Hume’s Compatibilism

source Philosophy 322: Modern Philosophy Professor Geoff Pynn Northern Illinois University
Spring 2011

1 What is compatibilism?

1. Determinism

(a) Def. Condition C1 necessitates condition C2.
(b) divine determinism: Every event’s occurrence is necessitated by God’s decrees.
(c) causal determinism: Every event’s occurrence is necessitated by the occurrence of
the event’s cause together with the laws of nature.

i. Let L = the laws of nature and Dt = a complete description of all events in the
universe occurring at time t.
ii. Causal determinism (together with the assumption that every event has a cause)
is equivalent to the claim that ((Dt&L) leads inevitably to Dt+1)

(d) Note that divine determinism and causal determinism are logically independent.
(e) Note also that neither is equivalent to necessitarianism, the much stronger view that
all truths are necessary truths.

i. If God’s decrees are necessary, then divine determinism entails necessetarianism.
ii. If (a) there is some t such that Dt, and (b) L, then causal determinism entails necessitarianism.
iii. But most determinists would deny these assumptions.

(f) Hume is concerned with the compatibility of causal determinism and freedom. So
henceforth, casual determinism = determinism.

2. Freedom

(a) What is it to act freely? This is a contentious question. Best to start with examples of
(apparently) free acts:

i. This morning, I had Grape Nuts.
ii. I bought a lottery ticket last week.
iii. I went to Yale for graduate school.
1 means “necessarily”. ⊃ is the material conditional, which means roughly (though not precisely) “if… then…”

(b) The choices leading up to free acts can be constrained in various ways. E.g., I didn’t
have any Froot Loops, so I could have those for breakfast. Still, I freely had Grape
Nuts.
(c) The choices leading up to free acts can be (partly, though probably not entirely) in-
fluenced by outside or unconscious forces. E.g., even if I bought the lottery ticket in
part due to peer pressure, I still did it freely.

3. Incompatibilism: If determinism is true, then no agents are free.

(a) Intuitive argument. An act is free only if the agent could have done otherwise. But
if every act is necessitated prior to its occurrence, no agent could ever do otherwise
than she actually does. Hence if determinism is true, no agents are free.
(b) Incompabitilism seems to be the “default” position ordinary people take when first
exposed to these ideas. This was true of me and it is true of most students and nonphilosophers
I discuss it with.

4. Compatibilism: Incompatibilism is false.

(a) This is Hume’s view. He claims, surprisingly, that “all men have ever agreed […] and
that the whole controversy has hitherto turned merely upon words.”
(b) Hume’s defensive strategy (an example of a typical compatibilist defense; compare
what we saw in Leibniz): show that once we get clear about what we mean by “liberty”
(i.e., freedom) and “necessity” (i.e., determinism) we’ll see that they’re compatible.
(c) Hume’s offensive strategy: argue that freedom requires determinism; i.e., that if determinism
is false, then no acts are free.

Defensive move 1: free acts can be determined

1. Definition of “liberty”:

“By liberty, then, we can only mean a power of acting or not acting, according to the
determinations of the will; that is, if we choose to remain at rest, we may; if we
choose to move, we also may.” Hume

Cleaned up: S is at liberty with respect to A = (if S chooses to do A, then S will do A) & (if
S chooses not to do A, then S will not do A).

2. Consider a prisoner. He is not at liberty to leave his cell. On Hume’s definition, this means
roughly that it is not the case that (if the prisoner chooses to leave, then he will leave). The
guard, on the other hand, is at liberty to leave (or stay), since both conditionals are true of
him.

3. Hume thinks that this notion of “liberty” is the only one relevant to our idea of free action.

4. Here is a simple Humean account of free action. S did A freely if:
(a) S did A because S chose to do A;
(b) S was at liberty with respect to A.

5. This account makes free action compatible with determinism.
(a) I had Grape Nuts because I chose to.
(b) Just before I had Grape Nuts, it was true that (if I choose not to have Grape Nuts,
then I won’t have Grape Nuts), so I was at liberty with respect to having Grape Nuts.
(c) Neither implies that my having Grape Nuts was not causally determined.

Defensive move 2: “all mankind have always agreed…”

1. We all treat voluntary actions as caused by the agent’s motives; this is apparent from our
predictions and explanations of others’ behaviour. Indeed, it’s a requirement of the Hume inspired
account of a free act that it occur because it was chosen.
2. But what is it for one event (e.g., a choice or motive) to cause another (e.g., an action)?
Hume’s answer, in part, is that E1 caused E2 only if E1 necessitates E2:
“Let any one define a cause without comprehending as a part of the definition
a necessary connection with its effect […] and I will readily give up the whole
controversy.”
3. Thus, given that we regard voluntary actions as being caused by the agent’s motives, we
already regard voluntary actions as necessitated. (“[A]ll mankind have always agreed in the
doctrine of necessity.”)
4. Hume’s shrug: “You gotta problem? What problem? I don’t see a problem.”

Two problems with Hume’s defensive moves

1. Counterexamples

(a) Acts caused by addiction, hypnosis, brainwashing: all seem somehow unfree, but each
satisfies the Hume-inspired account perfectly.
(b) E.g.: as a result of expert brainwashing by my cult leader, I modify my will so that all
of my assets will go to him. I did it because I chose to, and it was true that (if I choose
not to do it, then I won’t do it). But, it seems, I didn’t freely do it.
(c) There are two ways to deal with these counterexamples (as always!):

i. First way: bite the bullet. Say that, despite appearances, such acts are fully free.

ii. Second way: modify the account. E.g., add another condition:
(c) S chose to do A because S had good reason to do A.
The brainwashing case seems not to satisfy this condition. I didn’t chose to modify
my will because I had good reason to; I did it because I’d been brainwashed!

iii. Other modifications are possible. Most contemporary versions of compatibilism
begin with something like the simple Humean theory sketched here, and build
from there.

2. Free actions vs. free choices

(a) Let’s suppose that Hume is right that we all regard voluntary actions as necessitated
by motives/choices.
(b) That doesn’t mean that we regard choices as necessitated by anything.
(c) Intuitively, we may want to add a third condition to the Hume-inspired account:
(c) S’s choice to do A was not necessitated.
Roughly: when I act freely, I could have chosen otherwise. More carefully: it was
possible for me to choose otherwise, even holding fixed all of my motives, reasons,
etc.
(d) But (c) is not compatible with determinism.

Hume on offense

1. Suppose we insist that free acts are, in some sense, not necessitated (perhaps because the
choices that cause them are not themselves necessitated). Then, Hume thinks, we are treating
free acts as chance events:
“[L]iberty, when opposed to necessity, not to constraint, is the same thing with
chance.”
2. Why? Remember that for Hume, causation implies necessary connection. If E1 didn’t
necessitate E2, then E1 didn’t cause E2. So the only way for E2 not to be necessitated is for
it not be caused by anything. An uncaused event is nothing more than a chance occurrence.
3. If causation doesn’t require necessitation, though, Hume’s offensive play won’t work: then
something can be caused, not necessitated, and not a chance event.

4. Still, Hume is onto something:
(a) Let C be the cause of act A. Suppose that A is free only if A is not necessitated by C.
(b) That means that it’s possible for C to occur without A.
(c) Consider the following two sequences of events: C → A and C → not A. What explains
why the first occurred, but not the second? Answer seems to be: nothing at all! It was
nothing more than luck or chance made the difference!
(d) But it is odd to say that A is free only if, by sheer luck or chance, C → A occurred
instead of C → not A. It seems to be the opposite result from what we’d want.

Appendix: Kant on Hume

Here is what Kant had to say about Hume’s compatibilism:
“This is a wretched subterfuge with which some persons still let themselves be put off, and so
think they have solved, with a petty word-jugglery, that difficult problem, at the solution of which
centuries have laboured in vain.” (Critique of Practical Reason)

Further