18 Free Will, Moral Responsibility, Determinism
(e.g., van Inwagen, 1983: 65). This is in part because since Hume a number of
philosophers have regarded the concept of causation as controversial, and some
have doubted that there really are causal relations in the world. As a result, some
philosophers have opted to work with the thesis of metaphysical entailment
determinism, which is formulated in a way that makes no reference to causation
at all. So, consider this formulation, which is a variation on one offered by van
Inwagen (1983):
metaphysical entailment determinism: If p and q are propositions that express
the entire state of the world at some instants, then the conjunction of p with a
proposition expressing the entirety of the laws of nature entails q.^13What is doing the work of ensuring that only one future is physically possible is
the logical relation of entailment, along with propositions about both the laws of
nature and the state of the world at a time.
On metaphysical determinism, it’s metaphysically impossible, given the facts
about the world at a time and its laws that the world at any other times be differ-
ent (that is, different from what is expressed in the entailment). Another way of
expressing this is that it is a metaphysical truth about the nature of that world
that its physical facts are fixed in this strong way—for these facts to be other-
wise, while the history of the world and the laws of nature remaining as they
actually are, would involve a violation of metaphysical necessity.
Several ingredients in the preceding definition can be clarified. A first is the
notion of the entire state of the world at an instant. The sense of “the world” here
is all of physically extended reality at an instant. Second, the facts that the defi-
nition should be understood to specify by “the state” are all and only the tempor-
ally non- relational facts. That is, they are facts that, at that instant, are not
logically dependent on facts about other times—and they are, or entail, all of
those facts.^14 Another ingredient is the notion of a law of nature. Paradigmatic
examples are the inverse square laws that govern gravitation and electromagnet-
ism. We will not attempt to offer anything like a definition of what a law of
nature is. As it turns out, it is hard to do this. But we can say that they are non-
accidental, factual regularities that seemingly involve necessities, limits, con-
straints, or requirements on how the natural world unfolds.^15 However we are to
understand laws of nature, they are such that, if an event contravenes what seems
to be a law of nature, then what seemed to be a law of nature was no law of
nature after all (e.g., van Inwagen, 1983: 61–2). If, for instance, it is claimed that
it is a law of nature that nothing can travel faster than the speed of light, and if
an alien space ship does in fact travel faster than the speed of light, then the
claim was mistaken and it is no law of nature that nothing can travel faster than
the speed of light. We would have discovered that something we thought to be a
law of nature was not one.^16
The preceding definition of determinism, while adequate, is not intuitive as a
means to addressing various issues in the free will debate. This is because it does
not temporally privilege the direction of past to future; it is neutral on this point.