Friday, July 13, 2012

A Restricted Causal Premise in the Argument from Motion

The argument from motion usually takes on something like the following form:

1. Evident to the senses is motion. (Premise)

2. Everything in motion has its motion sustained by another. (Premise)

3. Either an Unmoved Mover exists, or else there is an infinite regress of sustaining movers. (Implied by 1 and 2)

4. There cannot be an infinite regress of sustaining movers. (Premise)

5. Therefore, an Unmoved Mover exists. (From 3 and 4)

I believe this argument is sound.  Suppose, however, that one is convinced that Newtonian, Einsteinian or quantum physics somehow undermines premise (2).  Notice I'm not agreeing, and I think such an objection is based on a misinterpretation of both contemporary physics and Aristotelian metaphysics.  Nevertheless, even if the objection were a good one, the argument can easily accommodate this point.

(2) can become (2*): There is a regress of things in motion that requires its motion to be moved by another.

If this is correct, then the existence of an Unmoved Mover may still be deduced.  For example, an acorn's potentiality to become an oak tree cannot actualize itself.  Rather, its motion is causally dependent on the sustaining power of the acorn's environment, e.g. soil, water and sunlight.  Hence, if the regress of sustaining movers cannot be infinite in this instance, then the conclusion that an Unmoved Mover exists remains a sound one.


  1. I've been reading Edward Feser's Aquinas lately, and noted the following passage:

    "Change just is the realization of some potentiality; or as Aquinas puts it, 'motion is the actuality of a being in potency' (In Meta IX.1.1770), where 'motion' is to be understood here in the broad Aristotelian sense as including change in general and not just movement from one place to another."

    Is this the technical sense of "motion" you're utilizing in your argument, or do you think the argument works even if "motion" is limited to its plain sense of "movement from one place to another"?

  2. I prefer to think of it as change in general. Local motion is indeed a type of change, as well, and I imagine it could be used in the argument. However, I also think it's best to do an end run around all of that and focus simply on the actualization of potentialities. This is what the analogy of the acorn and oak tree does.

  3. Interesting Doug. To play devil's advocate, do you think (2*) still runs afoul of the quantum mechanics objection (i.e. the decay of this particle is uncaused)? Would you respond (as I would) that this decay is still subject to a formal cause, which in turn needs to be actualised (i.e. the form/essence given an instance of existence)?

  4. Andy, I would start with that reply. Since the first way is concerned mainly with formal causality, it's often misinterpreted with the second way which deals with efficient causality. However one looks at it, though, there is no decay (whether spontaneous or determinant) apart from some necessary conditions.

  5. 1. How do you justify premise (4)?

    2. Your argument concludes that there is one unmoved mover. Why can't there be more than one?

    3. Your premise (3) also leaves out the option of a *prior* unmoved mover who longer exists.

    4. What do you mean by motion? Presumably, motion occurs when object O at location L subsequently appears at location L2, where L and L2 are different points in space. This is questionable at the quantum level where objects don't "move" from one spatial point to another (rather, different objects pop in and out of existence). A lot depends on your definition of motion, which you have yet to provide.

  6. Hi Spencer,

    I've written extensively on each of the argument's premises elsewhere. However, here's a quick summary of how a defender of the argument could respond.

    1. Premise (4) is justified on the grounds that it is impossible to form an actual infinite by successive addition, at least whenever one begins counting. Suppose that the past is infinite. It is still composed of finite intervals. At each finite interval, the regress of sustaining causes of motion begins anew. Therefore, the regress of the sustaining causes of motion must be finite.

    2. The argument laid out above doesn't seek to establish that there is only one Unmoved Mover. Nevertheless, the oneness of the Unmoved Mover can be established through other arguments:

    3. An Unmoved Mover cannot cease to exist, since ceasing to exist is a change. The Unmoved Mover is immutable.

    4. I hint at a definition of "motion" in the final paragraph. Motion is any type of change of potentiality to actuality. As I said, even if QM is inconsistent with the original argument from motion, the theist can easily accommodate this point.

  7. This is very impressive. I need to spend some time reading past posts.