Aquinas, Duns Scotus, and their followers on self-motion and the generation of new substantial forms

The classic argument against self-motion

From Saint Thomas’ First Way:

Now whatever is in motion is put in motion by another, for nothing can be in motion except it is in potentiality to that towards which it is in motion; whereas a thing moves inasmuch as it is in act. For motion is nothing else than the reduction of something from potentiality to actuality. But nothing can be reduced from potentiality to actuality, except by something in a state of actuality. Thus that which is actually hot, as fire, makes wood, which is potentially hot, to be actually hot, and thereby moves and changes it. Now it is not possible that the same thing should be at once in actuality and potentiality in the same respect, but only in different respects. For what is actually hot cannot simultaneously be potentially hot; but it is simultaneously potentially cold. It is therefore impossible that in the same respect and in the same way a thing should be both mover and moved, i.e. that it should move itself. Therefore, whatever is in motion must be put in motion by another.

Criticisms of the argument

A skeptic would respond as follows.  This principle of proportionate causality (PC–It’s called several things in the literature.  I took this name from Edward Feser.) doesn’t even work for Saint Thomas’ chosen example, in that cold objects can become hot through friction or exothermic chemical reactions without any prior thing being hot.  Whatever agent causes the heating must be in act in the sense that it must exist and have some power to influence the heated object, but it needn’t itself possess the actuality of being hot.  For that matter, an object can cool itself without being influenced by a cooler body, e.g. through blackbody radiation.  Thus, if Aquinas means that the cause must possess the form it actualizes in the effect, this conflicts with experience.  Nor is it obvious a priori why forms can only impress themselves and not causally connect to other forms.  Alternatively, one could propose a more modest PC principle, that the effected act pre-exists in the cause only in the sense that the cause possesses a power to effect the relevant change, but then the principle is tautological, and the argument against self-motion collapses.  It gives no reason why a being may not have a passive potency to receive x, an active potency to cause x (due to the possession of some other form), and may then act on itself without any need for the two potencies to reside in different parts.

The evolution and chemistry debates

Although the strong form of PC presents grave difficulties, it exerts a great deal of influence on the Catholic intellectual world, as seen particularly in discussions of the theory of evolution.  Recently, Fr. Michael Chaberek has written a book, Aquinas and Evolution, arguing that the evolution of new species is incompatible with Thomism because it violates this principle; at some point (if species are equivalence classes, as a Thomist will no doubt insist they are) parents must produce an offspring of a different species.  Fr. Nicanor Austriaco replies in Public Discourse, quite correctly, that the same argument could be made to prove that hydrogen and oxygen cannot combine to form water.  (That is, even a strong-PC advocate will allow that H and O can be material causes of existing water, but cannot allow that they can be efficient causes of water to be produced.  Note that Thomist holism actually makes the problem worse.  If molecules/compounds were nothing but their component atoms/elements, there would be no problem, but the current Thomist position is to grant full reality only to wholes and only virtual reality to parts.)  The conclusion is absurd, but how to avoid it within a Thomist framework?  Austriaco suggests (with precedent in Aquinas’ Aristotelian cosmology) that more perfect substantial beings may be involved, namely God or His angels.  Just as such beings can enable chemistry, so could they enable the evolution of new species, and before that the origin of life itself.  The appearances are saved, and we needn’t deny that chemical reactions happen, but look at the price!  We must invoke miraculous divine (or at least angelic) intervention to explain perfectly ordinary (actually, ubiquitous!) natural phenomena.  We have been led to a position not far from occasionalism.  Should this not cause us to reflect on whether the metaphysical principle that so consistently engenders outlandish conclusions is really certain?

Physically possible but metaphysically impossible?

Most people assume that the set of metaphysically possible processes is larger than and includes the set of physically possible (i.e. consistent with scientific laws) processes.  In some versions of Thomism, this appears not to be the case, in that the laws of physics and biology continually predict changes that are metaphysically impossible, and God (or His angels) must constantly intervene just to make the scientifically expected changes occur.  I have pointed this out before in the context of the origin of life and human ensoulment.  As Father Austriaco’s example makes clear, secondary causality really doesn’t extend very far at all with strong PC.

Again, it is possible that this is true, just as it is possible that full occasionalism is true, but it clashes violently with my intuition.  Fortunately, disciples of Aquinas aren’t stuck with it.  Thomists such as Dr. Feser point out that effects can exist virtually or eminently in their causes (basically allowing PC to become the tautological “The cause must have the power to produce the effect”).  But the extreme view is influential.

Duns Scotus on self-motion

The Catholic intellectual tradition as a whole has been open to wider possibilities of possible causality.

I’ve just been reading an interesting conference proceedings entitled Self-motion:  from Aristotle to Newton.  Many of the papers address the apparent conflict, which had been perplexing me, between Aristotle’s denial of self-motion in the Physics and his usual treatment of animals as self-movers.  The most fascinating contribution, though, is Peter King’s “Duns Scotus on the Reality of Self-Change”.  It seems that the Subtle Doctor put forward detailed arguments for the possibility of self-change within an Aristotelian framework.  Scotus painstakingly distinguishes different senses in which a potency or act can be in a subject, shows how common arguments against self-change confuse these senses, and that when all terms are used consistency much weaker conditions are obtained, which although not trivial do not rule out self-motion.  Scotus argues for what was then considered the least defensible case of self-motion, namely locomotion of inanimate objects, such as the elements naturally rising or falling.  Having clarified principles, Scotus believes causality can be univocal (an active form imprinting itself) or equivocal (an active potency to actualize a different form in a subject–possibly itself–with the appropriate passive potency).  A world with self-motion is, he thinks, more excellent and more unified (via causal connection between forms) than one without such powers.  Does this sink Aristotle’s argument for a prime unmoved mover from motion?  Scotus thinks not.  He thinks the argument can be formulated in terms of causes of the potency for change (including self-change) rather than the cause of change itself.  (Thus, the argument from motion would, he would say, be valid even in a stationary universe.)

Scotus’s work was just the beginning of a fruitful reassessment of Aristotelian physics in the 14th century, led by William of Ockham and Jean Buridan, which rejected the need to invoke the air or celestial bodies or angels to explain locomotion, replacing this with something like the modern concept of inertia, while Nicholas Oresme pioneered the mathematical study of motion.  It is unfortunate that Catholicism today has largely truncated its engagement with Scholasticism at the 13th century.

Conclusion

There are plenty of ways to accommodate Aristotelian principles to science and daily experience.  That’s not the problem.  The problem is that we need the problematic ones to do the necessary work in the argument from motion.  One could try to save the argument by switching at a key point from motion (in the Aristotelian sense:  activation of a form in a pre-existent substratum) to some more metaphysically basic category.  Duns Scotus does this by switching from motion to potencies for motion.  Dr. Feser does it in his new book on arguments for God’s existence by switching from motion to existence, a more basic kind of act.  In both cases, one finds oneself on stronger ground.  I would prefer to just admit that the classic argument from motion is invalid and drop it.