body is back in equilibrium; it may be that the energy can't be got rid of in one fell swoop, or that there isn't enough energy around to absorb to regain the high-energy equilibrium all at once. In these cases, the degree of instability vanishes, or lessens in the direction of the equilibrium implied in it.Next
1. Yes, being "active," and not "being in act" in the sense of being "actual" or "complete" or "fully real." Aristotle caught the notion of reality as activity.
2. This "possessing the end inside it" is the meaning of Aristotle's entelecheia, which is also translated "actuality."
3. And is made even vaguer by the abominable translations most people are confronted with.
4. I suppose, of course, that you could say that pure spirits are eternally "in equilibrium," because their activity never changes. But "equilibrium" is contrasted with "changing," and properly applies only to something that can change: that is, a body.
5. But not a real cycle, as in a pendulum, where energy is neither gained nor lost. I am talking here about the body's actually losing energy, and then absorbing a replacement from the environment (as when you breathe or eat).
6. Presumably, if there is a return to life after death for our bodies, then they would then be in absolute equilibrium (though as living, not at their lowest possible energy-level; they would somehow have their energy "closed off" so that they could neither lose nor gain any). In that case, they would not be able to be affected by their surroundings, and consequently would not be in any position. But since a cause is not as such affected by having an effect on something, this does not mean that such bodies could not have effects on the earth. Thus, Jesus could "come through the locked door" after his return to life, because the door could not affect his body. But he could be seen by his students because he could have an effect on them. Evidently, though, his body was quite different from what it was before his death, if John is reporting accurately when he says of the students' facing Jesus at the lake, "And no one dared ask him who he was, because they knew it was the Master." .
7. There is a version of this in inanimate bodies, however, in what are called "endothermic" reactions. Sometimes, the instability reached (by lowering the energy level) is such that the equilibrium it now "points toward" involves a higher energy-level, in which case, it sucks up energy from the environment. It is all very mysterious, but it is the physical basis for the possibility of living bodies. The difference is that the inanimate body is always forced into instability by energy introduced into it, while a living body (as physically unstable) loses energy and then spontaneously produces the proper "endothermic" process.