Existential inertia in terms of inertial actuality

This is part two of my follow-up to my original post on potentiality and inertia, where I respond to comments made by defenders of existential inertia. In the previous post we delved deeper into the nature of potentials, and saw that not everything we call a potential is equally deserving of the name. This helped us clarify the indifference of potentials, and how they relate to their actualizations. In my estimation, the indifference of potentials is the core reason for thinking that potentials depend on some other actuality for their continued actualization. In the course of this post, we will have an opportunity to further unpack these two ideas and the connection between them.

The objection of interest for this post is raised both by Joe Schmid and Graham Oppy in different contexts. Oppy, in responding to a paper by Feser, says the following:

Yesterday, throughout the entire day, there was a red chair in my room. Pick some time t around noon yesterday. At t, the chair existed, and the chair was red. Moreover, at t, the chair had the potential to exist, and to be red, at t + ε, where ε is some relatively short time interval (say, a millionth of second). Do we need to postulate the existence of some distinct thing that exists through (t, t + ε) that actualizes at t + ε the potential that the chair had at t to both exist and be red at t + ε? I do not think so. Given that, at t, the chair has the potential to exist and to be red at t + ε, all that is required for the realization of this potential is that nothing intervenes to bring it about, either that the chair does not exist, or that the chair is not red, at t + ε. Potentials to remain unchanged do not require distinct actualizers; all they require is the absence of any preventers of the actualization of those potentials. In particular, things that have the potential to go on existing go on existing unless there are preventers — internal or external — that cause those things to cease to exist.1

In private correspondence, Schmid has raised a similar objection: even if we grant the continued indifference of potentials, all we need is some kind of explanation, not necessarily an explanation in terms of a concurrent sustaining efficient cause. The persistence in actuality could be explained by a whole host of explanatory factors that don’t invoke sustaining causes — for example, the prior state and existence of the object combined with no sufficiently destructive causal factors, or in terms of an existential inertia tendency, or something else.

It may come as a surprise, but for the most part I am in agreement with Oppy and Schmid: it is often the case that something with an actualized potential P does not require some external sustaining cause to sustain the actualization of P. As I mentioned in my original post, Newtonian inertia is a great example of this: physical objects remain maintain their rectilinear motion until some other thing causes them to stop. And the example of the chair’s “inertial color” given by Oppy is another good example: the chair maintains its color until something causes it to be another color. The trouble is that these examples don’t undermine a more nuanced rejection of existential inertia.

In my original post, we saw that the indifference of potentials is consistent with inertial behavior because of what we termed “inertial actualities”. There we arrived at these in a fairly roundabout way, but we can get to them more directly as follows. Say we have some S with potential P and its actualization A at time t, and we want an account of how A persists until some later time t+ε. Given that potentials are indifferent to their actualizations, it can’t be that P keeps A around. Of course, the continued existence of P is necessary for the continued existence of A, but its indifference to A makes it insufficient for the task. There must be something else in the picture, that isn’t indifferent to the continued actualization of P. At this point, a proponent of existential inertia might note that this could be an intrinsic aspect of S to maintain A in the absence of contrary causes. And it certainly could be, but we can know more about it. Since it’s not indifferent to A, it cannot be another potential. And since being is divided into potentiality and actuality, it must therefore be an actuality. Moreover, this actuality must be closely connected to P in a way that other actualities in S are not. This is what I call an “inertial actuality” since it’s an actuality that explains the inertial behavior of the actualization of P.

Going further, I have suggested that we understand an inertial actuality as an incomplete determination to some behavior, in such a way that it allows for variation in the details of how that behavior plays out.2 This incomplete determination gives us potentials for the actuality to express itself in concrete ways. The example of interest in my original post was Newtonian inertia: by virtue of something existing as a physical thing it is determined to continue its rectilinear motion (behavior) but does not fix the vector of that motion (incomplete). Let’s say we’re considering the potential some S has to be moving along some vector V. This potential arises from the incomplete determination of S to continued rectilinear motion, but is (as all real potentials are) indifferent as to whether S is actually moving along the relevant vector. However, when the potential is actualized in S, by virtue of the underlying inertial actuality S will continue along V until stopped by something else. This isn’t because P has somehow stopped being indifferent to its actualization, but because P exists in virtue of an underlying inertial actuality that was never indifferent to S’s motion. Similarly, the material constitution of a typical chair entails that it will have some color, but is consistent with this color being one among a wide range of options. Again, this incomplete determination gives rise to a variety of potentials, each of which is indifferent to whether it is actualized. But when one is actualized, the material constitution of the chair (not the potential) ensures that it will remain actualized in the absence of contrary causes.

Thus, the inertial behavior we observe in the world points us to the lower-level inertial actuality that gives some potentials existence and maintains their actualizations in the absence of contrary causes. The relationship between the two isn’t ad hoc, either, for it is the incomplete determination to the relevant behavior that gives rise to the potentials in the first place. Furthermore, such incomplete determinations have long been recognized when thinking about change, apart from questions of existential inertia.3

All of this helps us see that Oppy’s “potential to remain unchanged” is just another example of a pseudo-potential, this time made up of the potential and the inertial actuality from whence it arises. And it also helps us see the truth of the point made by both Schmid and Oppy, that the indifference of potentials doesn’t necessitate some external sustaining cause outside of the thing with the potential, for the inertial actuality is neither external nor an efficient cause.

Where does this leave us on the question of existential inertia? I think there are two things we can say here.

First, we are still left in need of external causes for actualized potentials that can’t be sustained by some lower-level inertial actuality. Aristotelians have traditionally recognized the distinction between prime matter and substantial form, and Thomists have recognized the real distinction between essence and existence.4 Now, both prime matter and essence are potentials that have no lower-level actualities, and therefore there can be no inertial actuality to maintain their actualizations. In these cases, then, we would need some external cause to sustain the actualizations of these potentials.

Second, we can shift the question of existential inertia from substances to their potentials and actualities, and thereby render moot the question of external efficient causes. The question of existential inertia typically arises in the context certain arguments for God’s existence, such as Aquinas’s argument in On Being and Essence5 and his second way.6 These formulations frame the argument in terms of efficient causes of existence, but strictly speaking all we need is the actualization of potentials by other actualities. That is, we can start with some actuality and build an essentially ordered series of actualizers leading back to a pure actuality. The question of whether this requires a separate substance from the one we started with can be settled as a corollary of what it means to be pure actuality. Despite sounding similar to Aquinas’s first way — which is also construed in terms of actuality and potentiality — this is in fact a different argument. The first way proceeds from the reduction of potentiality to actuality, whereas this argument proceeds from the continued actualization of potentials.

The upshot of all of this, I think, is a more nuanced understanding of existential inertia and its rejection. When we discuss the continued existence of some aspect of reality, we need to get clear on whether it can be explained by some inertial actuality within a substance or not. And if we wish to establish a separate sustaining cause of something, then we need to be clear on which potentials we’re considering within that thing, for not all require such an explanation.


  1. Graham Oppy, “On stage one of Feser’s ‘Aristotelian proof’”.↩︎
  2. There we spoke about this in terms of form and matter, but for this post we will try to restrict ourselves simply to language of actuality and potential.↩︎
  3. For example, they arise in the distinction between substantial and accidental forms in the course of making sense of the difference between substantial and accidental change.↩︎
  4. For my previous discussions on these, see my posts on God, matter, and necessary existence and the real distinction.↩︎
  5. See the bottom of page 240 here.↩︎
  6. See the corpus of ST I Q2 A3.↩︎

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