William F. Vallicella's discussion on:
On Mind-Body Interaction, Conservation of Energy, and the Closure of the
A standard objection to interactionist substance dualism is that mind-body
interaction violates the principle of the conservation of energy. In my opinion,
anyone who finds this objection decisive is not thinking very hard. Let's
consider what C. J. Ducasse once said on the topic:
. . . The objection to interactionism that causation, in either direction, as
between psychical [mental] and physical events is precluded by the principle of
the conservation of energy (or of energy-matter) is invalid for several reasons.
A. One reason is that the conservation which that principle asserts is not
something known to be true without exception but is . . . only a
defining-postulate of the notion of a wholly closed physical world, so that the
question whether psycho-physical or physico-psychical causation ever occurs is
(but in different words) the question whether the physical world is wholly
closed. And that question is not answered by dignifying as a "principle" the
assumption that the physical world is wholly closed.
B. Anyway, as C. D. Broad has pointed out, it might be the case that whenever a
given amount of energy vanishes from, or emerges in, the physical world at one
place, then an equal amount of energy respectively emerges in, or vanishes from
that world at another place.
C. And thirdly, if "energy" is meant to designate something experimentally
measurable, then "energy" is defined in terms of causality, not causality in
terms of transfer of energy. That is, it is not known that all causation, or, in
particular, causation as between psychical and physical events, involves
transfer of energy. (Curt Ducasse, "In Defense of Dualism" in Sidney Hook, ed.,
Dimensions of Mind, Collier 1961, pp. 88-89)
I will now proceed seriatim through these points, supplying my own
interpretation of them.
Ad (A). Any physicalist worth his salt will uphold the causal closure of the
physical domain. That is just part (though not the whole) of what it means to be
a physicalist. Borrowing from Jaegwon Kim, the principle may be stated thusly:
Any physical event that has a cause at time t, has a physical cause at t. You QM
enthusiasts out there will please note that this does not imply that every
physical event has a cause. Note also that Kim's formulation seems to allow for
irreducibly mental events as causes of physical events. But if a physical event
e is a sufficient cause of a physical event f, then any mental cause m of f will
just be epiphenomenally along for the ride, if you catch my drift. In other
words, m won't do any work.
Adding to Kim's formulation the notion that physical causes are sufficient for
their physical effects yields a robust notion of causal closure. Robustly
understood, the causal closure of the physical domain amounts to the thesis that
all the causal work that gets done in the physical domain is done by physical
events; if there are any irreducibly mental events, they don't do any work in
the physical domain.
Ducasse's first argument, then, may be understood as follows. Appeal to
conservation of energy is equivalent to appeal to causal closure of the
physical. But one who objects to interactionist dualism on this basis begs the
question against it by assuming the truth of a principle (causal closure) that
immediately entails the falsity of interactionism.
The objection from conservation/closure is therefore not decisive against the
interactionist. It would be decisive if the closure principle were known to be
true. But that would be tantamount to knowing that physicalism is true. But we
don't know it to be true. Of course, physical science proceeds by searching for
physical causes. That is the kind of game it plays. Its procedure is
methodologically naturalistic. But there is a logical gap between methodological
and substantive naturalism.
Ad (B). I don't find Ducasse's second point all that impressive. Assume
conservation of energy. Then, if causation involves transfer of energy, and some
mental events are causally efficacious in the physical domain, then energy must
enter the physical domain at some point, call it the locus of interaction. Does
this violate conservation of energy? Only if it is assumed that energy does not
vanish at some other point. Since this is logically possible, the objection is
not decisive. In other words, there could be a net conservation of energy or
matter-energy in a system in which energy arose and vanished in different
Ad (C). Assume the causal closure of the physical domain. One could still be an
interactionist dualist by denying that mental-physical causation involves
transfer of a physical magnitude such as energy. Of course, if we know that
every instance of causation is an instance of energy transfer, then of course we
know (via some simple inferences) that mental-physical causation is impossible.
But we don't know this. Therefore, to object to interactionism on the ground
that all cauasation involves energy transfer is to beg the question against the
Note the difference between the first and third objections. The first objection
begs the question against the interactionist by assuming that it is known that
the physical domain is causally closed. The third objection begs the question by
assuming that it is known that causation always involves energy transfer.
It looks like we ought to distingish between the interactionist who accepts a
transfer theory of causation but rejects causal closure, and the interactionist
who accepts causal closure but rejects a transfer theory of causation.
Ducasse also alludes to the following point. Isn't transfer itself a causal
notion? How then can causation be analyzed in terms of transfer? Even if every
instance of causation were an instance of energy transfer, that would not entail
that causation consists in energy transfer. But this is a subtle point best
reserved for a separate post.