Free Will, Moral Responsibility, Determinism 19As defined, if determinism is true, a state in the future or instead the present in
conjunction with the laws of nature entails every fact about the past, as well as
the future. Although there is nothing strictly speaking wrong with this way of
defining determinism, for the purposes of the free will debate it is more useful to
foreground determining relations that are temporally directed from past to future.
This is because it is plausible to assume that a person in the present is not free to
act in ways that involves making her past different than it is.^17 Rather, it seems
that if a person has free will, her freedom is a function of how, in the present,
she is able to control her future actions and the consequences of her actions.
Hence, in the pages to follow, we will work instead primarily with this rather
informal definition of determinism:
(D): Facts about the remote past in conjunction with the laws of nature
entail that there is only one unique future.And we will take it to be implicit that the facts picked out are temporally non-
relational facts that can be restricted to specific instants in time, such as just three
minutes after the big bang. This is adequate to capture the simple thought that, if
determinism is true, “given the past and the laws, there is only one possible
future” (van Inwagen, 1983: 65).^18
1.5. Metaphysical, Physical, and Nomic Impossibility
Above, after first introducing the formulation of determinism as the thesis that at
any time only one future is physically possible, we noted two hidden complexi-
ties that needed to be addressed. One had to do with the grounds for only one
future’s being physically possible at any time. We have settled on D as a way of
unpacking that, and D is consistent with how most contemporary philosophers
writing on free will think of the thesis of determinism. The other complexity had
to do with the notions of physical possibility and impossibility. We now turn to a
discussion of that issue.
We have already begun to elucidate the notions of physical possibility and
physical impossibility by explaining how the thesis of determinism can be taken
as a metaphysically necessary conditional truth: for a proposition “P” that
describes the entire state of the universe at some instant in the actual past, and a
proposition “L” that details the entirety of the laws of nature, and a proposition
“Q” that describes the universe at some instant in the actual future, necessarily,
P & L imply Q. Given that P and L are true in the actual world, in the actual
world the non- occurrence of Q would then be physically impossible, which is
just to say that the non- occurrence of Q is inconsistent with the past and the laws
being what they actually are. But note that the metaphysically necessary truth of
the conditional “P & L imply Q” is compatible with the metaphysical possibility
of the falsity of determinism. Even if in all possible worlds P & L imply Q, there
will yet be worlds with a past instant of the entire universe described by P, with
the entirety of the laws, some of which are indeterministic, described by L, and