4.4 Modern Responses to Dualism

What this lecture covers

Having shown the problems with Cartesian substance dualism, this lecture surveys the modern alternatives: interactionism, epiphenomenalism, physicalism, and property dualism. Millican presents Frank Jackson's knowledge argument for property dualism, questions what "physical" even means given modern physics, and closes with the hard problem of consciousness.

You'll come away able to distinguish these positions, explain Jackson's Mary thought experiment, and state why the hard problem persists even once substance dualism is rejected.

Key ideas

• Interactionism: the common-sense view that mind and body causally influence each other.
• Epiphenomenalism: the view that the mind is a causally inert byproduct of bodily processes, with no effect on the body itself.
• Physicalism: the view that everything, including the mind, is ultimately physical.
• Property dualism: the view that there may be one substance but two distinct kinds of properties, physical and mental.
• Jackson's knowledge argument: Mary, a scientist who knows all the physical facts about color but has never seen it, seems to learn something new on first seeing color, suggesting that fact is non-physical.
• What counts as "physical" is unclear: modern physics deals in exotic properties like spin and charm, so the boundary of "physical" is far less obvious than it was in Descartes's time.
• Different kinds of explanation: a calculator's output can be explained mathematically as well as physically, illustrating that explaining behavior in intentional or purposive terms need not require a separate non-physical substance.
• The hard problem of consciousness: even once dualism's arguments are rejected, it remains puzzling why physical processes should be accompanied by felt experience at all.

Walkthrough

Positions after dualism (0:11)

Millican lays out the landscape of views available once Cartesian substance dualism is set aside: interactionism, epiphenomenalism, and physicalism, noting these terms recur frequently in the literature.

Jackson's knowledge argument (1:15)

He introduces property dualism via Frank Jackson's thought experiment: Mary knows every physical fact about color science but has never experienced color; when she finally sees color, she seems to learn something new, suggesting a non-physical fact about "what it's like" to see color, and hence a distinct kind of property rather than a distinct substance.

What is a "physical" property? (2:15)

Millican complicates the discussion by asking what "physical" even means once you move beyond the billiard-ball matter of early modern philosophy to a physics of exotic quantum properties. He raises, speculatively, whether consciousness could turn out to be physical in some future, unfamiliar sense.

Explanation and the hardware/software analogy (4:18)

Using the example of a calculator and a chess computer, Millican shows that explaining why a physical object behaves as it does can require non-physical (mathematical, or in the mind's case, intentional) terms without requiring a separate substance—much as software is distinct from hardware without being a different kind of stuff. He connects this to Gilbert Ryle's point that looking for "the mind" separately from bodily behavior may be a category mistake, like looking for "the university" apart from its colleges.

The hard problem (8:21)

The lecture ends by acknowledging that rejecting dualism's arguments does not dissolve the deeper puzzle: why should physical processes be accompanied by any felt experience at all? Millican presents this "hard problem" of consciousness as the residue of genuine puzzlement that outlives the failure of Cartesian dualism.

Before you watch

• Watch the previous lecture introducing Cartesian dualism and its problems, since this lecture picks up directly from the rejection of substance dualism.

Check your understanding

1. What is the difference between interactionism, epiphenomenalism, and physicalism?
2. What does Mary seem to learn on seeing color for the first time, and why does this challenge pure physicalism?
3. Why does Millican think it is harder than it used to be to say what counts as a "physical" property?
4. How does the calculator example show that non-physical explanations don't require a separate non-physical substance?
5. What is the hard problem of consciousness, and why does it survive the rejection of dualism?