What is property dualism?

David Chalmers, answered from the texts and cited to the page.

David Chalmers answers

Property dualism is the view that conscious experience involves properties of an individual that are not entailed by that individual's physical properties, even though they may depend lawfully on those properties.¹ The route to this position runs through the failure of logical supervenience. If consciousness were logically supervenient on the physical, then any complete physical description of a world would entail everything about the conscious experience in that world — there would be no further facts to add.

But that entailment fails: a world physically identical to ours is conceivable without any experience whatsoever, which means that to ensure the facts about consciousness are as they are, something further had to be included in the world.² That further something is not a separate substance in the Cartesian sense. The physical world appears to be causally closed, leaving no room for a mental ghost in the machine to do extra causal work, so Cartesian interactionism is a stronger reaction than the arguments warrant.³

What the arguments do support is that phenomenal properties — the properties in virtue of which there is something it is like to be you — are ontologically independent of physical properties, even while they supervene naturally on them.⁴ The conditional I would press is this: if one takes consciousness seriously, accepting that there is something interesting to explain over and above the performance of various functions, then property dualism is the only reasonable option.⁵

Reject reductive functionalism and eliminativism, and it follows that consciousness is not logically supervenient on the physical; reject logical supervenience, and the path to property dualism is unswerving. The main remaining question is whether the fundamental properties in question are straightforwardly phenomenal or instead protophenomenal — but either way, something beyond the purely physical must be admitted as fundamental.⁶

Sources

1. The dualism implied here is instead a kind of property dualism: conscious experience involves properties of an individual that are not entailed by the physical properties of that individual, although they may depend lawfully on those properties.

   The Conscious Mind, pp. 104–105

2. To ensure that the facts about consciousness are as they are, further features had to be included in the world.

   The Conscious Mind, pp. 104–105

3. The best evidence of contemporary science tells us that the physical world is more or less causally closed: for every physical event, there is a physical sufficient cause. If so, there is no room for a mental 'ghost in the machine' to do any extra causal work.

   The Conscious Mind, pp. 104–105

4. All we know is that there are properties of individuals in this world—the phenomenal properties—that are ontologically independent of physical properties.

   The Conscious Mind, pp. 104–105

5. To take consciousness seriously is to accept just this: that there is something interesting that needs explaining, over and above the performance of various functions.

   The Conscious Mind, p. 138

6. Once we reject reductive functionalism and eliminativism, it follows inexorably that consciousness is not logically supervenient on the physical. And once we reject logical supervenience, the path to property dualism is unswerving... it follows either way that if we want to take consciousness seriously, we must admit phenomenal or protophenomenal properties as fundamental.

   The Conscious Mind, p. 138