What is Classical Theism (Part 2)

In part 1, we laid out some of the groundwork distinguishing “signpost arguments” for something supernatural from “metaphysical demonstrations” for the God of classical theism.

Now, in part 2, we examine one of these metaphysical demonstrations: an Aristotelian proof of God’s existence. Dr. Edward Feser defends this demonstration in his recent book. Let’s jump right in.

The proof is Aristotelian in the sense that it employs key notions from Aristotle. Particularly, his theory of potentiality and actuality, which are necessary preconditions of a world with any real change.

The Outline

I summarize this argument as follows:

  1. Change occurs.
  2. Change entails a distinction of actuality and potentiality.
  3. Change requires a changer, and more generally, actualization requires an actualizer.
  4. The existence of things here and now requires a hierarchically ordered causal chain of actualized potentials.
  5. Hierarchically ordered causal chains of actuality and potentiality cannot go on indefinitely, but must terminate in a first member, who is pure actuality.
  6. There exists a first mover (the first member of the chain) that is pure actuality.
  7. The first mover, existing as pure actuality, possesses the divine attributes.
  8. The first mover is God.
  9. Therefore, God exists.

In this blog series, we unpack these premises in detail to defend this metaphysical demonstration. If the terms are clear, the premises are true, and the argument is valid, we reach the conclusion inescapably.

Premises 1 and 2

Change occurs. This hardly needs defense. We observe things moving all around us. Brownies cool down upon removal from the oven. People learn to waltz. A friend loses 30 pounds. Radioactive material decays. That things undergo change seems to be an obvious facts of reality.

However, did you know there were ancient Greek philosophers who denied this reality? Zeno and Parmenides are two of the most famous. Putting aside the archaeological and historical difficulties of determining what they actually said, we consider the following position typically attributed to them.

These Greek skeptics held that nothing changes. They argued: in order for genuine change from A to B to occur, nonbeing would need to produce being. In other words, when A is only A, B does not exist. So, the being of B would have to come from the nonbeing of B. But nothing can come from nonbeing, since nonbeing is simply the negation of being and cannot do anything. So, they argue, nothing can actually change.

Zeno goes on to present famous paradoxes that supposedly disprove them the occurrence of local motion. However clever the arguments, the conclusion is bizarre and repugnant to common sense.

Aristotle’s Answer

Aristotle answered these philosophers by distinguishing actuality and potentiality. He agreed with Zeno and Parmenides that being could not come from nonbeing. However, he denied that change required this.

Aristotle recognized that some things exist in things actually while other things exist potentially. Consider the JC Penny brand shoe horn currently on the desk in my office. It actually exists as a bent, slightly malleable, piece of plastic. Those characteristics are exemplified in the shoe horn here and now.

Nonetheless, the shoe horn is potentially other ways. It is potentially a melted pile of goo (if put under severe temperatures). The shoe horn is potentially snapped in half. The curvature of the object is potentially warped more than in currently is at the moment. It does not have all potentials. The shoe horn is not potentially thoughtful. It is not potentially able to speak or turn on my television.

So, the shoe horn exemplifies some characteristics in an actual way and it has the capacity to have other characteristics (its potentialities). These potentials are real.

This division of being, between actuality and potentiality, shows that when A becomes B, A must have the potential to become B. This potential to become B is not nonbeing, but rather being of a different sort. Either one can accept this being of a different sort or one is stuck with the absurd conclusion that being comes from nonbeing or that nothing really changes.

So, anyone who accepts the reality of change requires this distinction between actuality and potentiality a requirement

A Cartesian Objection 

Despite this, some might still side with Zeno that all change is an illusion. Descartes proposed a famous thought experiment where an evil demon possibly deceives us all. Perhaps, says Descartes, reality does not correspond to our sense experience, but rather we merely have the sense experiences the evil demon wants us to have! This compares to a “Matrix” scenario, where we fail to experience reality directly as computers and wires feed us experiences.

Now, even on this radically skeptical scenario, the reality of change persists. Zeno, Parmenides, Descartes, and others must propose their arguments or thought experiments. Their audience must assess their merit. And, if convinced, they will grasp the conclusions of their arguments. This mental assent and reasoning requires change.

Zeno’s disciples once did not know his arguments and then came to understand them. This demonstrates a change from lacking a certain understanding to understanding. So, the reality of change is an unavoidable fact of reality.


As we have seen, change occurs and change entails the distinction between actuality and potentiality. So, we have established premises (1) and (2) in our Aristotelian metaphysical demonstration.

In part 3, we turn to a defense of premises 3, 4, 5 and 6. If you want all the details right away, check out Dr. Edward Feser’s great new book: Five Proofs of the Existence of God.

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