112 Alternative Possibilities and Frankfurt Cases
just because it is natural to assume that the actual causal history of an event is
essentially the same in each, given that the only difference between them is a
restriction that would appear to have no actual effect on the event. But now con-
sider a simple two- situation case modeled on a reflection of Hunt’s (Fischer,
1999: 119–20). Imagine a universe correctly described by Epicurean physics
(Pereboom, 2001: 17). At the most fundamental level we find only atoms and the
frictionless void, and that these atoms fall in a determinate downward direc-
tion—except when they undergo uncaused swerves.
Situation C: A spherical atom is falling downward through space, with a
certain velocity and acceleration. Its actual causal history is indeterministic
because at any time the atom can be subject to an uncaused swerve. Suppose
that the atom can swerve in any direction other than upwards. In actual fact,
from t1 to t2 it does not swerve.A counterfactual situation diverges from C only by virtue of a device that elim-
inates alternative possibilities and all differences thereby entailed:
Situation D: This case is identical to C, except that the atom is falling down-
ward through a straight and vertically oriented tube whose interior surface is
made of frictionless material, and whose interior is precisely wide enough to
accommodate the atom. The atom would not have swerved during this time
interval, and the trajectory, velocity, and acceleration of the atom from t1 to
t2 are precisely what they are in C.One might initially have the intuition that the causal history of the atom from t1
to t2 in these two situations is exactly the same. However, this intuition might be
undermined by the fact that the restrictions present in D but not in C may change
this causal history from one that is essentially indeterministic to one that is
essentially deterministic. Because the tube prevents any alternative motion, it
might in fact rule out any indeterminism in the atom’s causal history between t1
and t2. And if the tube rules out any indeterminism in this causal history, it
would seem to make it deterministic.
This problem could make it hard to assess moral responsibility in blockage
cases. Sympathy for Frankfurt- style arguments is generated by the sense that
moral responsibility is largely a function of the features of the actual causal
history of an action, to which restrictions that are present yet play no actual
causal role are irrelevant. But in a scenario in which such restrictions may indeed
be relevant to the nature of the causal history of an action our intuitions about
whether the agent is morally responsible might be challenged. This concern may
make one less confident when evaluating these difficult kinds of Frankfurt- style
cases. Returning to Mele’s and Robb’s case, it’s a key feature of the example
that if Black’s deterministic process P and Bob’s indeterministic deliberative
process were to diverge at t2, P would neutralize N2 (which corresponds to not
deciding to steal the car) and all its cognate decision nodes. In this respect it