Skip to main content

Aquinas' First Way: Unmoved Mover

Formulation​

  1. Some things are in motion.
  2. Everything that is in motion is moved by something else.
  3. An infinite regress of movers is impossible.
  4. Therefore, there must be a first mover, an unmoved mover, that is not moved by anything else (God). (2, 3)

Metaphysical Underpinnings​

Act-Potency Distinction​

Aquinas' argument relies on the distinction between act and potency.

  • Act: What things are in actuality.
  • Potency: What things can potentially be.

Both are conceived as "modes" of being, so they are all real.

Parmenides was an ancient Greek philosopher who argued that change is impossible:

  1. Change requires a being to arise from nothingness.
  2. Nothingness cannot produce anything.
  3. Therefore, change is impossible.

Aquinas' act-potency distinction allows him to avoid this problem. However, it also leads to some other problems.

First, the act of staying the same is also a kind of change, and can be seen as a kind of potentiality. This means that everything has at least one potential, that of staying the same. This "everything" includes the unmoved mover, which means that the unmoved mover is not actually unmoved.

Second, many philosophers argue that it leads to an actual infinity of potentials. Consider a fluid in a container at . It has the potential to be at , , , and so on - an infinite number of potentials. Recall that Aquinas' argument relies on the real nature of potentials to avoid Parmenides' argument. Therefore, there are an infinite number of actual things; an actual infinite.

Compatibility with Eternalism (B-Theory of Time)​

The A-theory of time is the view that time is a series of moments. Up until recently, this was the dominant view of time, and is probably what most people intuitively think of when they think of time.

Eternalism is the view that all times are equally real. Instead of thinking of time as a series of moments, we can think of time as a four-dimensional block. Modern physics, especially general and special relativity, seems to support this view.

The problem arises when we consider Aquinas' argument in the context of eternalism. If all times are equally real, then change would not be some "actualization of potential". This would unermine the entire underlying metaphysical framework of Aquinas' argument.

Pluralism about Beings​

Aquinas' argument seems to rely on a kind of pluralism, suggesting that there are different kinds of beings. This is a controversial view, and many philosophers reject it due to the following reasons:

  1. Pluralism lacks coherence and clarity. It is unclear what the different modes of being are, their relations, classification, interactions, etc.
  2. Pluralism leads to ontological inflation. It seems to multiply entities beyond necessity, making it difficult to distinguish fundamental entities from derivative ones.
  3. Pluralism is seen as non parsimonious. It opposes the view that everything can be explained in terms of a single fundamental entity or principle.

Existential Inertia​

Inertia refers to when an object remains in its current state unless acted upon by an external force. In Physics, this is a fundamental principle (Newton's First Law), and it is also a fundamental principle in metaphysics. Essentially, existential inertia states:

Things remain in existence unless acted upon by an external force.

Hence, things do not need some sustenance or maintenance to continue existing.

This means that the first mover does not need to continuously move things to keep them in motion.

Validity of the Conclusion​

Pay close attention to the conclusion of the argument: that there must be a first mover. This does not necessarily follow from the premises.

First, in some causal chain, there might be a first cause, and the other beings in the chain have this "causal power" derived from the first cause. For example, consider a row of dominoes. The first domino contains the causal power in respect to movement, and the other dominoes have this power derived from the first domino.

This does not mean, however, that this first cause is necessarily uncaused. This first cause might be unactualized in one respect, but perfectly able to actualize in another respect. For example, the first domino could be unactualized in respect to movement, but perfectly able to actualize in respect to heat.

Second, this is the more obvious objection: the argument does not necessarily lead to the traditional conception of God. Naturalists can accept the existence of a first cause, but they would not accept that this first cause is God. For example, they could accept a collection of physical symbols, like quarks or strings, or some quantum field or universal wavefunction, or an initial singularity. THey could also simply the universe itself as the foundation of all things.