Contemporary Incompatibilism: Libertarianism 25110.10. Is Agent- Causation Reconcilable with the
Physical Laws?
The coherence of agent- causal libertarianism is perhaps in doubt, but it has not
been decisively undermined. Pereboom (1995, 2001, 2014) argues, however, that
we have empirical reasons to conclude that it’s improbable that we are agent
causes of the sort set out by this view. These reasons concern whether agent-
causal libertarianism can be reconciled with our best physical theories. On agent-
causal libertarianism, when an agent decides freely, she causes the decision
without being causally determined to do so. But if the decision results in changes
in her brain or in the rest of her body, she at some point would affect the phys-
ical world distinct from herself as agent- cause. However, on our best physical
theories the physical world is law- governed. Suppose first that the physical laws
are causally deterministic (Kant, 1788/1996: Ak V: 97–8). This is what Kant
maintains, but on his agent- causal picture, when an agent makes a free decision,
she causes the decision without being causally determined to do so. But on the
causal route to action that begins with this decision, alterations in the physical
world, for example in her brain or some other part of her body, are produced.
But it would seem that we would at this point encounter divergences from the
deterministic laws. For the alterations in the physical world that result from the
undetermined decisions would themselves not be causally determined, and they
would thus not be governed by deterministic laws. One might object that it is
possible that the physical alterations that result from free decisions just happen
to dovetail with what could in principle be predicted on the basis of the deter-
ministic laws, so nothing actually occurs that diverges from these laws. But this
proposal would, at least prima facie, involve coincidences too wild to be cred-
ible. For this reason, it seems that agent- causal libertarianism is not reconcilable
with the physical world’s being governed by deterministic laws.
Recent expositors of agent- causal accounts, Clarke (1993, 2003) and
O’Connor (2000, 2009) in particular, propose that quantum indeterminacy can
advance the reconciliation project. On one interpretation of quantum mechanics,
the physical world at the micro- level is not deterministic, but is governed by
laws that are fundamentally merely statistical or probabilistic. Suppose, as is
controversial, that significant quantum indeterminacy percolates up to neural
indeterminacy at the level of decision. This constitutes a prima facie case for the
claim that agent- causal libertarianism is reconcilable with the laws of physics.
Still, wild coincidences would seem to arise on this proposal. Consider the class
of possible human actions each of which has a physical component whose ante-
cedent probability of occurring is approximately 0.32. It would not violate the
statistical laws in the sense of being logically incompatible with them if, for a
large number of instances, the physical components in this class were not in fact
realized close to 32 percent of the time. Instead, the import of the statistical law
is that for a large number of instances we can expect physical components in this
class to be realized close to 32 percent of the time. But if agent- caused free
action were compatible with what according to the statistical law is highly likely,