An Appraisal of Aquinas’ First Way: Quantum Mechanics Contra the Causal Principle? (Part 4)


It is important to understand the background of the argument before undertaking an analysis of objections, so if you have not checked them out, I would suggest reading Part 1Part 2, and Part 3. For each objection, I shall explicate the reasoning behind the objection, followed by an “assessment” section which evaluates the efficacy of the objection in question. Without further ado, let’s examine the second criticism leveled against Aquinas.


Recall that I have characterized the following claim as Aquinas’ causal principle (found in P4): whatever is changed is changed by another. Some claim, however, that physics has refuted this principle. Physics, one may argue, establishes that certain particles (called virtual particles) can snap or leap into and out of existence randomly and without a cause or actualizing changer. Some particles decay without rhyme or reason and without something prior actualizing such a decay. Some particles follow one slit rather than another (and thereby change) randomly and hence without an actualizing cause. But if these criticisms are correct, P4 is false.


First, it is contestable whether such results do, in fact, warrant the claim that such events are utterly uncaused, lacking in any explanation or actualization. Indeed, such indeterminacy only arises under a fraction of the interpretations of quantum mechanics (examples of interpretations include Copenhagen, Many Worlds, Bohmian, and so on). There is by no means universal support among physicists as to which interpretation is correct. Second, the present evidence underdetermines which quantum theoretical interpretation is correct. The empirical evidence in and of itself is not, at present, sufficient to determine which of the competing theories is true. Thus, quantum mechanics has not established such “leaps” to be features of reality.

Third, in discussing change and causation, we must distinguish between two types of effects: demanded, necessitated effects and dependent effects. While all effects are dependent upon prior actual states, not all effects are demanded, determined, or necessitated by prior states. Applying this to quantum indeterminacy, virtual particles may not be demanded or necessitated by prior states, but that does not entail that such particles do not depend on prior states. When a particle “spontaneously” appears or decays, perhaps nothing demanded that this precise event would obtain. It would be a mistake, though, to infer that such events emerged from absolutely nothing. Indeed, we have ample reason to think that such quantum mechanical events emerge from and are dependent upon prior energy states, and that such systems evolve according to quantum mechanical laws. The seemingly spontaneous occurrence, then, is dependent upon prior actualities in that they depend upon prior energy states and laws of nature. As philosopher Joshua Rasmussen emphasizes, Aquinas’ causal principle “says that mere potentials cannot become actual without something to actualize them. This principle leaves open how an actualizer actualizes its effect: maybe it demands the effect, or maybe it provides the conditions for the effect to come about spontaneously.”11

Fourth, one may object that we evidently are not aware of and do not see or detect a prior cause or actualizer. But “I do not see the existence of an actualizer” is crucially different from and does not entail “I see the non-existence of an actualizer”, just as “I am not aware that my thoughts are correlated with neurophysiological states” is different from and does not entail that “I am aware that my thoughts are not correlated with neurophysiological states”.

Fifth, I would argue that science, in principle, could never establish that the particles or quantum processes arise from pure, absolute, utter non-being. Consider that science, by its nature, is inherently restricted to that which is empirical (i.e. able to be detected by our senses directly or indirectly via instrumentation). But “nothingness”, by definition, is not empirical (not sensible or detectable). Hence, science is limited in such a way that disallows for it to establish that the particles spring into existence inexplicably from nothingness.

Sixth, arguably there are elements within Thomistic metaphysics that not only anticipate spontaneous events, but also adequately subsume them under the causal principle. On this point, Feser writes:

“Some thinkers, and Aquinas in particular, take the view that a substance can manifest certain dispositions in a ‘spontaneous’ way in the sense that these manifestations simply follow from its nature or substantial form. A thing’s natural tendencies vis-à-vis local motion would be an example. These motions simply follow from the thing’s substantial form and do not require a continuously conjoined external mover. Now, that is not to say that the motion in question does not have an efficient cause. But the efficient cause is just whatever generated the substance and thus gave it the substantial form that accounts (qua formal cause) for its natural local motion.”12

In place of Feser’s example of local motion (i.e. change with respect to spatial location), though, simply place “quantum mechanical phenomena”. In summary, then, a Thomistic metaphysical framework can provide tools to reconcile spontaneous events with the causal principle, since such spontaneous acts are wholly grounded in the nature or essence of the thing or process in question, and the nature or essence in turn is accounted for in terms of whatever causally accounted for the substance’s or process’s beginning of existence.

Seventh, physics (especially the highly theoretical and mathematical branches of physics) provides us with a description of the mathematical and abstract structure of physical reality. It abstracts away from reality any aspect which cannot be neatly captured by its purely quantitative methodology. This is relevant to the quantum mechanical objection since “from the fact that something doesn’t show up in the description physics gives us, it doesn’t follow that it isn’t there in the physical world. This is like concluding from the fact that color doesn’t show up in a black and white drawing of a banana that bananas must not really be yellow. In both cases the absence is an artifact of the method employed, and has nothing whatsoever to do with the reality the method is being used to represent.”13 But because quantum physics gives insight almost exclusively about abstract, mathematical, and structural relations in which quantum particles stand, it is (by the restrictions of its very own abstractive methods) mostly silent on the intrinsic natures of the micro-level phenomena in question. In that case, though, claims about the intrinsic characters of quantum processes and phenomena as objectively random and inexplicable are beyond the realm of scientific inquiry.

Now, a full-blown defense of epistemic structural realism (the view briefly defended above) in theoretical and mathematical physics requires much more by way of exposition and argument. I have only given a brief outline. My point in bringing it up, however, is to provide yet another plausible avenue by which Aquinas’ argument may be defended against the quantum mechanical objection.

We have seen seven reasons to reject the objection from quantum mechanics to premise four (the causal principle) of Aquinas’ argument. Thus far, Aquinas’ argument is on good footing. We shall turn in the next post to a bootstrapping objection to Aquinas’ argument.

Author: Joe


11. Rasmussen, “How Reason Can Lead to God,” 40-41.

12. Feser, “Causality and Radioactive Decay.”

13. Feser, “Causality and Radioactive Decay.”


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  6. “But the efficient cause is just whatever generated the substance and thus gave it the substantial form that accounts (qua formal cause) for its natural local motion.”

    What? That doesn’t even make sense. What does Feser mean by “generated”? Does he mean “created” it? Because if that’s the case, then one can simply challenge the unjustified presupposition that the substance in question (viz., the quantum vacuum — which is the material cause and necessary/sufficient condition for the event) was created/generated.

    Sure, the event only occurs if the necessary and sufficient conditions are in place, but that doesn’t mean the vacuum is the efficient cause of the event. All it means is that the vacuum allows the event to take place without an efficient cause. For example, take a tree that spontaneously becomes a chair. The event can only occur if the necessary and sufficient conditions are in place (i.e., the material cause, space to be in, time, all the forces working and holding the atoms together and so on). However, in this case, there simply is not an efficient cause turning the tree into a chair! So, from the fact that the tree was generated/created (and hence had an efficient cause), it simply does not follow the chair had an efficient cause.

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