The Consequence Argument

Posted: Wed, Oct 15, 2025

The free will problem

  1. We have free will.
  2. Determinism is true.
  3. Free will is incompatible with determinism.

Very important: Determinism ≠ fate.

The consequence argument

Peter van Inwagen’s (1983) statement of the argument:

If determinism is true, then our acts are the consequences of the laws of nature and events of the remote past. But it is not up to us what went on before we were born, and neither is it up to us what the laws of nature are. Therefore, the consequences of these things (including our present acts) are not up to us.

He formulates determinism in terms of logical entailment:

  • P0 is a proposition that describes the entire state of the world at time t0.
  • P is a proposition that describes the entire state of the world at a later time t.
  • L is the conjunction of all laws of nature.
  • Determinism: P follows logically from P0 & L.

His toy example: At t, J does not raise his hand.

  • The stylized argument on p. 191.

Local miracle compatibilism

David Lewis: Are we free to break laws of nature?

  • Strong law-breaking ability: We are able to break laws of nature.
  • Weak law-breaking ability: We are able to do things such that, if we did these things, laws of nature would be broken.

Consider: Suppose it was always true that if it was sunny in the morning, Ollie would go to the beach in the afternoon; it was rainy on one particular morning, so they were not at the beach that afternoon.

  • Strong beach-going ability: By going to the beach that afternoon, Ollie would make it the case that it was sunny that morning.
  • Weak beach-going ability: Ollie was able to go to the beach despite the fact that if they went to the beach that afternoon, it would have been sunny that morning.

Strong beach-going ability is not required for Ollie’s ability to go to the beach. Even though Ollie did not exercise their beach-going ability, they retained that ability.

Lewis (1981):

Had I raised my hand, a law would have been broken beforehand. The course of events would have diverged from the actual course of events a little while before I raised my hand, and, at the point of divergence there would have been a law-breaking event—a divergence miracle, as I have called it. But this divergence miracle would not have been caused by my raising my hand. If anything, the causation would have been the other way around. Nor would the divergence miracle have been my act of raising my hand.

Toy example:

  • The actual world: P0 & L → P.
  • Another possible world: P0 & L′ → P′.

Note:

  • P′ is a law-breaking event only relative to the laws of nature that obtain in the actual world.
  • The agent retains, even if they do not actually exercise, the ability to raise their hand such that if they raised their hand, L would be false.
  • But P is also a law-breaking event relative to the laws of nature that possibly obtain in other possible worlds, so local miracles abound!